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I have a question regarding DEM. I have downloaded SRTM DEM 30 m and I did a mosaic for the data using Mosaic tools in Arcmap to a Mosaic to a new raster. However, I got a DEM raster with values of 0-255 . I need to have a DEM values with meters not with the values of 0-255. I did convert the raster to 32-float but I still get the same value 0-255. and the cell size is 0.0002777.

Any idea how to convert DEM raster with values of 0-255 to values represent elevations?

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    Not really sure why that is. Are the pre-mosaic rasters projected? Converting to 32-float after the mosaic has created 0-255 values probably won't help. Need to sort out the processing of the mosaic. Other options are mosaic datasets if you have a standard or advanced license. – DMusketeer Oct 15 '15 at 11:55
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    Are you positive that is a DEM, and not the hillshade of a DEM? – Barbarossa Oct 15 '15 at 12:57
  • I agree with @Barbarossa, it sounds like you have downloaded an image of the SRTM data and not the data itself. I would go back to the site you downloaded it and check what you downloaded. I've used the USGS EarthExplorer website in the past to get SRTM data. – Hornbydd Oct 15 '15 at 13:40
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When creating the mosaic, make sure you select the same pixel type as what your input DEMs are using - for instance "8_BIT_SIGNED", and not "8_BIT_UNSIGNED". "8_BIT_UNSIGNED" would give you a 0-255 value. ESRI help on the topic is available here.

  • DEMs are far more likely to be 16_BIT_SIGNED or 32_BIT_FLOAT, though I suppose an extremely low-lying region could have an 8-bit DEM (e.g., Florida in meters, though not feet). – Vince Oct 15 '15 at 15:29
  • Sure, though the 0-255 values are only available for 8_bit_unsigned in the create mosaic tool, so I reckoned this is what what used here. – Hélène Oct 16 '15 at 7:56

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