Digital iconography, conflict heritage, and the teaching of history: The case of the Spanish Civil War

Abstract Computed-generated imagery (CGI) generates diverse views and perceptions of the past. These new experiences impact, directly or indirectly, the teaching and learning of history. This article presents didactic iconographic works on the Spanish Civil War created by the DIDPATRI (Didactics of Heritage and New Technologies) research group at the University of Barcelona. The didactic approach to this conflict reveals various problems that make it an interesting testing ground for new iconographies that contribute to an understanding of it. The proposal looks at the generation of “virtual” iconography to facilitate the teaching of content in formal and non-formal spaces. It is argued that CGI opens up possibilities to researchers, teachers, students, and technicians for the generation of comprehensive communication elements of history. The attractiveness of this new “virtual” iconography of the past lies in the possibility to create integrated ensembles where the facts, concepts, situations, and representations of materiality that the creators want to represent can appear. The resulting iconographic product can be applied for use in various environments, such as teaching, heritage, tourism, and cultural industries, and via different media, such as panels, apps, web, audio-visuals, museography, games, books, and notebooks.


PUBLIC INTEREST STATEMENT
The study examines the didactic possibilities of computer-generated images in the learning and understanding of historical processes. The interest in this new "virtual" iconography of the past lies in the possibility of creating integrated sets where the facts, concepts, situations or representations of the materiality that is to be represented appear. The authors, members of the DIDPATRI research group of the University of Barcelona, present the works carried out based on the specific episode of the Spanish Civil War. The didactic approach to this conflict adds very diverse problems that make it a good testing ground for testing new iconography that can contribute to its understanding.

Images, archaeology, and conflict heritage
The images generated to date of the past are examples of evidence that explain to us how humans represented, or how they imagined, their ancestors. From time immemorial, the events of the past have been transmitted through stories and myths. This "history" (understood as narration and memory) has been formalized as narrations, monuments, symbols, rituals, and images (Chartier, 1989(Chartier, , 1997. Iconography, a concrete and universal language, has always been used to explain the facts, concepts, and conceptual systems linked to history (Gow & Michalski, 2008;Parker, 2008). Its functionality is explained by the fact that an image is one of the best options for direct and understandable communication. The Stele of the Vultures, the bas-reliefs of Ramses III, the Trajan Column, the Bayeux Tapestry, the Panorama of Waterloo, and Hurley's photographs of Passchendaele are all formally realistic iconographic proposals, not abstract and, insofar as they are concrete, understandable.
On the other hand, thanks to technology, historical iconography provides both tangible and hypothetical insights into the past. The need to build personal and/or collective identities has caused an increasing demand for historiographical products. In this context, a virtuous triangle is defined between recreation as a means of generating images of the past, new digital iconography that enables 3D reconstructions and reorders the images generated by recreation, and a new tangible museography that bases its strategic socialization options on iconography (Sospedra-Roca, 2019).
The imagery of the Spanish Civil War is related to black and white photographs and films of the time. When the Spanish Civil War began, cameras such as the new Leica supplied images of war that had never been known before (Berthier & Sanchez-Biosca, 2012). Magnificent photographers such as Capa and Taro built an imposing iconographic repertoire that enables us to interpret the facts, landscapes, and ideas surrounding the conflict. These images constitute a powerful arsenal from a didactic point of view and can be exploited in the most diverse teaching-learning contexts (Feliu & Hernàndez-Cardona, 2013).
At present, images of the Spanish Civil War continue to be generated, while social interest coincides with initiatives such as the Historical Memory Law (Ley 52/2007(Ley 52/ , 2007, developed in Spain to promote democratic culture and to overcome the equivocal versions of the conflict developed by General Franco's regime. Interest in historical events, stories, characters, artifacts, heritage sites and structures demands a didactic iconography that facilitates their interpretation. To respond to the demand, subsidiary products of current technologies are generated, which create images with diverse purposes: instructive, educational, ideological, or playful. On the other hand, we must also bear in mind that societies imagine or represent the past from current perspectives, and with ideological or cultural filters (Pierrot, 2002;Raphael, 2012). The iconography of past conflicts may be accused of adopting current styles (Gombrich, 1983(Gombrich, , 1984Panofsky, 1979); however, from a strictly descriptive and didactic point of view, what is considered useful is the generation of realistic materials that facilitate, without distractions, an easy understanding of what is being communicated: what a trench was like, a section of an armored tank, the uniform of a soldier, the development of determined combat, etc. Artistic expression is one thing, but the explanation of an object of historical knowledge from a technical, trustworthy, and contextualized representation is another. In this sense, didactic iconography is a strictly technical matter, not necessarily a subsidiary of aesthetic options.
During the first decades of the 21st century, stories about history have undergone an escalation in realistic and immersive representation based on the advancement of these digital technologies. Digital iconography applied in gamification, audio-visual production, and museography has experienced spectacular development (Apel, 2012;Groot, 2016); however, the "represented stories" have not always been congruent with the knowledge generated by historical science. Nevertheless, historical and archaeological research has also made use of advanced iconographic resources; for example, GIS, photogrammetry, scanners, LiDAR, and georadar (Evans & Daly, 2006). However, the comprehensive iconographic communication of the knowledge obtained in historical and archaeological investigations has been limited to the generation of hypothetical recreations of virtual archaeology (Forte, 1997).
In recent decades, the market has responded to the demands of post-industrial society regarding the past, creating computer games, audio-visual products, and apps. Some of these products are of educational interest, and are even reused in classrooms and various heritage contexts (Haydn & Counsell, 2003;Jain et al., 2002). However, in general, teachers, heritage technicians, or tourist guides, can rarely relate these products with archaeological sites or with heritage elements, museums, or concepts studied in the classroom. These environments need accurate digital iconography products, in a content that is meaningful to their viewers. Similarly, historians and archaeologists who work in the context of public history and/or public archaeology (Cauvin, 2016;Merriman, 2004;Moshenska, 2017) need materials and applications that enable their research to be socialized. For these groups, the major product software on the market is not useful as it requires a very high level of professionalization and has an exorbitant acquisition and development cost.
The teaching and interpretation of the past need functional options for the generation of comprehensible images of the past that help influence school environments and broadspectrum users. We need iconographic products that are within reach that can be produced quickly and at a high quality and a low cost. The experiences and proposals that we present are intended to show that, using affordable software, quality didactic iconographies can be generated that facilitate an understanding of certain historical content. It is understood that didactic iconography of the past must be conceived as a virtuous triangle defined by: the technical domain of viable and affordable software at all times (in terms of cost and usability); the rules and doctrines that guide the creation of comprehensible images; and the demands of historians, archaeologists, teachers, heritage technicians, tourism, museography, students, and users in general.
In the case of the Spanish Civil War, as we have indicated, iconographic demands continue to generate diverse products: audio-visuals, gamification, documentaries, comics, graphic novels, museography, posters, didactic materials, interpretation centers, museums, recreations, and tourist routes. These environments use existing contemporary iconography of the events, but they also need and promote the creation of new images that can contribute to the understanding of events and places.

Hypothesis and objectives
We start from the hypothesis that realistic images of past conflicts can be generated from scientific information. However, digital technologies, in a continuous process of evolution, are optimizing the processes of representation, fostering a real revolution in the course of didactic understanding. In this context, the researcher must become the designer of these didactic images, since he is the one who must decide on the concepts and which real, movable, or anthropic elements are relevant. The resulting iconography is configured as an authentic didactic artifact, a model designed to facilitate the understanding of a certain fact, place, process, or concept (combat, military structure or infrastructure, attack system, uniformity, defensive line, aerial formation, etc.). On the other hand, it should be emphasized that the understanding of a place and its history requires congruence with the human contexts and movable artifacts that characterized it at the time, and that they must also be the object of representation.
To respond to these problems, the objective was to generate scientific and technological knowledge to enhance the understanding of conflictive pasts, especially of their historical and archaeological heritage, from the design of didactic iconography models. These models were based on 3D proposals, along with the superposition of anthropic elements obtained via the generation of 2D proposals and the application of techniques such as matte painting, or using animation or audiovisual options. The iconographic artifacts had to be able to be replicated with different supports and in varied environments (classroom, publications, games, museography, audio-visuals, virtual reality, augmented reality, and mobile telephony).
The research established a sequence that considered the difficulties of interpretation (learning) and a formulation of explanations (teaching) of historical issues. Once the cases were established, the aim was to optimize their clarity by creating new images. The initiatives were subjected to control, operation, and evaluation, and subsequently rectified. The research approximated the possibilities of iconic intermediation to increase the significance of the sources; that is, to establish what doctrine (strategies, practices, criteria, and techniques) the iconographic models could be designed on to represent the past in an understandable way.
The function of the intermediation of the iconography had to enhance the significance of the object of study for the observer/receiver, providing elements of linkage with the pre-concepts more generally accepted by a certain group of users (educational centers, non-formal teaching-learning, public in general). The objectives of the cross-sectional research were grouped into three large blocks. a) Objectives: teaching speech -Generate, experiment, and evaluate the different didactic criteria that should guide the design of historical iconography, establishing what should be shown and how: representations in diagrammatic blocks, points of view, colors, textures, representation of the human figure, representation of furniture, incorporation of information from parallel cases, and gender perspective.
-Establish the criteria that should govern the image-generation processes, taking into account that their function is to favor the interpretation of historical events and heritage spaces, and that the resulting criteria should apply to different types of portable and nonportable teaching materials, and didactic museum artifacts in situ.
-Define the characteristics of the different types of iconography and cartography suitable for interpreting heritage spaces and objects of knowledge based on different types of didactic mediation artifacts.
-Define the limits of the use of kinetic images based on the limits characterized by the object of study and the different types of supports.
-Analysis based on cases of extremely difficult historical and archaeological situations from the point of view of interpretation: ensembles with fragmentary structures, singular buildings, historical facts, and battlefields of the Spanish Civil War.

b) Objectives: iconography and technology
-Generate, experiment, and evaluate comprehensible didactic iconography from the images generated by georadar, gradiometer, scanning or photogrammetry in archaeological exploration and excavation processes (Tamba, 2016).
-Assess hypothetical 3D reconstructions as an instrument to formulate hypotheses about the forms, functions, and situations regarding patrimonial elements in the study phase.
-Analyze and evaluate the possibilities of creating historical re-enactment groups to generate digital images (photographic and kinetic).
-Analyze and generate audio-visual developments from the interaction of images generated from 3D, real scenarios (including recording with drones), and the activities of historical recreation groups.
-Analyze and evaluate iconographic developments using matte painting techniques in combination with images generated from 3D modeling and the iconographic treatment of real spaces. c) Objectives: knowledge socialization -Define models of didactic iconography based on emerging technologies that can be executed in minimal time and at a reasonable cost. Rehearse didactic proposals based on a broad range of contextualized heritage element iconography.
-Define models of didactic iconography that can be modified over time to incorporate new developments in scientific research.
-Influence the cultural industries related to teaching and heritage so that they can have quality iconographic elements that make it possible for students and users to understand.
-Define the characteristics and uses of the iconographic platforms in collaboration with the professionals involved in the management and use of heritage spaces (conservators, technicians, teachers, guides, businessmen, etc.).

Didactic iconography
The understanding and interpretation of the historical-archaeological heritage of contemporary conflicts are problematic (Carman, 2013;Schofield, 2005). This situation is accentuated in the case of the Spanish Civil War since, too often, the evidence is fragmented or decontextualized from the factual conjunctures, functions, and human activity that was present at the time (González Ruibal, 2016). The proposal that is formalized in this work maintains that the generation of ex-novo mediation images, which show the past from prototypes of didactic digital iconography that integrate knowledge and make explicit hypotheses, can promote a better understanding of the story.
Since 2010, the DIDPATRI research group has participated in historical-archaeological, heritage, museum, and educational research projects relating to the Spanish Civil War, which have required the generation of didactic iconography in order to generate materials aimed at educational centers, museums, and the media. In this context, a reflection on didactic iconography has also become a cross-sectional meta-project, while common methodological denominators have been sought to address recurring problems in the various cases involved.
The methods used in each case had their own characteristics, but all the projects were planned based on a common research denominator: to establish intervention hypotheses, develop them, and subsequently experiment with them. The investigation was also planned to be triangulated; that is, the agents involved had to establish perspectives of analysis and assessment. The methodology was similar to the "experiment or quasi-experiment" method. Prototyping projects are usually located in the socio-critical paradigm, with the incorporation of qualitative-comprehensive components. Apart from the socio-critical framework, the lines of research had an empirical character, being based on proposals that could verify and contrast compressibility. In other words, it was possible to estimate whether a certain iconographic proposal contributed to facilitating interest, understanding and/or the acquisition of knowledge, and to quantify the results obtained.

Cases worked
Between 2005 and 2020, the DIDPATRI research group conducted various historical-archaeological investigations regarding the Spanish Civil War that involved the development of a cross-sectional meta-project of didactic iconography to socialize the knowledge generated and apply it to formal and non-formal education. The main projects were as follows.
Between 2005 and 2010, research campaigns were carried out on the Republican airfields involved in the Battle of the Ebro and the Catalonia Campaign (1938)(1939). Geophysical prospecting was used and an extensive historical-archaeological investigation was developed. The practice of socialization took shape from the creation of a Republican Aviation Interpretation Center (CIARGA) in the municipality of els Monjos (Tarragona) (Arnabat & Hernàndez et al., 2011;Hernández-Cardona, Íñiguez-Grácia;Gesalí, Rubio-Campillo, 2020). A digital iconographic program was made from matte painting illustrations and an adaptation of computer games. At the same time, at the la Garriga aerodrome (Barcelona), open-air interpretation didactic stations were tested, aimed primarily at school groups (Coma & Rojo, 2010;. Starting in 2011, various archaeological projects were conducted around the La Fatarella conflict (November 1938), the last great confrontation in the Battle of the Ebro (Gonzalez Ruibal, 2012;González Ruibal, 2016). Sections of the Riba-Roja/Fatarella/Ascó fortified line were excavated and an iconographic program for a 3D reconstruction of the fortified line was developed . Various audio-visual proposals were also made, in which the collaboration of reenactment groups was tested to obtain images with anthropic elements. The socialization endeavors also involved museum activity and the production of teaching materials.
In 2016, we carried out an archaeological excavation of the command post of the British Battalion of the XV International Brigade during the Battle of the Ebro (1938) in the Molí d'en Ferriol, Corbera d'Ebre (Tarragona). An iconographic program based on matte painting was developed, and the photogrammetric recreation of the site and the preparation of didactic materials were accomplished (Romero, 2018).
In the years 2018 to 2020, a project was undertaken that focused on the physical reconstruction of a pillbox on the beach of Cunit (Tarragona), a heritage element built in 1938 to defend the coast that had been destroyed in the 1970s. The museum proposal had an iconographic program with scenographic and audio-visual elements (Sospedra-Roca & Hernàndez-Cardona, 2018).
In 2018, an archaeological excavation of the Vall de l'Obaga (Corbera d'Ebre, Tarragona) was carried out. The remains of Robert Merriman, commander of the Lincoln-Washington Battalion of the XV International Brigade, were especially sought. The remains of Major Merriman were not located, but an audio-visual proposal was made to explain the research and the activities of the international volunteers of the XV Brigade (F-X . Between 2019 and 2021, the Hospital del Molar Interpretation Center was designed and executed, an ambitious museum proposal for the creation of a Republican army field hospital from the Battle of the Ebro (September 1938). The realization of the museography implied an ambitious scenographic, iconographic, and audio-visual program that was carried out with the collaboration of historical recreation groups .
In the years 2020-2021, the Santa Coloma de Gramenet (Barcelona) anti-aircraft shelter museumization project was carried out. The proposal involved the possibility of making an audio-visual program adapted to the difficult conditions of the construction galleries (Sospedra-Roca & Hernàndez-Cardona, 2020).

A doctrine of didactic iconography
The results of the empirical studies carried out in the Spanish Civil War case environment allowed us to make explicit a "doctrine", or, if you will, a methodological systematization, for the generation of sustainable and comprehensive digital iconography of the history and archaeology of the conflict, which can be extrapolated to other objects of knowledge and heritage elements of the past. It should be understood that the definition of a "doctrine" implies a common and systematic way of dealing with similar problems regarding transference. The doctrine allowed the application of strategies and tactics that, as they were implemented, helped to correct, clarify, and advance the doctrine itself.
The doctrine was understood as a set of variables of a cultural, technical, or functional nature that, acting simultaneously, generated a stable situation in terms of the selection of options. The ideas, resources, strategies, and technologies included in the doctrinal package fed back to each other, which is why they formed an effective and identifiable block, and why, globally, they defined systematic action guidelines to consider or face in the resolution of an intervention.
The initial variable of the doctrine establishes that economic availability (the budget) is important, but not decisive. A big budget does not guarantee anything, but a limited budget can be unfeasible. Creativity, the existence of clear objectives, and tactical experience always help to optimize results. Ideally, the public-history and public-archaeology teams, or their direct environments, assume the iconographic production duties, or they incorporate technicians capable of doing so, and they interact from the first moment. However, in many cases, the collaboration of qualified professionals will be necessary to optimize the proposals. In any case, researchers must also have a transfer "project", and criteria to choose what type of didactic iconography they are interested in developing. The proposals will be sustainable as long as they involve reasonable costs, but they also depend on the results, and the fact that the efforts affect the creation of a quality citizenry, the conservation of heritage, and its orientation as a source of wealth creation.
Technology and technique are also part of the structure of an iconographic doctrine. Between technology and technique, there will always be tension. Technology is constantly evolving, implying the incorporation of new software and hardware proposals. In contrast, the dimension of technique, which focuses on guidelines for action and criteria, is not necessarily a subsidiary of technology. The dynamics are raised inversely, technologies are coupled or considered insofar as they can be integrated into techniques, understood as tactics, or guidelines of action assumed by the producer group. The team that has more and better technological resources will be at an advantage, provided that it can use them with trained personnel and in a manner consistent with the innovations that are intended to be carried out. Having technological resources does not necessarily imply that you are capable of innovating or managing more effectively.
The doctrine must always consider the "experience of the path"; that is, to optimize from previous experience without attempting risky or uncertain practices. The adaptability of a team to cope with unforeseen situations or changes should also be advocated. Flexibility is very important, and so is the decision-making capacity of its components. The doctrine, with regard to the iconography of conflict, culminated in being systematized through the use of 3D to recreate places, incorporating anthropic elements with images obtained from historical re-enactments, and using matte painting or video techniques to assemble proposals

The importance of 3D
In the iconographic reconstruction of a conflict space, a 3D survey that allows navigation and the selection of different points of view, along with a global and comprehensive perception of the represented space is always advised. The oblique aerial view is always the clearest, but 3D also allows for the generation of 2D and animated still images indistinctly that can be used on different media (Hermon & Kalisperis, 2011). These 3D surveys are useful for representing structures and infrastructures, as well as battlefields. They can also be used to approximate artifacts (weapons, vehicles, ships, airplanes; Macdonald, 1986Macdonald, , 2015. In the different interventions developed by the DIDPATRI group, 3D surveys were carried out in spaces as diverse as the command post of the British Battalion of the XV International Brigade in Molí d'en Ferriol (Romero, 2018); the fortified line of la Fatarella ; and a pillbox on the coast of Cunit. The most notable experience was the 3D reconstruction of the fortified line of Fatarella Ridge (a space of approximately 12 hectares), a defensive complex typical of the first half of the 20th century constructed with trenches and concrete forts. It featured entrenched fields, anti-tank ditches, and a total of eight pillboxes. In November 1938, the area was attacked by General Franco's fascist troops and a bloody battle was fought (Rubio-Campillo & Hernàndez, 2015). During the post-war period, the forts were blown up and the trenches disappeared due to agricultural activities. Starting in 2010, the space was meticulously studied (Rams, Pérez, 2010), and some sections were excavated and recovered. The information extracted from the successive archaeological campaigns, the work with documentary sources, and the in-situ recognition of visible remains allowed for a reasonably reliable virtual reconstruction proposal.
The objective of the 3D reconstruction was to create multipurpose digital material to explain the battlefield in panels, audio-visuals, publications, didactic materials, apps, guided tours, virtual and augmented reality, etc., which also needed be useful as a basis for 2D iconographic proposals that incorporated movable and anthropic elements. It is understood that 3D is a type of artifice that can be assembled or re-adapted for the most diverse didactic functions and supports, and it is in this aspect that its usefulness lies.
For surveys of this type of space, it is recommended that free software programs such as Blender are used, as they are relatively simple to use and have integrating texture possibilities. Programs such as 3D Studio Max also offer good prospects; while programs such as Unreal or World Creator (for landscapes and terrain) require time and professionalism. The experience, and the consultations with technicians and users, revealed an interest in the use of a realistic or hyper-realistic aesthetic and color, ruling out monochrome or other simplified options in terms of layout. Some 3D reconstructions, especially those made by architects and designers in museum settings, tend to use greyscales and simplification options. However, if the objective is didactic, and focuses on making a space understandable, it must be represented with all its characteristics in terms of frames, shapes, and colors, and even, if possible, incorporating movable and anthropic elements. We can summarize the doctrine followed by indicating that it involved using software that was not excessively complex, and that the spaces were represented based on realistic or hyper-realistic criteria (Figures 1-4).

The problem of human representation
In iconography, human representation is always a complex issue. In conflict situations, often involving extreme positions and expressions, along with complex equipment, the problem increases. If you start from the base of space built in 3D, you can consider the integration of humans modeled also in 3D. However, modeling human volumes in 3D requires experience and professionalism. On one hand, the results obtained with the most affordable programs generate figures that can be somewhat rigid and unnatural. On the other hand, the need for truthfulness implies continuous modeling for different individuals to show anthropometric and team diversity. During the Spanish Civil War, a significant variety of helmets, uniforms, and weapons were used, and a realistic option would require us to respect this diversity, which is not easy using 3D modeling. Nevertheless, programs such as Blender allow you to model human figures. Daz Studio 3D or Metahumans require more complexity and technical proficiency. On the other hand, the incorporation, in 3D, of animated humans or the use of game engines, such as Unreal for video games or movies, demands a very high degree of specialization.  However, the option of modeling humans in 3D is not the only possible solution in static iconography. The use of matte painting techniques to obtain credible images is also a very good solution. It generally consists of constructing complex collages, using a photograph as a base that is superimposed on photographic backgrounds or generated in 2D from a reconstruction in 3D. The various iconographic projects developed by DIDPATRI were constructed by using the matte painting technique, using photographs of humans combined with photos of real or reconstructed spaces in 2D or 3D. The iconographic doctrine of DIDPATRI used in the different projects specified the use human figures generated from historical recreation and adapted from matte painting techniques using affordable software (Jiménez Torregrosa & Rojo, 2014). The images were created from the GIMP free software program, but Photoshop-type programs, Paint.NET-type photo editors, Photoscape, etc., could also be used (F. X. Hernàndez-Cardona et al., 2019;Figures 5, 6).

Support in historical recreation
Historical re-enactment is an emerging social practice in various social and educational settings (Agnew et al., 2019;Dupré et al., 2020;Goodacre & Y Baldwin, 2002). Normally the re-enactors have extensive knowledge of the period being represented, implying that their teams will be accurate and congruent with the period represented. The re-enactor is always an interesting simulator as a generator of credible images of the past. The strategy developed by DIDPATRI consisted of extensively using static or kinetic images obtained from historical re-enactment in the elaboration of iconography.
DIDPATRI has developed, in parallel to its research, the promotion of historical recreation. The group has maintained good relations with the existing Spanish Civil War re-enactors and, together with some of them, has organized recreation events to enhance the sites on which it has studied. Thus, the "UB Recreation-DIDPATRI" recreation group, dedicated primarily to the Spanish Civil War and linked to the University of Barcelona, has been created . With the collaboration of the re-enactment groups, a large bank of images has been built that can be used in various cases and functions. In addition, the collaboration facilitated the acquisition of ad hoc images based on didactic needs, making it possible to recreate a certain trench, certain combat, daily life in a shelter, a surgical operation, a field hospital, a rearguard school, or an office, with the re-enactors maintaining attitudes or poses congruent with the iconographic proposal to be developed. This constitutes a true didactic revolution insofar as it is possible to accurately create iconography and represent anthropic and movable factors in any type of space. Naturally, the images of re-enactors can also be placed on 2D backgrounds generated from 3D.
The images obtained can be used directly or treated with a matte painting technique and integrated into any type of background that is considered accurate. As indicated, the use of recreation has not only facilitated the production of diverse fixed iconography, but it has also contributed to the realization of audio-visual proposals.
Faced with this use of recreation, it could be argued that the images are not real and that the use of recreation could generate misunderstandings or fakes. However, it should be borne in mind that the use of computer-modeled images does not imply reality either, and that the use of fake effects could be prevented with a simple warning or by formalizing the entire illustration generated (Figure 7).

Use of matte painting
The development of historical-archaeological and patrimonial iconography proposed by DIDPATRI has always been defined by the generation of precise images to obtain a reliable representation of an event or a place from the past. To satisfy this need, the use of matte painting was chosen, an iconographic creation technique that originated at the beginning of the 20th century with the use of painted glass to engrave certain cinematographic scenes. These days, matte painting uses image-processing software to create scenarios or to recreate eras (Mattingly, 2011). As indicated previously, the software used by DIDPATRI was mainly GIMP-type programs or Adobe Photoshop, without losing sight of the possibilities that Unreal or World Creator could offer at certain times.
Matte painting requires defining a background on which to superimpose movable elements and anthropic actions. The background can be obtained from photographs or retouched images of the present, eliminating or adding the most diverse aspects; however, it can also be generated, directly, from 3D, if such process has been carried out. From a certain landscape or place raised in 3D, a specific point of view can be chosen to generate a 2D image on which anthropic elements or furniture with different types of finish can be superimposed (Íñiguez et al., 2017). DIDPATRI tested different proposals. One consisted of generating all the intervention images in black and white; certainly, the option was congruent with the iconographic image of the Spanish Civil War. However, this option, which could work in some museographic or scenographic spaces, was not extrapolated at the doctrinal level, as the lack of color implies a deficit of information. Another option consisted of the elaboration of a photographic collage in color. Finally, a third option was based on the use of collage in color, but giving an aesthetic rectification to the images to give them the unequivocal appearance of an illustration; that is, turning the photograph into an illustration. Examples of all three options can be found in the numerous iconographic interventions carried out by the research group. Illustrations in black and white were used in the graphic and audio-visual production of the el Molar interpretation center (Priorat, Catalunya). Proposals of  a more photographic nature, in color, were used in the design of various didactic and museum materials, such as in the realization of the graphics for the pillbox in Cunit (Baix Penedès, Catalunya), and color illustrations were predominant in the majority of the created proposals and publications (Figures 8, 9).

Use of audio-visual elements
A cinematographic option has always accompanied DIDPATRI's research, innovation, and transfer interventions in the Spanish Civil War environment. Audio-visual initiatives have often been used to explain certain studies, to chronicle an event, or as a museum asset (Burgoyne, 2009). The generation of audio-visuals included diverse resources: live recordings at the sites, interviews with scientists, and interviews with witnesses; however, it also included approaches to the time, which in some cases were covered from contemporary documentaries (if the images were congruent) or from new recordings using re-enactors. As in the case of fixed iconography, in audiovisual production, we requested collaboration with historical re-enactment groups. The most diverse scenes were made in real or plausible settings, and in some cases, with the use of the green screen technique, to place backgrounds congruent with the spaces that were to be shown during post-production. The audio-visual results are more than correct, highlighting "epic" productions, such as the audio-visual produced on Republican health during the Spanish Civil War, which included the recreation of surgical intervention in a field hospital , or the documentary on the archaeological intervention that sought to recover the remains of the commander of the International Militias, Robert Merriman (Figures 10, 11).

Discussion
DIDPATRI interventions in the Spanish Civil War environment have always been considered from the perspective of public history/public archaeology, taking into consideration, on one hand, the formal teaching/learning spaces, but also the non-formal ones (Demantowsky, 2018;Thomas & Lea, 2014). This has implied a consideration of the socialization of knowledge and working so that the content could influence the formation of a quality citizenry and the generation of wealth. Taking into account that the historical past is not directly visible (it is only perceptible from its evidence), the didactic program regarding the objects of the study had to take into account the generation of comprehensible images that could act as mediators. This entailed the definition and experimentation of an iconographic program. However, this proposal is automatically mediated by the iconographic culture that, with regard to history, has generated gamification and some quality film productions (Elsaesser, 2019;Slator, 2006). These are excellent products with which students and the general public coexist daily, and which, for a wide sector of the public, are considered "normal" standards. Nevertheless, these productions, not linked to the local or near reality, need large investments. The didactic iconography that museums or educational centers with limited budgets can produce cannot compete with these large productions (Parry, 2013).
In this sense, we must consider that the generation of iconographic elements in history depends, in part, on the resources allocated to their production. However, resources are not decisive, as already noted, and the challenge is to make the right products from tight budgets. Furthermore, in this discussion, it seems necessary to isolate the technological variable since the quality of the product will always be a function of the available software; although this is a variable that changes depending on the evolution of the software itself. Productions that today are unthinkable due to their high technological and professional cost may shortly be feasible. We start, however, from the basis (supported by empirical experience) that resources are always limited, and in this sense, the sustainability horizon of a proposal should point to the fact that the use of affordable software does not imply a high degree of professionalization.
The practice of experiences in the context of public history and public archaeology indicates the benefit of the composition of large, multipurpose, interdisciplinary research teams. Archaeologists and historians must be flanked by professors, teachers, didacts, local scholars, museographers, cartographers, and illustrators; while in a second ring, other actors must also be considered, such as journalists, tourism operators, heritage and audio-visual technicians, and political or governance officials. We understand that the image plays a fundamental role and, in this sense, experience allows us to claim the importance of including technicians or researchers with the ability to work in digital cartography, 3D surveys, and various iconic representations in research (Limp et al., 2011).
On the other hand, the suitability of historical re-enactment initiatives must be considered. The alliance with historical recreation environments allows for the dissemination tension to be sustained while the investigations last, and even afterwards in the maintenance and promotion of the patrimonial artifact. However, re-enactment is also extremely useful in generating didactic iconography that can be used before, during, or after an investigation, and from the most diverse supports. DIDPATRI's experience in the Spanish Civil War environment means that we explicitly value collaboration with re-enactors, and even advocate interest in participating or directly creating recreation groups that can support research and knowledge socialization tasks (Hernàndez & Romero, 2014).
Finally, it should be noted that the main axes regarding the creation of didactic iconography: the use of software that is not excessively complex; the use of 3D surveys; the use of matte painting techniques from GIM-type software; the use of furniture and anthropic elements; and the systematic use of re-enactment present relevant possibilities for the use of informal teaching-learning spaces. Students can participate in historical re-enactment actions, even from a servicelearning perspective, obtaining images from sites or 3D images already executed, and creating  their compositions using matte painting. In other words, the strategies and techniques are used to facilitate direct didactic action that offers students comprehensible images of the past, but it can also facilitate more proactive didactic strategies that are more synchronous and congruent with the scientific method of discovery (Haydn & Counsell, 2003). If a student proposes to create an illustration in which a certain historical event, a process, or daily activity is reflected, this will logically imply an interesting inductive process, making the student the protagonist of their research (Figures 12, 13).

Conclusions
The Spanish Civil War, a conflict that occurred in the first half of the 20th century, has relevant iconographic sources. However, the demand for the iconography of this conflict continues to explain and create an understanding of the concepts, unique stories, heritage elements, museum spaces, and even tourist circuits.
In the various research and transfer projects carried out by the DIDPATRI group (in the contexts of public archaeology and public history), a comprehensive iconography has been generated that helps to socialize historical, archaeological, and patrimonial issues, and which affects society and educational environments. This production of images, contemporary to the investigation and conceived as proximity iconography, can pivot to representing historical or heritage spaces using 3D images and matte painting. Regarding the treatment and incorporation of the human figure in the iconography, without ruling out the use of programs with the ability to model, the magnificent results that derived from the use of images obtained from re-enactment groups stand out. At the same time, re-enactment also implies great possibilities in terms of kinetic images, since the actions carried out on various backgrounds, including 3D, allow the most diverse situations to be reproduced or evoked. The possibility of incorporating re-enactment groups in the context of carrying out, transferring, or disseminating certain research is emerging as a compelling strategy from an iconographic point of view.
From the experiences gained in the presentation of a contemporary conflict, a praxis has emerged that proposes the use of software that is not excessively complex, along with an interaction between technologies and techniques that allows for the generation of quality products that can be stored, redesigned, and reapplied in successive productions, and which also implies a factor of economic sustainability. The iconography of proximity produces greater possibilities for understanding, and this affects the formation of an informed citizenry aware of their past.