Artistic Terrain Commands and Notes

artistic_terrain_resources.md

Resources and Links

Inspiration and people I've learned from

• Brandon Plewe: https://carto.byu.edu
• Tom Patterson: http://www.shadedrelief.com/
• John Nelson: https://adventuresinmapping.com/
• Kenneth Field: http://cartonerd.blogspot.com/
• Daniel Huffman: https://somethingaboutmaps.wordpress.com/

Esri Terrain Tools

• https://www.esri.com/arcgis-blog/products/3d-gis/3d-gis/terrain-tools-1-1-released/

GDAL docs

• https://gdal.org/programs/index.html#raster-programs

Conda getting started docs

• https://docs.conda.io/projects/conda/en/latest/user-guide/getting-started.html

Topographic Position Index (TPI)

• http://www.jennessent.com/downloads/TPI_Documentation_online.pdf
• http://www.jennessent.com/arcview/TPI_Weiss_poster.htm

Texture Shading

• http://www.textureshading.com/Home.html
• http://www.shadedrelief.com/texture_shading/

Kennelly and Stewart's Skymodels

• http://www.mountaincartography.org/publications/papers/ica_cmc_sessions/8_Dresden_Session_Mountain_Carto/dresden_kennelly.pdf
• https://pennstate.pure.elsevier.com/en/publications/general-sky-models-for-illuminating-terrains

RCP repo (use this instead of the repo linked in the blog post below)

• https://github.com/jacobdadams/rcp

rcp installation guide and reference

• https://gisjake.blogspot.com/2018/10/introducing-rasterchunkprocessingpy-aka.html

conda.md

Setting up a GDAL conda environment

Create an environment

conda create -n <environment_name>

Activate the environment

activate <environment_name>

Install gdal from conda-forge

conda install gdal -c conda-forge

terrain_commands.md

Terrain commands

Adding Overviews

gdaladdo -ro in.tif 2 4 8 16

• -ro means open the tif in read only mode, which results in an external overview file in.tif.ovr, just like ArcGIS. Internal tif overviews are tricky, and I try to avoid them.
• The 2 4 8 16 are the pyramid levels. I find these four levels to be sufficient for most of my state-wide to local maps, but this depends on your extent and the resolution of your raster.

Basic Hillshade

gdaldem hillshade in.tif out.tif

Multi-directional Hillshade

gdaldem hillshade -multidirectional in.tif out.tif

Combined Hillshade

gdaldem hillshade -combined in.tif out.tif

Slope

gdaldem slope -p in.tif out.tif

• -p means return the value in percent slope instead of slope in degrees.

Topographic Position Index (TPI)

gdaldem TPI in.tif out.tif

Texture Shading

1. gdal_translate -of EHdr -ot Float32 in.tif temp.flt
   • Translates our input tif to a .flt
2. texture.exe <texture_level> temp.flt temp_texture
   • <texture_level> is a number between 0 and 2. Use 2 to get extreme edges like Tom Patterson uses for his canyon walls and alpine hatching.
3. texture.exe <vertical_enhancment> temp_texture final_texture.tif
   • <vertical_enhancement> is a number, usually between -2 and 5, that controls the contrast. Play around for artistic value.

Skymodel using rcp.py (github.com/jacobdadams/rcp)

1. Generate a luminance CSV from SkyLum.exe.
2. Delete the header rows so that the first row of the csv is the first row of values.
3. python path/to/rcp.py -s 800 -o 600 -p 6 -m skymodel -l path/to/luminance.csv in.tif out.tif
   • -s 800 uses 800 x 800 pixel chunks. Setting this higher results in exponentially slower runtimes.
   • -o 600 spececifies an overlap of 600 pixels on neighboring chunks (the skymodel algorithm shades out to a max of 600 pixels, so setting this lower than 600 will result in visible seams).
   • -p 6 processes six chunks in parallel. Set this based on the number of logical cores in your system; I recommend using n-1 or n-2 cores if you're going to be doing anything else while processing.
   • -m skymodel tells it to create a skymodel. rcp.py has several other tools, including and adjustable TPI algorithm and several smoothing algorithms.
   • -l luminance.csv is the path to the luminance csv generated and cleaned up earlier.
4. Wait. A state-wide-plus-50-miles, 10-meter-resolution file using 250 light points (specified in SkyLum.exe) took over three days running on 11 or 12 cores of an Intel i7-8700. The roughly 9600 x 6700 pixel tif in the livestream took 50 minutes with the same luminance csv.

Yeah, that is a result of the -o value not being 600. The overlap determines how far outside of the chunk it reads data from for algorithms that need to know what's happening beyond the chunk (like skymodelling).

I've not documented this very well on this page, but the shading algorithm for skymodelling looks 600 pixels away from each pixel to determine whether it would be shaded for a given sun altitude and azimuth. Therefore, the overlap value needs to be 600 so that the pixels near the edge get the full shading effect.

I've always used the -s 800 -o 600 settings for 10m x 10m DEMs. You can always try going into the code and changing the 600 pixel value (the max_steps variable at https://github.com/jacobdadams/rcp/blob/master/methods.py#L324) and see what it looks like with a smaller value. Essentially, this will decrease the maximum length shadows can be, but with a 25x25m DEM a smaller value could give the same effective shading as my 600 pixels at 10m.

As you've probably seen, an overlap this increases the runtime significantly. Someday I'll try to optimize this, but that's where we're at right now.