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#1
Matthew Hampton

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While exploring new techniques of elevation depiction, I developed something that worked and wanted to share. I did all of the work in ArcGIS, but it would be just as easy in QGIS.

First I used Spatial Analyst to create both a Slope surface and an Aspect surface, then converted the rasters to points and joined them together into a single file. After isolating all the points with aspects that should be shaded (SouthEastern aspects) I applied a b/w gradient based on slope values such that steeper slopes are depicted with darker values.

I've attached a standard analytic hillshade (albeit with a focal mean to smooth the detail) and a Dotshaded version below. I was curious if any others had stumbled upon this as well?
Attached File  HillShading.png   270.61KB   2 downloads Attached File  DotShading.png   84.82KB   4 downloads

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#2
hasecbinusr

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That's an interesting way of displaying relief. How did you find ArcMap handled the point files? In the past, when I've converted DEMs from raster to vector, the resulting files are far too large to process or display. Case in point, a raster of my last DEM was about 120 MB, but the point file was over 2 GB. Have you found an ideal data size for this process?



#3
Matthew Hampton

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The area that I am working on is only about 36 sq. mi and I am using a 30 ft grid, so viewing all 544,673 points takes a little draw time.  The point shapefile (14Mb) is significantly larger than the (tif) raster is was derived from (2.6Mb), but there could be some other advantages to using dot-shading over the traditional method.

 

Below is a set for a zoomed in area.  

 

Attached File  HS_Zoom.png   113.87KB   2 downloads      Attached File  PS_Zoom2.png   102.64KB   1 downloads


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#4
hasecbinusr

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Looking at it again, I wonder how it would look slightly modifying dot diameter based on relative elevation. Dots at the lowest elevation would be slightly larger, while dots at the highest elevation are slightly smaller. That coupled with your aspect shading might look really unique.



#5
tangnar123

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Cool method, thanks for sharing it. I like how this creates a crisp, but still generalized, representation of elevation.

 

It seems like you could thin the dots to optimize the file size while retaining the desired shading effect.  Also, if you were using this method on a web map, you could modify the number of dots that are drawn at different scales as necessary. 



#6
tangnar123

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I gave this a try yesterday using an area about 3 sq mi and 10ft DEM.  One difference that gave an interesting result is this:  

I selected the points from the entire southeast quadrant (90 to 180 degrees). I kept the aspect points and slope points separate, and styled each of them differently.  For the slope, I styled as suggested with steeper slopes darker.  For aspect, I styled the points to get lighter as they move away from 145 degrees in both directions.  This turned out to give a kind of nice effect of different degrees of shading. I put the slope on top of the aspect points and played with the opacity. 

 

I think I could resample the DEM to generalize some more, or possibly just clean up some of the lonesome points and unnecessary areas.  It's not as clean as the example you gave, but I think it looks interesting. 

 

Attached File  snip1.PNG   804.9KB   4 downloads Attached File  snip3.PNG   343.59KB   2 downloads






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