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caltopo DEM Shading

Posted: Wed Oct 02, 2019 6:16 pm
by SSSdave
At this time of year I'm increasingly on ski boards and decreasingly on hiking and backpacking boards. On a thread about slope steepness, someone pointed to a caltopo feature, Digital Elevation Model (DEM) Shading. I then played around with it to figure out the syntax and found I could program the Rules section to create shading with different colors. Of course one can just look at the closeness of vertical elevation lines, however the color shading does enhance understanding in numerical terms what one is looking at and presents a new way to look at terrain. Note there is a default DEM shading option but it uses a limited subset of degrees and does so over whatever colored base map is used that results in varying colors. The below long string is just one link to a view of the Crystal Range Cathedral Peak zone. One can use the link to move around to other locations without having to set up the below modes and options I've included below for the sake of documenting what is done. ... 2%7D%5D%7D

Under topographic maps select Forest Service 2013 as it is the only topo type map with contour lines that has a white background. Otherwise whatever colors are selected for DEM shading will be a less obvious transparent blend of whatever else is below on the map. At the Additional Layers Custom Layers section, select DEM. Note the FS 2013 maps only include National forest areas. If not in NF, also in Map Overlays, select Contours and MapBuilder Overlay. At the Terrain Modeling section select the pencil icon that pops up the Digital Elevation Model Shading window. In the Rules section paste in the below:

s00-05 17E517
s05-10 7EE517
s10-15 E5E517
s15-20 E57E17
s20-25 E51717
s25-30 E5177E
s30-35 E517E5
S35-40 7E17E5
S40-60 1717E5

That is the correct syntax as lower case won't work and the slope numbers need to have 2 digits. The actual assigned color does not show but rather a less saturated variation in order to be transparent. I used the Photoshop Color Picker window to select the colors by setting Saturation to 90, Brightness to 90 and Hue starting at 90 degrees for the lowest gradient and subtracting 30 degrees on the color spectrum for each 5 degrees of slope change. Then copied the hex color values that resulted. Thus:

s00-05 (120 degrees cyan green)
s05-10 (90 degrees green)
s10-15 (60 degrees yellow)
s15-20 (30 degrees orange)
s20-25 (0 degrees red)
s25-30 (330 degrees crimson)
s30-35 (300 degrees magenta)
S35-40 (270 degrees purple)
S40-60 (240 degrees blue)

5 degrees = 8.75% grade
10 17.63
15 26.79
20 36.40
25 46.63
30 57.73
35 70.02
40 83.91
45 100.00
50 119.17

In order to understand other map features, switch between Forest Service 2013 and Hybrid or Scanned 7.5m.

Re: caltopo DEM Shading

Posted: Wed Oct 02, 2019 8:43 pm
by c9h13no3
The main thing I use slope angle shading for is:
a) to figure out if I'm in avalanche terrain when snow's not consolidated.
b) to determine if I need to bring the ice axe & crampons in the summer.