"Where's that?"
"On Mars. NASA might land the next rover there. Can't you just find a model and print it? I need it for science tomorrow. We're doing group projects."
"On Mars. NASA might land the next rover there. Can't you just find a model and print it? I need it for science tomorrow. We're doing group projects."
A quick check on Thingiverse revealed no such model - not surprising. This presents quite the dilemma: Let the boy learn a lesson not to procrastinate or work on a really cool 3D printing project? The project was too cool to pass up but I have a tiny bit of guilt enabling the boy's poor planning.
Two problems to tackle first. Where is Syrtis Major and where do I get elevation data? The latter turns out to be really easy. I remember when NASA mapped Mars with a laser altimeter. A little googling and I find a digital elevation model downloadable as a TIFF file. Next problem is locating Syrtis Major. Some more googling and I download a nice paper with an image and latitude/longitude values. The candidate landing site in NE Srytis is topographically boring (i.e., flat) for obvious reasons. But the whole Srytis Major province is perched 3 miles above Isidis Planitia and a 2000-mile diagonal map is dramatic. That's what we'll target.
I wrote a Matlab script (see below) to read in the TIFF file, subset out the area, smooth and decimate the surface down to something manageable. Someone wrote a nice mesh to STL exporter. My first crack at it would take 32 hours to print and since this is a fire fighting exercise, I smoothed it down even more and made the model only 6" on a side to get a 14 hour predicted print time. Right about when the school bus comes. The horizontal scale is 16,000,000:1 and the vertical is 220,000:1, which is about a 70x exaggeration in the elevation.
In my experience, many 3D models have errors so they are not manifold. Windows 10 has a built in app called 3D Builder that is great at correcting errors. I usually run my STL files through it before trying to slice them for printing. Here's a rendering of the model in 3D Builder:
In my experience, many 3D models have errors so they are not manifold. Windows 10 has a built in app called 3D Builder that is great at correcting errors. I usually run my STL files through it before trying to slice them for printing. Here's a rendering of the model in 3D Builder:
Matlab script to generate the source STL file:
%% a=imread('Mars_MGS_MOLA_DEM_mosaic_global_463m.tiff');; %% maps % https://astrogeology.usgs.gov/search/details/Mars/GlobalSurveyor/MOLA/Mars_MGS_MOLA_DEM_mosaic_global_463m/cub % Minimum Latitude -90 % Maximum Latitude 90 % Minimum Longitude -180 % Maximum Longitude 180 % Direct Spatial Reference Method Raster % Object Type Pixel % Lines (pixels) 23040 % Samples (pixels) 46080 % Bit Type 16 % Radius A 3396000 % Radius C 3396000 % Bands 1 % Pixel Resolution (meters/pixel) 463.0836 % Scale (pixels/degree) 128 % Horizontal Coordinate System Units Meters % Map Projection Name Simple Cylindrical % Latitude Type Planetocentric % Longitude Direction Positive East % Longitude Domain -180 to 180 imshow(a(1:100:end,1:100:end)) %% subset % http://onlinelibrary.wiley.com/doi/10.1029/2003JE002143/abstract % http://www.planetary.brown.edu/pdfs/2763.pdf % Figure 1: The map covers an area from -10S to 30N and from 270W to 315W. % 270 W is -90 E and 315 W is -45 E lat=linspace(-90,90,size(a,1)); lon=linspace(-180,180,size(a,2)); x=interp1(lat,1:size(a,1),-[30 -10],'nearest'); y=interp1(lon,1:size(a,2),-[-45 -90],'nearest'); b=a(x(1):x(2),y(1):y(2)); %% figure N=5; pcolor(flipud(b(1:N:end,1:N:end))) shading flat %% smooth S=25; c = double(imgaussfilt(b,S)); %% plot figure N=2*S; mesh((c(1:N:end,1:N:end))) shading flat %% make surface to export N=2*S; d=c(1:N:end,1:N:end); d=d-min(d(:)); d(d<0)=0; d(1:end,1)=0; d(1:end,end)=0; d(1,1:end)=0; d(end,1:end)=0; d=d*35/max(d(:)); [u,v]=meshgrid(1:size(d,2),1:size(d,1)); u=u*150/max(u(:)); v=v*150/max(v(:)); %% mesh(u,v,d); axis equal %% export % https://www.mathworks.com/matlabcentral/fileexchange/20922-stlwrite-filename--varargin- stlwrite('mars4.stl',u,v,d)
