Process for generating CNC maps using QGIS

cnc_maps_process.md

Data Download

DEM (terrain, raster) data

• Get DEM files from National Map download tool
  • https://viewer.nationalmap.gov/basic/#/
• Set Area of Interest: Selectable Polygon -> Select... -> US State or Territory
  • then click a state on map to select it
• Or Set Area of Interest: Map Extent/Geometry -> Click Extent -> Draw a rectangle on map
• After area selected, search for:
  • Elevation Products (3DEP) -> 1/3 arc-second or 1 arc second
• Click search products
• Download TIF Files manually OR...
  • Click TXT icon to download text file with list of data URLs
  • remove all lines that are not tifs manually or with regex: ^((?!.tif$).)*$\n
  • install and open uGet (https://sourceforge.net/projects/urlget/)
  • File -> Batch -> Open TXT File
  • Use "Mark By Filter..." to filter & only download TIF files

State outlines

• Need shapefiles - vector representation of state outlines or outlines of map boundary etc.
• Get state shapefiles from: https://www.census.gov/geographies/mapping-files/time-series/geo/carto-boundary-file.html https://www2.census.gov/geo/tiger/GENZ2018/shp/cb_2018_us_state_500k.zip

Data Transformation

Split state outlines (vectors) into separate files

• The file cb_2018_us_state_500k has all states - need to split into several files
• Create QGIS Project
• Add vector layer -> cb_2018_us_state_500k.shx (state outlines downloaded above)
• Vector -> Data Management Tools -> Split Vector Layer & set NAME as unique ID field

Merge state DEM files

• Drag all the TIF files downloaded above into QGIS
• Raster -> Misc -> Merge
• Select all layers, set High Compression and save to file

Reproject to final CRS

• Decide on a projection - ESRI:102003 is good for US states (Albers Contiguous US)
• Reproject merged raster layer in QGIS: Raster -> Projections -> Warp (reproject)
• Enter desired target CRS

Downscale raster

• If size is unmanageable, downscale at this step
• (ie. after reproject, ideally, because reproject loses resolution)
• Raster -> Raster calculator -> modify # of rows/columns

Raster terrain exaggeration

• DEMto3D supports exaggeration up to 10x
• If you want more than that, precalculate it here with raster calculator
• Raster -> Raster Calculator -> "layer@1" * 5 (for 5x exaggeration)

Reproject vector layer

• Add state outline vector to project
• Vector -> Data management -> Reproject
• set target to same projection as raster

trim terrain tiles to vector outline

• Add state file from above as a new vector layer in same project as raster data
• Raster -> Extraction -> Clip by Mask layer
• Select mask (state vector) and raster (combined terrain) layers, set high compression, save to file

Export as image

• Open clipped file from above in new QGIS project, or hide/remove other layers
• Confirm your CRS setting (USA_Contiguous_Albers_Equal_Area_Conic or desired projection)
• Set project background color to black
• Set terrain layer min to 0 (sea level) or whatever you want
• Project -> Import/Export -> Export map to image

Merged/Clipped raster to G-code

Option 1 - PixelCNC

• Can import raster data directly into PixelCNC and generate G-code
• However, as of now (v1.43) PixelCNC does not have a post-processor for Easel
• Coming soon in v1.44
• Could use standard GRBL post with different G-code sender (Candle, UGS)

Option 2 - DEMto3D to Fusion 360 to G-code

• Install QGIS DEMto3D plugin using QGIS Plugin Manager

 // didn't take detailed notes on using DEMto3D - but this is my preferred method
 // read the DEMto3D docs and tweak settings to your liking
 // consider terrain exaggeration - anything more than ~6-7x exaggeration looks implausibly spiky