Combine/Merge Multiple Rasters/DEM into Single One

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05-27-2013 10:00 AM
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New Contributor III
I need to combine/merge/mosaic 18 DEMs into one and then use it to generate slope data.

What are the proper steps?  I've tried 'Mosaic to New Raster' but it didn't work (gave me a single dark piece of junk!)

I'm attaching a few DEMs here.

P.S.  I generated the DEMs using contour/breaklines in ArcGIS.


Thanks!
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MVP Regular Contributor
Use 'Mosaic to New Raster'. Make sure Pixel Type is set to 32_BIT_FLOAT. If you get a 'dark piece of junk', don't worry, the data is correct, you just need to calculate statistics so ArcMap can stretch it for display.
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MVP Notable Contributor

Even though it's nearly five years old, this response was very helpful! 

I'm not sure why but setting the pixel type to 32_BIT_FLOAT totally fixed my issue!

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New Contributor

Yes I had the same great experience! Thanks a lot!

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Occasional Contributor
You're best off creating a mosaic dataset. For advantages of this over other formats refer to the arcgis online help.

In ArcCatalog create a new File Geodatabase.

Right click on new File Geodatabase then scroll to 'New' then select 'Mosaic Dataset'.

Give the Mosaic Dataset an appropriate name then press okay.

Now right click on new mosaic dataset in ArcCatalog and select 'Add Rasters'.

In the Add Rasters to Mosaic Dataset GUI in 'Input Data' select dataset then navaigate and select the rasters you want to create the Mosaic Dataset with.

In the advanced options section of the GUI tick 'Build Raster Pyramids', 'Calculate Statistics and 'Build Thumbnails'.

Click okay to add the rasters to the mosaic dataset.
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New Contributor III

Hi,

I have to merge many DTM into one and I have followed the steps above provided by Geospatial Technology.

I got the DTM merged but it is a big grey chunk and even if Ihave ticked the "Calculate statistics" box it doesn't change.

Any other suggestion on what can be done?

Many thanks,

F

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Regular Contributor III

Did you apply a stretch to it in the Layer Properties - Symbology tab?  You might try the Percent Clip, ESRI or Min-Max.  You might also use the Hillshade tool on it to see if you can generate a meaningful Hillshade, although that too might benefit from a stretch.

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