Terrain Relief Models, Unabridged

How To
2

Software Choices and Setup

For creating terrain relief models, you will need to make a few software choices. Some of them are basically fait accompli – there’s effectively no alternative to QGIS that does not involve departing completely from this writeup (which you are, of course, free to do). Others are down to preference or availability – if you have a MeshCAM or Vectric Aspire license, there’s a good chance you might want to go that way with the CAM parts of the workflow. I’ve broken the software into three groups: software for processing the source GIS data (i.e. QGIS), software for machining terrain relief models, and software for engraving trails onto terrain relief models (which is completely optional, of course).

Processing the source data:

  • QGIS – Free and open source Geographic Information System software used for processing elevation data.
    • Heightmap Export plugin – QGIS plugin for easily exporting elevation data as high-resolution 16-bit PNG heightmaps.
  • Inkscape – Everyone’s favorite free and open source vector drawing program. In this case, used to take trails exported from QGIS as DXF files and turn them into properly rescaled usable SVGs (for engraving on your model or carving a companion map).

Machining your terrain model (choose any):

  • Image 2 Surface Add-In for Fusion 360 – Free and open source add-in to Fusion 360, but Fusion 360 does not handle large, high-resolution models well (if at all).
  • PixelCNC – Inexpensive (~$75) software for CNC from image (or STL) files. (Still some annoying quirks at its current version 1.33a, but very fast processing and very nice end results.)
  • Vectric PhotoVCarve – Somewhat more expensive (~$150) software that can carve based on a greyscale heightmap, but constraints make it a poor fit for terrain models (e.g. it does not appear you can make separate roughing and finishing jobs with different tools or use tapered endmills).
  • MeshCAM Standard – More expensive (~$250) software that really can handle STL files and heightmaps, and is included with the Nomad.
    • MeshCAM v6 was significantly slower (9 minutes vs. 14 seconds) generating toolpaths for my test project than PixelCNC, but the output looked reasonable.
    • MeshCAM v7 took 2.5 hours to generate an order of magnitude longer G-code. As that’s so far out of family compared to the others, my assumption would be that I was doing something poorly.
  • Vectric Aspire – Extremely expensive (~$2000) software that can use heightmap images. (I have not even bothered downloading the trial for Aspire, as it’s priced utterly out of my pure hobbyist reach.)

The general scale of my usual projects is something like a high-resolution model of an area about 10km square at a 1/3 arc-second resolution. That’s on the order of 1000x1000 samples, putting it well above what I’ve found Fusion 360 will handle. I’ve had excellent results with PixelCNC. While it is not without its quirks and limitations, unless you already have one of the expensive options or have requirements that preclude it from fitting into your workflow, PixelCNC would generally have my recommendation. I do not have access to MeshCAM or Vectric Aspire, but if you do and you would like to document the respective workflows in one or more of them, it would be interesting and likely helpful to add that information to this collection of documentation.

Engraving trails onto a terrain relief model (choose any):

  • PathTracer (part of the Heightmap Export plugin in QGIS) – Simple, but capable of making a brute-force mapping of SVG path data onto PNG heightmap data.
  • Autoleveller – Designed for PCB engraving, but exporting the heightmap data into a format it can parse may allow you to map flat toolpaths created from the SVG path data onto the 3D surface. (I’m planning to look into it, as the potential for trading light-but-bodged for heavy-but-smooth is intriguing.)
  • Fusion 360 – I have no idea how this would work, but someone indicated they used it successfully.
  • Vectric something-or-other – From reading meager marketing materials, I get the feeling like something might be possible, but I remain priced out of that market.

This part of the process should be ripe for enhancement, but for now, I at least have a workflow that produces the desired results, even if it is a little bodged.

Installing QGIS

  1. Go to https://www.qgis.org/ then click over to download page.
  2. Look down the page to find the section for standalone installers. The latest version should serve you well (or use the long term release if you’re super conservative). All these instructions are now based on the version 3 family, so don’t hunt down the downloads for the old versions that started with a 2.
  3. Click the appropriate link (hopefully 64-bit these days) to start the QGIS download.
  4. Run the installer you’ve just downloaded. The defaults should be cromulent, so you can just next-next-next through it.
  5. Open QGIS from the shortcut icon named QGIS Desktop 3.6.4 (or whatever version number you’ve just installed).
  6. From the Plugins menu, choose Manage and Install Plugins...
  7. On the left side, choose All.
  8. In the search box, type Heightmap Export (or at least the first few letters) to find the Heightmap Export plugin.
  9. Select the plugin, then click the Install Plugin button.
  10. Close the plugins dialog.
  11. You should now have a Heightmap Export menu option under the Raster menu. If you see it there, you have successfully installed QGIS and the plugin.
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