Innovative solution for relief printing without limiting heights

Since 2014, IGN has been monitoring advancements in technology to explore a colour relief printing service for on-demand mapping

François Lecordix National Institute of Geographic and Forest Information, France

Abstract

By following advancements in 3D printing technology, IGN explored an inkjet-based relief printing solution proposed by the Océ company in 2015. The initial results were presented at the International Cartographic Conference in Rio de Janeiro, showcasing the Belle-Ile map. This technology addressed several critical needs for relief mapping, including high printing resolution, large size, and accurate colour reproduction. However, it still faced two significant issues: high production costs for the general public (compared to thermoformed maps produced in multiple copies) and limited printing heights (less than 2-3 cm). In 2022, IGN introduced an innovative solution to address the limitation of printing heights without increasing production costs. This new approach combines the previous inkjet relief printing technology with Stratoconception® technology from the 3D printing domain. The details of this solution, along with an example result, are presented in this paper.

1. Introduction

During the Second World War, the demand for relief maps surged on both sides of the conflict, leading to the development of new production methods. For example, the American ribbon method (Sutter et al., 2006) accelerated the creation of initial moulds, while the German Wenschow method (Reed, 1946) also contributed to faster production. After the war, the Americans, inspired by Wenschow’s approach, adopted thermoplastic sheeting to develop the thermoforming process, which still remains the solution for producing relief maps worldwide.

In France, for instance, the National Institute of Geographic and Forest Information (IGN France) continues to produce relief maps using the thermoforming process. They print on vinyl sheets and use specially created moulds, provided that the mapped area generates enough demand to justify the costs of producing the various intermediate models. The minimum threshold for producing a first edition of relief maps is approximately one thousand copies.

However, there is a growing need for ondemand relief mapping across the country. This demand is also evident on a global level, as demonstrated by the TouchTerrain web service, which recorded 38 requests per day for print-ready digital terrain models between July 2019 and January 2021 (Harding, 2021). Despite this, the 3D prints produced by TouchTerrain are monochrome. Users must either handcolour their 3D prints or supplement them with 2D colour maps to effectively combine the relief and paper mapping.

While there is a clear need for on-demand 3D printing, existing solutions either fall short for large formats or, for smaller formats, suffer from mediocre quality or excessive cost. These limitations prevent the current solutions from effectively addressing the demand.

Since 2014, IGN has been monitoring advancements in technology to explore a colour relief printing service for ondemand mapping, aiming to avoid the high costs associated with the thermoforming for only one exemplary. A notable French technological innovation was introduced at the ICC 2015 in Rio de Janeiro, which enabled the production of colour relief maps, though it had height limitations. Building on this technology, IGN presents an innovative solution in this paper that addresses the height limitation and includes the first experimental results.

2. Existing Solutions for Relief Mapping

2.1 Thermoforming

Developed in 1947 by the Army Cartographic Service in Washington (Stanley, 1947), thermoforming relief mapping involves the creation of three intermediate models:
• A master model in plaster (originally aluminum), which represents the relief derived from geographical data. This model can be adjusted to refine certain areas. It cannot be used directly for thermoforming due to its insufficient strength. Nowadays, these models are typically produced using 3D printers from digital terrain models (DTMs).
• A negative of the master model, which creates the relief in hollow form.
• The final mould, created from the negative by casting a durable resin (such as epoxy), which reproduces the initial model. This mould is then perforated at multiple points to create air suction wells, allowing printed maps to be affixed to the matrix through suction.

Once the mould is produced, the production of relief maps by thermoforming can begin. For this process, the map is printed on vinyl sheets, either in large quantities using offset printing or in smaller quantities using a digital press. After the ink dries, the vinyl sheet is carefully aligned with the mould. Air is then removed from the vacuum chamber using a vacuum pump. The vacuum pulls the vinyl sheet tightly against the mould. Heat is applied to the vinyl, softening it so that it conforms to the mould under considerable force. The embossed vinyl map is then allowed to cool in the mould while maintaining the vacuum pressure.

Due to mechanical constraints, not all relief forms can be achieved with thermoforming. For instance, large slope breaks are impractical because they would damage the vinyl sheet. These technical limitations require that the relief shapes be smoothed out on the initial mould in advance, and certain shapes may need to be excluded.

It should be noted that this process is linked to the 2D printing world. The process begins with a 2D print that is then transformed into a representation often referred to as 2.5D (a 2D surface deformed into a 3D) rather than 3D.

2.2 Additive manufacturing from the world of industry

Additive manufacturing has advanced rapidly in recent decades, with several technologies emerging to meet various needs, some of which are now accessible to individuals. Once a 3D digital model is created and adapted to the chosen printing solution, several production technologies come into play, as detailed by Barlier (2020):
• Polymerisation of a resin under the action of a laser: A resin bath is solidified layer by layer under the effect of a catalysing agent (e.g., UV laser, red actinic bulb, etc.).
• Spraying of drops of material (lightcuring resin, molten wax, etc.).
• Projection of a binder onto a powderlike substrate. This family includes all processes that apply the basic process known as 3D printing. They allow printing with different colours.
• Solidification of powder under the action of a medium to high power energy source (laser or electron beam).
• Projection of powder (or wire fusion) in an energy flow (laser or plasma). Here, all the processes that produce 3D objects by depositing molten material are grouped together. They allow the fusion of many metallic materials such as stainless steels, titanium alloys, from several variants of the deposition nozzle, the main component.
• Melting of wire through a heated nozzle. This process, the most widespread for the general public, consists of depositing molten wire through a nozzle to print in successive transverse 3D layers. This technology allows the use of thermoplastic materials, wax, but also more original materials such as chocolate.
• The assembly of layers from cut sheets or plates. This category covers processes based on materials available in sheets. These sheets can be continuous, e.g. in the form of rolls, but also discontinuous, e.g. in the form of plates of different materials, from wood to steel (Stratoconception). These additive techniques involve cutting and joining or joining and cutting of these sheets.

Hybrid additive manufacturing consists of combining at least two of its processes. The objective of these combinations is to take advantage of the different performances of the processes as well as their complementarity.

2.3 Limitations of existing additive manufacturing for relief mapping

The additive manufacturing solutions listed above are insufficient for meeting the needs of relief cartography. They fall short in several areas: insufficient size (a minimum size of 1 m2 is desirable to ensure the production of maps for the IGN catalogue), printing resolution too low in powder-based solutions to consider printing writing (400 dpi minimum), low colour diversity, insufficient robustness and quality for solutions that use coloured sheet assembly, etc.

2.4 The first significant step towards printing relief maps

In 2015, at the ICC in Rio de Janeiro, IGN presented the first large size relief map obtained by 3D printing with the ACI award-winning map of Belle Ile. This relief or 2.5D printing technology, proposed by Océ, a subsidiary of the Canon group, utilized an inkjet printing solution with the capability of adding thickness to the ink to create relief. Although Océ abandoned this printing solution in 2016, it was revived in 2020 by the startup Mihaly, founded by the French designers of the original technology who had previously worked for Océ.

This technical solution was detailed at the Time, Art & Cartography conference, held during March 16-18, 2016 at the University of Strasbourg, France. During the conference, Lecordix presented a large-format (105 cm by 135 cm) relief map of the Battle of Verdun (2016). The conference also provided an opportunity to experiment with a graphic semiology adapted for relief representation, following the manufacturing process illustrated in Figure 1.

A digital surface model is created by combining the relief data from the Digital Terrain Model (DTM) with the elevation heights assigned to various map features (such as paths, houses, and tourist points) according to choices of the relief legend. This model is then used in conjunction with a coloured raster map of the same area. The printer utilizes both files to precisely build up the relief by depositing grey ink in layers that correspond to the elevation data. At the end, CMYK inks are applied to colour the top of the relief, resulting in a colourful relief map.

The proposed technology addresses several key needs for relief mapping, including high printing resolution (600 dpi), large dimensions, and accurate colour reproduction. However, it faces two main challenges: the relatively high printing costs for the general public (compared to the lower prices of thermoformed maps produced in multiple copies) and, more importantly, the still limited printing heights (less than 2 to 3 cm).

3. Cartographic stratoconception

3.1 Thermoforming

In 2022, IGN proposed an innovative solution to address the issue of limited printing heights without increasing production costs.

This solution was inspired by the cardboard dog head exhibited by CIRTES company at trade fairs (Figure 2) and was realised by the patented Pack&Strat® application. This application is dedicated to 3D digital rapid packaging and uses the patented Stratoconception® rapid micro-milling process which works for materials such as wood, carboard, foams, etc. In this process, cardboard and foam are cut using a computerguided cutter. The dog head, which evokes the concept of contour lines, demonstrates the possibility of creating shapes without height limitations, serving as the inspiration for the innovation described below. The process is based on a hybridisation of the previous inkjet relief printing technology existing in the world of digital plotters with the Stratoconception® technology existing in the world of 3D printing, which will be detailed below.

3.2 Stratoconception® developed by CIRTES

The description of the Stratoconception® technology is described by its designer Pr. Barlier (2020) (Figure 3):

The Stratoconception® process was initiated and patented by Claude Barlier in the mid-1980s and was commercialised in 1991. This is a solid layer additive manufacturing process which consists of breaking down the CAD model of the part by calculation into a set of elementary 3D layers, called “strata”, into which reinforcements and inserts are introduced. The elementary layers are put in a panoply (front/back) and manufactured in a plate material by means of rapid micro-milling, laser, water jet or cutter cutting. These thick 3D layers represent a slice very close to the original CAD model – unlike other processes which reconstruct the part from single 2D layers – they are produced directly in three dimensions by 5-axis cutting, which makes it possible to obtain ruled surfaces, or better still by 2.5-axis rapid micro-milling. In the latter case, the profile is representative of the initial 3D CAD, in terms of size, geometry and surface finish. Figure 1. Process to prepare the two raster files for relief printing of Belle Île The layers are then positioned with inserts, or interlocked or joined with bridges to form thin-walled parts to create the final object. The final assembly can be achieved by mechanical joining, structural bonding, brazing, diffusion welding or hot isostatic pressing (HIP) depending on the material and the intended end applications. In some cases, it is possible to finish the layers after assembly by stacking (integrated into the process). The means of positioning and the type of assembly are taken into account from the moment the object is broken down, and contribute to the mechanical strength of the parts.

This solution provides a basis for creating a relief without height limitation using a strata support, to which the colour and final shape of the relief must be added.

3.3 Cartographic Stratoconception

As previously mentioned, the inkjet technology proposed by Mihaly involves applying specific ink onto a layer of support. By accumulating progressively with each scan of the surface, this ink will rise progressively to obtain the desired relief and the final layer will be carried out by inkjet in CMYK on this relief. The proposed elevation is limited to a height of 2 to 3 cm. A schematic cross-section of the printing process is provided in Figure 4.

In the proposed innovation for relief printing, the elevation file is duplicated in two files, called even and odd layers, which will undergo similar but offset processing to bring the height of the raised print to between 0 and the thickness of the layer of the support on which the relief printing will be carried out, as shown in Figure 5. Thus, if the support used is 5 mm, the printing of any portion of the map will be between 0 and 5 mm, modulo 5 mm, to obtain the expected height of the relief map.

The process of cutting the even and odd numbered layers prepared as described above is applied flush with the lowest print heights (Figure 5) so that the part of the support layer N will serve as a support for the support of layer N+1 (Figure 6).

It should be noted that the height of the support layer should not be too high for 2.5D printing to be possible with Mihaly’s printer (less than 2 to 3 cm) and not too low so as not to multiply the support layers with very thin layers.

The process of cutting the even and odd numbered layers prepared as described above is applied flush with the lowest print heights (Figure 5) so that the part of the support layer N will serve as a support for the support of layer N+1 (Figure 6).

It should be noted that the height of the support layer should not be too high for 2.5D printing to be possible with Mihaly’s printer (less than 2 to 3 cm) and not too low so as not to multiply the support layers with very thin layers.

3.4 Technical choices of realization

In order to apply the principles described above, a first experiment was carried out. Several technical choices on various points were made as mentioned below.

3.4.1 The support

The support must meet different technical requirements due to the manufacturing and operating process. For the global manufacturing process, the support must be compatible with Mihaly’s 2.5D inkjet printing process and with the selected cutting process of the even and odd printing layers. In addition, the support has to meet the stability requirements for the assembly to take place and to withstand the test of time. For the first test, the KAPA® Fix foan panel in 5 mm was chosen.

3.4.2 The order of operations

Once the support has been chosen, a new technical challenge arises concerning the order of operations between printing and cutting. While it might seem logical to perform printing before cutting, this approach risks degrading the print due to the cutting process or could even render cutting impossible. The relief on the support might prevent the passage of the cutting head or the deposit of the plate in reverse.

To simplify the initial experimentation, the decision was made to first perform partial cutting, followed by printing on the pre-cut even and odd layers. It should be noted that the geometrical setting was done visually for the printing which led to some position defects. The reverse order of operations (printing with registration marks and then cutting) is currently being tested.

3.4.3 Printing

For the printing, the only solution allowing to print with heights exceeding 1 mm is the one proposed by the company Mihaly. This solution makes it possible to carry out the printing of the even and odd layers prepared upstream according to the specifications given in 2.4 (to prepare the complete relief and the colour map) and in 3.3 (to prepare the lowered relief of the even and odd layers).

3.4.4 Cutting

Many digital cutting solutions are available, each suited to different material thicknesses and types, including cutters, saws, lasers, hot wires, and water jets. However, the presence of relief ink on the support complicates the cutting process. For the first experiment, the decision was made to cut before printing, and a pre-cutting solution using a cutter was retained (see Figure 7).

It is also important to note that, depending on the chosen cutting method, technical constraints of curvature on the curve delimiting the zones to be cut out can appear.

4. First result

Following the technical choices described above, the cartographic stratoconception was implemented on a map extract of the Reunion Island. Figures 7 to 13 show the different steps to obtain the relief map without height limitation, after assembling the different cut and printed pieces in the manner of a puzzle, which fit perfectly together.

As previously mentioned, the manual setting of the printing on the pre-cut support introduced a slight shift of the printing compared to the cutting which increases locally the visualization of the connection zones.

5. Conclusion

IGN has developed and tested an innovative solution for relief printing without height limitations by hybridizing two French technologies: Stratoconception from CIRTES and color relief printing from Mihaly. The promising results from these tests suggest the potential for establishing an on-demand relief printing service, pending further testing. This solution could meet a significant existing demand from the general public.

6. References

Barlier, C. and Bernard, A., 2020. Fabrication additive – Du prototypage rapide à l’Impression 3D, 2ème édition, Ed. Dunod

Harding C., Hasiuk F., Wood A., 2021. TouchTerrain— 3D Printable Terrain Models. In: ISPRS International Journal of Geo-Information, vol. 10 (3) :108. https://doi.org/ 10.3390/ijgi10030108

Lecordix, F. 2016. Nouvelle dimension pour la sémiologie graphique. In: Cartes & Géomatique, SaintMandé, France, vol. 229-230, pp. 105-115.

Reed, H. P., 1946. The development of terrain model in the war. In: Geographical review, New York, vol. 36, No.4, pp.632-652

Stanley, A. A., 1947. Plastic Relief Models. In: The Military Engineer, Society of American Military Engineers vol. 39, n°261, pp 287–290. http:// www.jstor.org/stable/44567205

Sutter, F., Räber, S., Jenny, B., 2006- 2017, Institute of Cartography and Geoinformation, ETH Zurich, http:// www.terrainmodels.com/contact.html

The paper first appeared in the Proceedings of the International Cartographic Association, 5, 11, 2023.

31st International Cartographic Conference (ICC 2023), 13–18 August 2023, Cape Town, South Africa.

This contribution underwent single-blind peer review based on submitted abstracts. https://doi.org/10.5194/ica-proc-5-11-2023 | © Author(s) 2023. CC BY 4.0 License.

The paper is republished with author’s permission.