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I was wondering if anyone has had any experience with combining multiple DEM’s into a mosaic dataset. I am working with several DEM’s and need to convert them to slope. I’m having an issue with doing this w/ a mosaic vs. individually and can’t seem to locate any information to help me online. The output I get running them individually comes out correct, but is incorrect when run using the mosaic (see attached image, left is correct, right incorrect - obviously) Does anyone know if you cannot apply the slope tool or any other tool to a mosaic dataset? I would think no since this is such powerful software, so I’m assuming I’m doing something wrong. Any knowledge anyone has would be greatly appreciated.

P.S. I am using ArcInfo

slope screenshots mosaicslope rastertomosaic

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Example does not tell where is the difference. What exactly is incorrect? Is it float/integer data type related, extent, cell size etc.? – Tomek Mar 15 '12 at 10:53
it's not an extent problem. I made the image on the right semi-transparent so you can see the terrain underneath. It's not an extent issue even though the images show 2 different extents. The cell sizes are the same as well. Here is another shot of the right image w/o the transparency. It's assigning one value to the whole mosaic image. – niklas24 Mar 15 '12 at 11:23
Try creating new Mosaic Dataset, set Pixel Type 16_BIT_SIGNED (this should cover all elevations). Then again Add Rasters with Calculate Statistics advanced option checked. Check in ArcMap if you have correct elevations. – Marcin Mar 15 '12 at 11:33
thanks Marcin...I will try that and let you know if that works. – niklas24 Mar 15 '12 at 11:39
should update overviews be off? I had it on before. what about update cell size ranges, update boundary, those were defaulted on, but grayed out when I checked the update overviews box. – niklas24 Mar 15 '12 at 11:57

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