PHYSICAL MODELLING OF TERRAIN DIRECTLY FROM SURFER GRID AND ARC/INFO ASCII DATA FORMATS #1

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1 PHYSICAL MODELLING OF TERRAIN DIRECTLY FROM SURFER GRID AND ARC/INFO ASCII DATA FORMATS #1 Y.K. Modi 1*, D.J. de Beer 2 & S. Agrwl 3 1, 3 Deprment of Mechnicl Engineering Jypee University of Engineering nd Technology, M.P., Indi 1 [email protected], 3 [email protected] 2 Technology Trnsfer nd Innovtion Directorte Vl University of Technology, South Afric [email protected] ABSTRACT Additive mnufcturing technology is used to mke physicl models of terrin using GIS surfce dt. Attempts hve been mde to understnd severl other GIS file formts, such s the Surfer grid nd the ARC/INFO ASCII grid. The surfce of the terrin in these file formts hs been converted into n STL file formt tht is suitble for dditive mnufcturing. The STL surfce is converted into 3D model by mking the wlls nd the bse. In this pper, the terrin modelling work hs been extended to severl other widelyused GIS file formts. Terrin models cn be creted in less time nd t less cost, nd intricte geometries of terrin cn be creted with ese nd gret ccurcy. OPSOMMING Lgvervrdigingstegnologie word gebruik om fisiese modelle vn terreine vnf GIS oppervlkdt te mk. Dr is gepoog om verskeie nder GIS lêerformte, soos die Surfer rooster en die ARC/INFO ASCII rooster, te verstn. Die oppervlk vn die terrein in hierdie lêerformte is omgeskkel in 'n STL lêerformt wt geskik is vir lgvervrdiging. Verder is die STL oppervlk omgeskkel in 'n 3D model deur die knte en die bsis te modelleer. In hierdie rtikel is die terreinmodelleringswerk uitgebrei n verskeie nder lgemeen gebruikte GIS lêerformte. Terreinmodelle kn so geskep word in korter tyd en teen ler koste, terwyl komplekse geometrieë vn terreine met gemk en groot kkurtheid geskep kn word. 1 # This rticle is n extended version of pper presented t the 2011 RAPDASA conference. * Corresponding uthor. South Africn Journl of Industril Engineering, July 2012, Vol 23 (2): pp

2 1. INTRODUCTION The dt of terrin represents surfce. There re severl GIS dt formts in which the dt of terrin is vilble. However, it contins just points on the terrin surfce, nd does not include 3D informtion. Mny pplictions require physicl model of terrin. Some of these pplictions re ctchment modelling, town plnning, lndscpe rchitecture, conservtion mngement, nd militry strtegy plnning. A terrin model helps with visulistion, presenttion, nd community eduction, nd serves s very effective tool for wtershed nd geologicl eduction. Additive mnufcturing (AM) mkes models nd prototypes in less time nd t less cost thn conventionl prototyping techniques. The AM process cn even mke complicted prts in mtter of hours. It tkes the solid model of prt s its input, nd fbrictes the prt lyer by lyer without using tools or fixtures. A model cn be mde out of ABS (crylonitrile butdiene styrene, tough plstic), polycrbontes, nylon, snd, metl, etc. Intricte geometries of terrin cn be reproduced esily nd more ccurtely using the AM process. The file formt vilble for dditive mnufcturing is STL. The GIS dt of terrin needs to be trnslted into STL for dditive mnufcturing, so tht the STL file cn be downloded to n AM mchine for pre-processing nd fbriction. Reserchers hve used different methods to mke physicl model of terrin with AM using GIS dt. Most of them hve used commercil softwre nd severl trnsltion steps to convert the surfce dt into 3D STL prts. Rse [18] converted GIS dt into VRML formt using his progrm; but he did not discuss the GIS file formt used. Jcobs [15] converted the GIS dt into DXF file formt using Lnd Desktop; the DXF file is then converted into n STL prt using Mgics RP softwre. Mueller [16] mde terrin models with AM technology using SDTS dt. He used meshing lgorithm, such s Greeds insertion, to get mesh from n elevtion grid. The mesh dt ws then trnslted into STL nd PLY formt. Biley [3] creted physicl models of the October 2003 fires in Southern Cliforni, using US mps bsed on stellite dt. However, the uthor did not specify the dt formt he used s input. Agrwl et l. [1] converted DEM ASCII XYZ dt into the STL file formt using Globl Mpper. This STL surfce ws then imported into Mgics RP to obtin 3D prt. Colour 3D Printer from Z Corportion is the first AM process to incorporte the bility to print full-colour prt [11, 21]. AM technology hs lso been used to fbricte rchitecturl models [12, 7]. Cmpbell et l. [4] hve reviewed the use of AM technology for terrin modelling, rchitecturl modelling, nd other pplictions in South Afric. Frnic et l. [8] hve provided wy to mke physicl model of city using digitl terrin model (DTM), photogrmmetric mpping, nd true orthophoto s input dt. They mde model of the city of Zgreb in Croti. Rse [19] hs reported building coloured physicl models of city nd lndscpe with relief. He lso mde physicl models to represent demogrphic nd socio-economic dt. A continuous surfce for representing the demogrphic dt ws obtined by interpolting points or polygon dt using the pycnophylctic interpoltion method. He used ESRI ArcGIS softwre to prepre the bsic dt, nd his own computer progrm for interpoltion. The methods used by the bove reserchers for terrin modelling involved severl softwre tools. They obtined 3D STL prt in severl steps: the methods were not direct, nd dt loss took plce when trnslting to intermedite file formts. Severl commercil softwre progrms exist to trnslte GIS dt into STL formt [9, 14]. However, none of them trnsltes directly to 3D STL file: they produce n STL surfce. Agrwl et l. [2] developed wy to convert DEM ASCII XYZ dt directly to 3D STL prt, nd mde softwre tool for the conversion. 231

3 In the present reserch, the work of Agrwl et l. [2] hs been extended to other widelyused dt formts. The softwre issue in converting DEM ASCII XYZ dt of size lrger thn 90x100 hs been tken cre of. The ARC/INFO ASCII dt formt is the sme s the DEM ASCII XYZ dt formt. Functions hve been written into the progrm to convert the Surfer grid file formt. The method developed by Agrwl et l. hs been used to mke the tringles in the top surfce, wlls, nd bse of the 3D STL prt. In Surfer grid formt, the missing elevtion vlues in the grid re not explicitly specified; so wy hs been developed to identify the missing elevtion vlues in the grid. 3D STL prts hve been obtined for smple Surfer grid files, nd loded successfully in Pro/E for disply. 2. ARC/ INFO ASCII AND DEM ASCII XYZ DATA FORMATS The ARC/INFO ASCII dt formt is used by ARC/INFO, GIS progrm by ESRI Corportion; the file uses the extensions ASC, FIG, AGR, or GRD. The ARC/INFO ASCII dt formt is the sme s the DEM ASCII XYZ dt formt, trnslted into 3D STL prts by Agrwl et l. [2]. This formt hs heder consisting of six records: these specify the geogrphic domin nd resolution, then the elevtion vlues of grid cells. The elevtion vlues re given in grid of size nrows x ncols in both dt formts. Work on the DEM ASCII XYZ dt ws extended to incorporte lrge mount of dt. Turbo C++ softwre, with the set of prmeters used, ws not ble to hndle DEM dt lrger thn 90x100. The sme C progrm ws compiled nd executed in Visul C++, nd it could run successfully in Visul C++ with lrger file size. The progrm ws used to trnslte the DEM dt of Tble Mountin, the Swrtberg Mountin rnge, the Welbedcht region, nd Nvl Hill in Bloemfontein, South Afric into 3D STL prts. The dt size rnged from 400x400 to 1200x1200. The size of the STL files rnged from 60 MB to 740 MB. A solid modeller like Pro/E successfully opened moderte-sized files, such s tht of Tble Mountin. However, it hd memory issues when opening STL files of 700 MB with the current set of environment vribles. Prmeters such s proe_memory_buffer_size needed to be ltered to void memory error. This is being explored. Figure 1 shows the STL file of Tble Mountin in Cpe Town, South Afric loded in Pro/E. The DEM ASCII XYZ dt of Tble Mountin hs only the dt of the terrin surfce. This terrin dt ws converted into n STL surfce; the wlls nd bse were dded to it, nd the 3D STL prt of Tble Mountin shown here ws obtined. Figure 1: STL prt of Tble Mountin loded in Pro/E 3. SURFER GRID FILE FORMAT Surfer grid is widely-used GIS file formt, nd is extensively used by surfce gridding nd contouring progrms in the erth sciences. The Surfer grid dt formt is s follows: 232

4 DSAA ncolumns mrows xmin xmx ymin ymx zmin zmx el11 el12 el13 el1n el21 el22 el23 el2n elm1 elm2 elm3 elmn The file formt consists of heder followed by grid of elevtion vlues [20, 17]. There is dt formt identifier in the first line of the heder. (DSAA stnds for Dt in Surfer grid ASCII formt, nd DSBB stnds for Dt in Surfer grid binry formt). It is followed by the number of columns nd rows of points in the grid. The third line contins the minimum nd mximum vlues of x-coordintes in the grid. The next line contins the minimum nd mximum vlues of the y-coordintes. The cells re regulrly spced in the x-direction nd the y-direction. The cell size in x- nd y-directions is clculted from their minimum nd mximum vlues. This is different from the DEM ASCII XYZ formt, where the cell size is explicitly given. The fifth nd lst line of the heder contins the minimum nd mximum vlues of elevtion in the grid. The DEM ASCII XYZ formt gives the NODATA_vlue in the heder. It corresponds to dt tht is missing in the grid. In Surfer grid formt, the NODATA_vlue is not explicitly specified in the heder. The Surfer grid formt is interpreted for missing dt s follows. Any vlue beyond the rnge of minimum nd mximum elevtion vlues is considered to be missing dt. For exmple, very high elevtion vlue of E+038 meters in the dt for terrin on erth is considered to be missing dt. Geosptil Designs nd Globl Mpper lso discuss the Surfer grid dt formt [10, 13]. There re missing dt in the elevtion grid due to inherent inccurcies in remote sensing or surveying methods tht re used to obtin the dt. They lso depend on the ground plnimetric reference system used, such s UTM, geogrphic, or the stte plne coordinte system. A qudrngle of net lines, or block, hs profiles with n unequl number of elevtion vlues. In order to find missing dt vlues in the elevtion grid, the C progrm scns ll the cells in the grid. A constnt NODATA_vlue with lrge negtive integer vlue is declred. Those cells in the grid tht hve elevtion vlues beyond the rnge of minimum nd mximum vlues re ssigned NODATA_vlue. This is similr to the NODATA_vlue lredy present in the DEM ASCII XYZ dt. The minimum elevtion vlue is directly vilble in Surfer grid formt, s discussed erlier. This vlue therefore need not be computed to clculte the bse of the STL prt, s is done for DEM ASCII XYZ dt. The bse of the STL prt is computed by subtrcting the required wll height from the minimum elevtion vlue. The intervls in x- nd y-directions re different, nd re computed from the vlues in the heder. The first row of elevtion vlues tht follows the heder of the file represents the southern edge of the grid, in contrst to the DEM ASCII XYZ dt where it is the northern edge [20]. This is nother mjor devition from the DEM ASCII XYZ formt. 233

5 Figure 2: Tringles in the STL prt for two consecutive rows The input Surfer grid dt file is red by the C progrm. The elevtion vlues re red in mtrix, nd the differences bove re tken cre of. The dt is trnslted in mnner similr to tht for DEM ASCII dt [2]. A 3D STL prt of terrin is mde by mking tringles for two consecutive rows or columns t time, s discussed by Agrwl et l. [2]. If the STL prt is built by proceeding long the x-direction, the tringles re built for two consecutive rows, s shown in Figure 2. For two consecutive rows, the tringles on the top represent the surfce of the terrin. The left wll, the right wll, nd the bse re mde. The front nd rer wlls re mde only for the portion needed. Figure 3 shows the tringles mde for two consecutive columns when the STL prt is built by proceeding in the y-direction. Figure 3: Tringles in the STL prt for two consecutive columns If the Surfer grid represents 2D solids seprted by rows, the prt is built by proceeding in the x-direction fter removing singulrities. However, if it represents 2D solids seprted by columns, the prt is built by proceeding in the y-direction. If the dt hs gp inside it, nd the user input is ffirmtive for interpoltion, the dt is interpolted nd the prt is built in the x-direction. If the user does not wnt to interpolte, then n STL prt cnnot be built in the event of gp; so n STL surfce is mde in this cse. This cn hve visul vlue, nd the user my like to run the progrm gin with interpoltion. 234

6 The C progrm ws run for smple Surfer grid dt. The progrm successfully converted the surfce dt into 3D STL prts. Consider the Surfer grid file SS1.GRD with four elevtion vlues, ech equl to DSAA SS1.GRD The dt hs two columns nd two rows. The cell size is 30. The minimum nd mximum elevtion vlues re 30. The STL prt is mde with wll height of 30. This gives cube with sides of 30, nd hving centrl digonl with opposite ends t (0, 0, 0) nd (30, 30, 30). Figure 4 shows the STL prt of the smple dt in Surfer grid formt. This Surfer grid file is converted to n STL file clled SS1.STL. The cube hs six fces, ech mde with two tringulr fcets in the STL file. Therefore, there should be 12 fcets in the STL file. The STL file SS1.STL is s follows: SS1.STL solid output fcet norml vertex vertex vertex endfcet fcet norml vertex vertex vertex endfcet fcet norml vertex vertex vertex endfcet fcet norml vertex vertex vertex endfcet fcet norml vertex vertex vertex endfcet fcet norml vertex

7 endsolid vertex vertex endfcet fcet norml vertex vertex vertex endfcet fcet norml vertex vertex vertex endfcet fcet norml vertex vertex vertex endfcet fcet norml vertex vertex vertex endfcet fcet norml vertex vertex vertex endfcet fcet norml vertex vertex vertex endfcet As cn be seen, the STL file hs 12 fcets. It is lso pprent tht the vertices of the tringles re one of the vertices of the cube with the centrl digonl hving opposite ends t (0, 0, 0) nd (30, 30, 30). Therefore, the dt is being converted ccurtely without ny loss in trnsltion. The x-coordinte, y-coordinte, nd the elevtion vlues from the Surfer grid file re used directly to mke the vertices of the tringle. There is therefore no dt loss in conversion. The STL file obtined for terrin model in cube form lso shows this. Figure 5 shows the STL prt obtined fter the conversion of smple 2 of the Surfer grid dt. This lso hs four elevtion vlues. However, the four elevtion vlues re not equl. Figure 6 shows the STL prt for smple 3 of the Surfer grid dt clled SS3.GRD. A typicl exmple is creted here with severl no-dt vlues. The shpe of the vlid dt vlues is correctly produced The STL file verifies tht the elevtion vlues go directly into the vertices of the tringles. It should be noted while viewing the STL prt in Figure 6 tht the first row of elevtion vlues in SS3.GRD goes to the front of the STL prt. 236

8 Figure 4: STL prt of smple 1 Surfer grid loded in Pro/E Figure 5: STL prt of smple 2 Surfer grid loded in Pro/E Figure 6: STL prt of smple 3 Surfer grid loded in Pro/E 237

9 SS3.GRD DSAA E E E E E E E E E E E E E E E E+038 Figure 7 shows the STL prt of smple 4 of the Surfer grid dt. Here there were gps between vlid elevtion vlues in the x-direction. The C progrm correctly mde the STL prt by proceeding in y-direction. When viewed, the STL prt verifies tht the conversion is ccurte. The dimensions were verified in the Pro/E softwre. However, scles or dimensions could not be shown in the Figures. The ccurcy of the conversion is verified by observing the coordintes of vertices of tringles in the STL file (e.g., SS1.STL, given erlier). Figure 7: STL prt of smple 4 Surfer grid loded in Pro/E Figure 8 shows the STL prt of smple 5 in Surfer grid formt. The dt hs 10 columns nd 14 rows. The grid vlues lie in the rnge (min = 11.2, mx = 19.4). The Surfer grid dt is shown in Appendix I. There re mny no-dt vlues in the dt. The dt vlue tht lies beyond the rnge (11.2, 19.4) is no-dt vlue. Therefore E+038 in the dt is no-dt vlue. The front fce in Figure 8 represents the first row with nine vlid dt vlues, while the rer fce of the STL prt in Figure 8 shows the 14 th row hving five vlid dt vlues. Due to the presence of no-dt vlues, the bse of the 10 cols x 14 rows dt is not rectngle. 238 Figure 8: STL prt of smple 5 Surfer grid loded in Pro/E

10 Figure 9 shows the STL prt of smple 6 Surfer grid dt. The dt hs 11 columns nd 18 rows, nd elevtion vlues re in the rnge min = -1.00, mx = The terrin hs severl peks nd steep slopes. Figure 9: STL prt of smple 6 Surfer grid loded in Pro/E The dt contined in Figures 8 nd 9 re just smple dt. The progrm is ble to tke cre of the Surfer grid of ny terrin with lrge grid, s ws done with the DEM ASCII XYZ dt. 4. FUTURE SCOPE Sometimes the size of the STL file becomes very lrge. For exmple, for n elevtion grid of 1200x1400, the number of tringles is round 3.2 million. The user my wnt to hve the option to decrese the number of tringles nd hve smller STL file for exmple, when ccurcy is not importnt nd the AM prt is needed minly for visulistion purposes. A smller STL file will decrese the pre-processing nd prt-building time in AM. One wy to decrese the number of tringles could be to fit curve on ech row of the grid, nd to find elevtion vlues on this curve t lrger intervl. The uthors lso pln to investigte the memory error in Pro/E by ltering the prmeters such s proe_memory_buffer_size, nd then loding lrge STL files. The uthors pln to extend this work to include other widely-used GIS dt formts such s USGS DEM dt. 5. CONCLUSIONS A method hs been developed to convert the dt of terrin in Surfer grid formt to 3D STL prt. Functions hve been dded nd modified in the C progrm. Smple Surfer grids hve been tken, nd the conversion hs been verified. The 3D STL prts were loded in Pro/E for visulistion. A softwre issue in converting lrge DEM ASCII XYZ dt ws delt with. The dt of terrin surfce in Surfer grid formt hs been directly converted into 3D STL prt. There ws no trnsltion to n intermedite file formt, nd therefore no dt loss ws ssocited with n intermedite file formt. The STL file cn be downloded to n AM mchine to grow terrin model. Intricte geometries of terrin cn be creted with ese nd ccurcy. 239

11 REFERENCES [1] Agrwl, S., Antunes, J.P., Theron, E., Truscott, M. & de Beer, D.J Physicl modeling of ctchment re by rpid prototyping using GIS dt, Rpid Prototyping Journl, 12(2), [2] Agrwl, S., de Beer, D.J. & Modi, Y.K Direct conversion of GIS surfce dt to 3D STL prt for terrin modelling by dditive mnufcturing technologies, 11 th Annul Interntionl RAPDASA conference, VUT, Vnderbijlprk, South Afric. [3] Biley, M Lyered mnufcturing for scientific visuliztion, Communictions of the ACM, 48(6), [4] Cmpbell, R.I., de Beer, D.J. & Pei, E Additive mnufcturing in South Afric: Building on the foundtions, Rpid Prototyping Journl, 17(2), [5] Climte Source Arc/Info ASCII grid files. formt/rc_sciigrid.html. Accessed August [6] Codehus ArcInfo ASCII grid formt. GEOTOOLS/ArcInfo+ASCII+Grid+formt. Accessed August [7] De Beer, D.J., Brnrd, L.J. & Booysen, G.J Three dimensionl plotting s visuliztion id for rchitecturl use, Rpid Prototyping Journl, 10 (2), [8] Frnic, S., Bcic-Deprto, I. & Novkovic, I D model nd scle model of the city of Zgreb, Qulity scle nd nlysis spects of city models, in Proc. ISPRS Technicl Commission IV Symposium XXXVIII/2-W11/Frnic_Novkovic_Bcic-Deprto.pdf. Accessed August [9] Geo Community Accessed August [10] Geosptil Designs Surfer 6 grid file formt. Accessed August [11] Gibson, I. & Ming, L.W Colour RP, Rpid Prototyping Journl, 7(4), [12] Gibson, I., Kvn, T. & Ming, L.W Rpid prototyping for rchitecturl models, Rpid Prototyping Journl, 8(2) [13] Globl Mpper Surfer Grid (ASCII nd binry formt files). _Formt_Files. Accessed August [14] Grime Accessed August [15] Jcobs, L.D Terrin modeling using rpid prototyping. edu/cdemics/reserch_centers/reu/pdf/2003/terrin%20modeling%20using%20rpid%20prot otyping.pdf. Accessed August [16] Mueller, J Terrin modeling using solid freeform surfces. edu/cdemics/reserch_centers/reu/pdf/2004/terrin%20modeling%20using%20solid%20freef orm%20fbriction.pdf. Accessed August [17] OcenTecher Digitl Librry Grids. Accessed August [18] Rse, W.-D Physicl models of GIS objects by rpid prototyping, Geosptil theory, processing nd pplictions, In Proc. ISPRS Technicl Commission IV Symposium 2002, The Interntionl Archives of the Photogrmmetry, Remote Sensing nd Sptil Informtion Sciences, GITC, The Netherlnds, org/proceedings/xxxiv/prt4/pdfppers/237.pdf. Accessed August [19] Rse, W.-D Visuliztion of three-dimensionl GIS objects using rpid prototyping technology, in Proc. GeoViz, Hmburg, Germny. VisuliztionGISObjects.pdf. Accessed August [20] Sheriff, S.D Surfer Grids, ids.pdf. Accessed August [21] Z Corportion Accessed August

12 Appendix I Surfer grid file of dt in smple 5, hving 10 cols x 14 rows 241