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I have eight DEM tiles that I downloaded from the USGS National Elevation Dataset. The individual rasters are displaying correctly, but when I try to combine them in a Raster Mosaic I get arbitrary values (3.4+038 -> -3.4+038), which is considered to be NoData.

I've tried several times, half the time I get a warning message upon creation of the Mosaic (001003: Datum Conflict) even though I was sure to match coordinate systems. I've even imported the coordinate system from one of the rasters going into the mosaic.

The mosaic shows the footprint of the DEM, but none of the data Mosaic

I had a similar problem here, but I followed the process of converting to tif before I tried to mosaic the images.

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2 Answers

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Calulate statistics on the raster.

You need the statistics to be able to apply stretches etc when displaying your new mosaic. The values you see are just the default max and min values possible for the pixel depth of your raster and not the actual range of the data within it. You will get the proper range once you compute statistcs.

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It seems like that should be a default setting or at the very minimum not tucked away in the Add Rasters... option on the Mosaic Dataset. – Roy Jun 27 '12 at 16:07
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...or better still an automatic process on creation of the raster... but then ESRI is quirky :) – MappaGnosis Jun 27 '12 at 16:13
I jumped the gun there -- the Mosaic is still displaying those odd values even after calculating stats for all rasters and the raster mosaic. – Roy Jun 27 '12 at 16:28
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It could well be due to another ESRI quirk. This is, when ever you open a raster, ESRI will create RRD and AUX files. These are the pyramids and a pointer to the pyramid. It then uses these files to enable rapid display of the raster. BUT they sometimes persist even after computing statistics and similar operations meaning you are effectively displaying the wrong data even though you have updated it. Shut your MXD and hill both the RRD and AUX files for your mosaic. Then open it again (the RRD and AUX will be recreated - or you can tell ESRI to compute the pyramids manually). – MappaGnosis Jun 27 '12 at 16:52
up vote 4 down vote

I ran into the same issue today, the following worked for me:

  1. Create raster mosaic dataset. Make sure to specify your pixel type. In my case, I specified 16 bit unsigned.
  2. In the "Add Raster to mosaic dataset" window check the "update overviews" box. Under "Advanced Options"
  3. Also from the advanced options, import your coordinate system. Make sure to select "Calculate Statistics" , "Build Raster Pyramids" and "Build Thumbnails"
  4. Finally, run a sample on 4 images, rather than your entire dataset, to make sure you get the results you want.

Good luck!

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