Global Mapper v25.0

DEM DTM to CAD CAM CNC?

BlueFin
BlueFin Global Mapper UserTrusted User
edited November 2009 in Elevation Data
I am looking for a way to obtain 3D elevation data for given areas of choice (a 10 mile square for example), and once the data is cropped to the area needed then export to a file format that can be read by CAD/CAM software. Generally speaking the .STL format is the most common. This would allow the data to be opened in a 3D CAM application to generate a toolpath for a CNC machine (a wood router). This would facilitate the creation of wooden topography models of the earths terrain. Would GM be suited for this type of work in regards to the file export?

Also it may be needed to exaggerate the height of the data to make the peaks more pronounced, is this possible in GM or would it have to be done elswhere?

Thanks

Comments

  • global_mapper
    global_mapper Administrator
    edited November 2009
    You can absolutely use Global Mapper for this. You can either load your own terrain data, or simply pull in NED (for the US) or SRTM (worldwide) elevation data using the File->Download Online Imagery/Data menu command. Then you can simply export to your desired format, such as the STL format or perhaps a DXF mesh file, using the File->Export Raster and Elevation Data menu.

    If you need to exaggerate the height values what you can do prior to export is open the Control Center, select your elevation layer(s), press Options, then go to the Adjust Elevations tab and specify a scale factor equivalent to your desired exaggeration. Then just do the export normally after that to get the exaggerated elevations applied.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • BlueFin
    BlueFin Global Mapper User Trusted User
    edited November 2009
    Wow, thanks for the fast reply. When I have some time over the next months holidays I will give this a try.
  • BlueFin
    BlueFin Global Mapper User Trusted User
    edited November 2009
    I am trying out GM's .STL output of DEM data and was able to get it into my machining software, but the size of the file ends up being 3,240 feet wide when I try to generate a tool path. That is a bit big for my machine to handle :) how can I define an output to something like 6 inches square instead?

    Tyson
  • global_mapper
    global_mapper Administrator
    edited November 2009
    Tyson,

    When you export the STL file there should be a Point Offset/Scale tab that will allow you to scale the values down to the size that you need. Just use the same scale value (like 0.000154321 to make 3240 feet 6 inches across) for X, Y, and Z to keep them the same relative to each other.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • BlueFin
    BlueFin Global Mapper User Trusted User
    edited November 2009
    Global Mapper,

    Been doing some testing, have not been able to export a usable file so far, here are some numbers that I came up with. I am not sure if I need to be doing something different, or if there is something going on with the math in GM.

    I selected a small area of DEM data from a local mountain top. I used the export function to export 5 files of the same exact area in 5 different scales. I kept the XYZ scaling the same across each entry, and used vertical units of an inch each time. The .STL files turned out like this when loaded into my CAM software that reads them:

    1, scale 1, 2.28 MB, x8328", y6484", 12600 triangles
    2, scale .1, 2.17 MB, x833", y648", 12600 triangles
    3, scale .01, 2.06 MB, x83", y65", 12525 triangles
    4, scale .001, 1.95 MB, x9", y7", 2235 triangles
    5, scale .0001, 1.84 MB, x1", y1", 175 triangles

    As you can see when scaling below .01 the number of triangles is affect severely and the shape becomes degraded (totally), at .0001 even though it indicates 175 triangles it will only display one flat square. If I try to export at .00001 or less the file won't open in CAM, just freezes the program.

    Tyson.
  • global_mapper
    global_mapper Administrator
    edited November 2009
    Tyson,

    I took a look and found that Global Mapper was using a fixed number of decimal places for the X and Y coordinates in the STL export, so with a small scaling factor a lot of relative accuracy could be lost. I have updated the exported to use more precision when small scaling factors are used, which should improve your results.

    I have placed a new build at http://www.globalmapper.com/global_mapper11.zip with the change for you to try. Simply download that file and extract the contents into your existing v11.xx installation folder to give it a try. If you are using the 64-bit v11 version there is a new build at http://www.globalmapper.com/global_mapper11_64bit.zip .

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • BlueFin
    BlueFin Global Mapper User Trusted User
    edited November 2009
    Mike, I installed the new file and tried it out, however the results seem to be the same here. At .01 scale and above I had the proper shape and 10,700 triangles, as soon as I tried a .001 scale the shape geometry dimensions 8" x 7" was correct, but the triangle count went down to 1700 and the shape was a bunch of blocks stacked up to sort of make the shape of the mountain.

    Tyson
  • global_mapper
    global_mapper Administrator
    edited November 2009
    Tyson,

    Can you zip up one of the resulting files with a small scale and post it here or email it to support@globalmapper.com so that I can take a look? It could be either that even more precision is needed from Global Mapper or that the CAD/CAM software can't handle such small values close together. Is there perhaps some scaling method in the CAD/CAM software? I don't believe most other STL users have had to do this kind of scaling.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com