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Author Topic: Problems with DEM in ArcGis  (Read 11931 times)

Kjellis85

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Problems with DEM in ArcGis
« on: October 06, 2011, 12:27:42 PM »
Hi

I am trying to import a DEM of a 3D model into ArcMap 10, but every time I try it seems that the DEM has wrong spatial information compared to the geographical one, even though I set it to be the same in photoscan as in arcmap. Anyone have any idea what could be wrong?

Alexey Pasumansky

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Re: Problems with DEM in ArcGis
« Reply #1 on: October 06, 2011, 02:56:59 PM »
Hello Kjellis,

Can you open the same DEM in the ArcGIG Explorer and if so does if appear in the proper area?
Have you experienced similar problems with previous version of PhotoScan?
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Alexey Pasumansky,
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Kjellis85

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Re: Problems with DEM in ArcGis
« Reply #2 on: October 06, 2011, 03:57:32 PM »
I tried opening the DEM (and a geo/tif) in arcgis explorer, but both ended up being placed in the middle of africa, not north of norway as they should. Am I doing something wrong when I am georeferencing? It seems as if there is something wrong with the coordinates, even though I use the same coordinate system.

I added a pic of what the layer properties look like, the extent looks really weird.

Alexey Pasumansky

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Re: Problems with DEM in ArcGis
« Reply #3 on: October 06, 2011, 04:12:13 PM »
Hello Kjellis,

Could you please provide a screenshot of PhotoScan Ground Contol dialog box with coordinates of markers/cameras and selected geographic coordinate system?
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Alexey Pasumansky,
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Kjellis85

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Re: Problems with DEM in ArcGis
« Reply #4 on: October 06, 2011, 04:20:32 PM »
It looks like it should, but i'm getting less wise by the minute. The bad thing is that I don't have any other examples to test this on at the moment.

Alexey Pasumansky

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Re: Problems with DEM in ArcGis
« Reply #5 on: October 06, 2011, 04:50:12 PM »
Hello Kjellis,

We have checked the coordinates with on-line converter and they seem to be in Africa. Please check you have the correct coordinates. For Norway you should have y-coord be greater by order than x-coord and here you've got inverse situation.
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Kjellis85

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Re: Problems with DEM in ArcGis
« Reply #6 on: October 06, 2011, 06:03:33 PM »
Hmm. seems like I might have some problems with my gcp's. I switched x and y, but they are still off. Going to do some more tests tomorrow, hopefully it will sort itself out.

Kjellis85

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Re: Problems with DEM in ArcGis
« Reply #7 on: October 12, 2011, 01:43:37 PM »
So, I have been playing around with the data and found the problem; the gcp file had somehow the wrong coordinates. But even after fixing the problem, the raster data will not place itself in the correct position. I get a message from arcmap that the datum is not the same, even though i have selected the same datum as my shapefiles. Have tried loading the file in arcexplorer as well but it places the raster about 3km south of the intended position. Don't know whether it is caused by the transformation or if it is due to the data.

I added the gcp file, it is correct (x and y may be switched, but otherwise working).

EDIT: I got it working, although I am not quite sure how. It seems as if there was something happening when I exported the file in wgs 1984 33N, so I tried exporting it in just wgs 1984 and it worked.
« Last Edit: October 12, 2011, 02:35:26 PM by Kjellis85 »

Kjellis85

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Re: Problems with DEM in ArcGis
« Reply #8 on: October 12, 2011, 03:14:23 PM »
Turns out I have another problem with the DEM; it shows one value that is -32 767 meters, while all others are correct. Is this a bug or is it a known problem?

Alexey Pasumansky

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Re: Problems with DEM in ArcGis
« Reply #9 on: October 13, 2011, 03:36:28 PM »
Hello Kjellis,

Quote
Turns out I have another problem with the DEM; it shows one value that is -32 767 meters, while all others are correct.
It might be the format incompatibility problem. Could you please answer what format are you using for this DEM?
Best regards,
Alexey Pasumansky,
Agisoft LLC

Kjellis85

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Re: Problems with DEM in ArcGis
« Reply #10 on: October 13, 2011, 03:45:18 PM »
GeoTIFF. It seems as if the parts that are outside of the model is given this very low value, while the rest is fine.

Alexey Pasumansky

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Re: Problems with DEM in ArcGis
« Reply #11 on: October 13, 2011, 04:02:53 PM »
Hello Kjellis,

Undefined regions outside the model are saved with large negative values outside of the data range of the valid regions. Normally GIS software should detect this and correctly handle such undefined regions. Does ArcGIS behave differently? Do you have a sample GeoTIFF DEM with partial coverage that is handled properly by ArcGIS so that we can compare the data?
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Alexey Pasumansky,
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Kjellis85

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Re: Problems with DEM in ArcGis
« Reply #12 on: October 14, 2011, 06:17:19 PM »
I solved the problem, it turned out to be a function in arcgis which had to be turned on. Thanks for the help

tdepke

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Re: Problems with DEM in ArcGis
« Reply #13 on: November 13, 2011, 10:21:37 AM »
Hello there Kjellis,

Can you share what function in ArcGIS you had to turn on to get whatever you did to work? I am using my own Cartesian coordinate system and I am also ending up with HUGE negative values, which seem to be where the model ends and where there are holes. I am trying to use this DEM with another DEM exported through PS to do a DEM subtraction to estimate volume change. Do you know how I could do that without including these large negative values in Arc?

Thanks,

Tyler