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I'm getting funky results from Extract By Mask (spatial analyst). I'm clipping a Raster Mosaic of DEMs from the National Elevation Dataset with polygons. I have a script to run through 15 separate polygons, however, after getting strange results I've resorted to trying to get a single mask to run.

I'm getting a warning that there is a Datum conflict, but I was careful to make sure to use the same Datum...

My inputs: Inputs

My output: Outputs

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Have you tried clipping the mosaics instead? (Data Management Tools > Raster > Raster Processing > Clip) –  veedub Aug 16 '12 at 13:50
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2 Answers

I got exactly the same type of striped output raster as you Roy when trying to export from a Mosaic Dataset with a modified boundary.

Notice that the right part of the image has proper results. The mosaic was build from two other Mosaic Datasets (690 and 530 tiles of 1m DEM) and the proper part is from the 530 tile part mosaic.

Both source Mosaic Dataset and the derived mosaic have the same default properties. I don't get it.

Edit: I figured out a workaround. Instead of using Copy Raster tool, as the ESRI manual says, I did a data export on the mosaic layer in Tabel of Contents.

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Just to clarify -- you're using 2 DEM tiles? I was using quite a few, which led me to believe it may be a memory issue. That's not something I'd expect with 2 tiles tho. –  Roy Oct 9 '12 at 11:15
    
No that's not it. It was 2 Mosaic Datasets consisting of 630 and 530 tiles combined into one Mosaic Dataset. –  Mort Oct 9 '12 at 11:22
    
That could be the issue that's a heck of a lot of data. –  Roy Oct 9 '12 at 11:24
    
It is but the masked boundary covered only something like 40 tiles. Mosaic to New raster would probably handle it with ease if add those tiles individually. Maybe it's like you say a memory issue of the Copy Raster tool. –  Mort Oct 9 '12 at 11:41
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For whatever reason the large Raster Mosaic was giving me these strange results. I resorted to creating several smaller raster mosaics, which seemed to do the trick. The raster mosaic containing 4 NED tiles clipped as expected.

Maybe it's a memory issue?

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