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Question

Terrain analysis: Slope and total height

J

I'm trying to analyse an area/DEM with these two criteria:

 

-Even sloping terrain steeper than 1:20 and total slope height > 5 m.

Finding areas with slope of 1:20 (5%) could be done with the slope function. But I can't figure out an easy way to filter these areas to only include areas with slope height over 5 meter. I.e. the total vertical height form start of slope to top should be at least 5 meters.

Anyone have any ideas or thoughts on this problem?

 

 

Background: The criteria are to identity possible land slide areas (quick clay), so it's already clipped to only include areas of old marine sediments. https://www.ngu.no/en/topic/quick-clay-and-quick-clay-landslides

3 replies

nathanatsafe
Safer
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Hi @jespergrandin, thanks for your question!

 

If I understand correctly, you're looking to output a raster that highlights pixels with a slope greater than 5% AND an elevation greater than 5 m. This can be done by creating two separate rasters - one holding the elevation data, the other holding the slope data. Then combine the two rasters into one raster with two bands using the RasterBandCombiner. Finally, a conditional statement with your two conditions can be constructed in the RasterExpressionEvaluator to output a single band raster with your desired pixels.

 

 

I've constructed a sample workspace using Vancouver DEM data to get you started (see below). You should find all the steps there, although you'll need to tweak the parameters to fit your data.

 

rastercon.fmwt

 

 

Hope this helps!

 

Nathan
J
nathanatsafe wrote:

Hi @jespergrandin, thanks for your question!

 

If I understand correctly, you're looking to output a raster that highlights pixels with a slope greater than 5% AND an elevation greater than 5 m. This can be done by creating two separate rasters - one holding the elevation data, the other holding the slope data. Then combine the two rasters into one raster with two bands using the RasterBandCombiner. Finally, a conditional statement with your two conditions can be constructed in the RasterExpressionEvaluator to output a single band raster with your desired pixels.

 

 

I've constructed a sample workspace using Vancouver DEM data to get you started (see below). You should find all the steps there, although you'll need to tweak the parameters to fit your data.

 

rastercon.fmwt

 

 

Hope this helps!

 

Nathan
Hi @NathanAtSafe, thanks helping out!

 

I have updated the question, since I need the total height of an entire slope, say, a hill face.

 

Disclaimer - I have not viewed your model yet since I'm not at work.

 

S
  • sblazey
  • September 4, 2020

Hi @jespergrandin​ , I realise this question was posted nearly 3 years ago, but I am curious to know if you figured out a way to do this. We are trying to do something similar: we want to find areas with slope of at least 3:1 (33% grade) where the total distance from start of slope to top is at least 10m.

Thanks!

Stephanie

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