Sinkholes from contours

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11-05-2013 11:16 AM
GrljAles
Occasional Contributor
Hi

For my diploma I'm trying to compare differnt methods of sinkholes extraction. For this purpose I would like to automaticly extract sinkholes from contours shapefile. While I succesfuly extracted the lowest contour of the sinkhole I have no idea how to select/extract the second, third... if a sinkhole has it.
Any suggestion will be more than welcome. Although I came across an article I do not fully understand the method used so I'm also posting a link to that article if anyone has time to check it and possibly exsplain something to me.

http://geomorphometry.org/system/fil...orphometry.pdf

Thank you very much.

Ales
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8 Replies
DaleHoneycutt
Regular Contributor
The link seems to be busted.
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KeaganAllan
New Contributor III
Hi,

Unfortunately the link is broken, so I cannot see how this has been done.
I can however, based on what you have said and my understanding of it, point out how things could be done.

The following is how I identify Ponding / Water Storage Areas - possibly you could modify this to fit your needs.

1) Take a contour dataset and convert this to  a TIN and then to raster (This raster dataset is your untouched original)

2) Can be done in two ways (a or b)

a) Take the original raster from 1 and perform a "Surface Fill" (located in the Spatial Analyst - Hydrolocial Tools), These may be tweaking required to get a decent result, but basically this tool fills all the holes or depressions in the raster surface to create a hydrological surface that allows for water to pass freely over it. Effectively this should "fill in" the sinkholes in the contour dataset.

b) Is similar to a, except you use the topo to raster interpolation in 3D or Spatial Analyst. One of the parameters in this interpolation is the number of iterations the interpolation is allowed to run, the more the process runs, the more smooth the surface will become. Effectively the result is similar to a.

3) After you have run a or b you can use the raster calculator to subtract the original raster (1) by the modified raster (2a or b), the result will be a raster with values from 0 to -xxx. Where 0 are areas where there was not alteration to the raster from filling in depressions and the -xxx are areas where the were depressions filled.

4) Running the contour tool on this raster will give you the contours of the sink holes. From the 0 contour down to the deepest - If you want it the other way around simply subtract Raster 1 from Raster 2a or b.

I am not sure if I have helped you or missed the point completely, but hopefully once the correct link is put up I can see what you needed.

Good luck, I look forward to reading the article.

K
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JasonScheirer
Regular Contributor II
Original link to paper is here. Must have gotten messed up in pasting from Map Automation forum to here.
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GrljAles
Occasional Contributor
Hi,

Sorry for late response.

Yes that's the article I was talking about, thank you.
Keagan Allan: Thank you for your response but I have alredy done that. I want to extract sinkholes directly from contours (without interpolating) to compare the results and consequently update the sinkholes extracted the way you described.
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KeaganAllan
New Contributor III
Hi,

Sorry for late response.

Yes that's the article I was talking about, thank you.
Keagan Allan: Thank you for your response but I have alredy done that. I want to extract sinkholes directly from contours (without interpolating) to compare the results and consequently update the sinkholes extracted the way you described.


Hi,

I will look over that article and see if I can decipher what was being done.
If you do come right please post the solution, I would love to know how to do this too.

Regards,

K
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GrljAles
Occasional Contributor
Thank you!

Just to clarify things a litle more:

I have two methods to work with on two datasets. The first is DEM in 5 m resolution on which I used the method described by Allan. I used "Fill" tool ten times each time with one meter larger Z limit, starting from one meter and finishing with ten. Then I converted each layer obtaned to Polygons and merged the results.
Other dataset is layer of contours from 1:25000 topographic map. As jou can see from the image (in attachment) the "Fill" tool did not capture all the depressions that can be seen on the contour map or some sinkholes were extracted poorly and I would like to update depressions from DEM with those from contours.
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KeaganAllan
New Contributor III
Hi thanks for clarifying that.

One thing I can think of is that some of those sinks that are not picked up may be smaller than 1m.
If you run the Fill Tool with no Z-Limits, are these smaller sinks identified?
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GrljAles
Occasional Contributor
Hi,

Just tried that but the results are almost the same though the tool picked some sinkholes that are deeper than 10 m and I wasn't aware of them till now.

However I think it could be possible to do this somehow with exporting all closed contours as separate polygon shapefiles and then using the "Select layer by location" tool and relationship "CONTAINS" or "COMPLETELY_CONTAINS". But then I would have to apply the condition that selects only contours (polygons) that have higher elevation value than the selecting feature.
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