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I am kind of a beignner in ArcGIS and thought about and googled this problem for two days now.

I am working in ArcScene making a 3D visualization of a bedrock surface of a town. I have a polygon layer floating on the base heights of the dem (digital elevation model) for bedrock surface. I also have a raster layer (orthophoto) floating on the base heights of a dem for the ground surface in the area.

Here comes the tricky part for me: In some places, the bedrock surface is reaching above the ground surface. This means that the dem for the bedrock surface is not polated that well since it should only reach ground level (says my professor).

How can I fix this? Can I set that the dem for bedrock can not exceed the height for ground dem? Or can I change the maxmum height in some parts of the map in other ways? The two dems have the same coordinate system.

Crossing my fingers for help!

All the best

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  • See if my answer below helps. I am curious though, and I am not a geologist so I apologize if this is stupid, but wouldn't bedrock that pierces the ground's surface be an outcropping (hence making your bedrock DEM acceptable)?
    – Chaz
    Nov 24, 2015 at 14:50
  • @chaz. I think the OP means that the bedrock surface height is incorrect if it is over the DEM. Its an error in the bedrock data (or the DEM data!).
    – David W
    Nov 26, 2015 at 19:05
  • Celsuis, out of curiosity, do othophotos have vertical datums associated with them? If your bedrock is, say, at NAVD88 and your other raster is different, wouldn't that contribute to the bedrock poking through where it shouldn't?
    – ChrisB
    Jul 27, 2016 at 14:15
  • This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review
    – Dan C
    Jul 27, 2016 at 16:04

2 Answers 2

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Expression suggested by @Chaz will result in island like elevation model, because condition, where bedrock is below surface missing. The expression in field calculator should look something like:

Con ("bedrock">"dem", "dem","bedrock")

Depending on raster namings in the table of content.

The better tool for this job is cell statistics set to obtain minimum.

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  • Hey, great advices, it helped me to finally get a good result. I first used the tool Minus from Maths where I took the ground DEM minus the bedrock DEM. After that I used Con and took true raster for ground DEM and false raster for bedrock DEM when value>0. Problem solved! Thanks.
    – Celsuis
    Nov 25, 2015 at 21:07
  • Glad it works. Mark it as solved please
    – FelixIP
    Nov 25, 2015 at 21:45
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Depending on the version of ArcGIS Desktop you are running the steps for this may be different, but the concept remains the same. You want to use a conditional raster expression here that will:

  1. Query areas of the bedrock DEM that are greater than the ground surface DEM
  2. Set those areas equal to the ground surface DEM

Use the Con tool, or the Raster Calculator to accomplish this (both work the same way just have a different way of inputting information)

Con Documentation:

http://resources.arcgis.com/en/help/main/10.2/index.html#//009z00000005000000

Raster Calculator Documentation:

http://resources.arcgis.com/EN/HELP/MAIN/10.2/index.html#//009z000000z7000000

Example of how this might look in the raster calculator:

con((bedrock_dem > ground_surface_dem), ground_surface_dem, bedrock_dem)

Edit: As @FelixIP mentioned I should have added the bedrock DEM as the final argument to the expression. This will serve as the the "false" condition.

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  • 1
    Thank you! I will check this out as soon as I have access to GIS again tomorrow. About the question of the bedrock piercing the ground; Yes, it would be an outcrop! But the ground DEM should include all kind of topography/surfaces, so where there is an outcrop, the bedrock surface should be at the exact same level as the ground DEM. :)
    – Celsuis
    Nov 24, 2015 at 16:07
  • Haha of course (obviously)! Thank you. I must need another cup of coffee. Hope my solution helps.
    – Chaz
    Nov 24, 2015 at 17:04
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    Yes it helped, finally I got a result with help from the Minus tool and thereafter the Con tool. Problem solved!
    – Celsuis
    Nov 25, 2015 at 21:09

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