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Recently I got the SRTM DEM from Cgiar,which based on WGS84/EGM96.

and I merged the tiles to one tiff file. I want to get the WGS84 ellipsoidal heights.

According the steps from the Arcgis Help 10.2 "Converting from orthometric to ellipsoidal heights",I do the whole steps,but I found the tif file was not changed,the height was the orthometric height based on EGM96 geoid. I Want one tif format DEM with ellipsoidal heights based on WGS84 ellipsoid.

I don't know where the problem is?

The steps I followed :

Create a file geodatabase

Steps:

  1. Click the Catalog button on the Standard toolbar. This opens the Catalog window. In the Location text box, type C:\arcgis\ArcTutor\Raster and press ENTER.
  2. Right-click the Raster folder and click New > Folder. Name the folder Exercises.
  3. Right-click the Exercises folder and click New > File Geodatabase. Rename the new file geodatabase ImageGDB.

Set the default geodatabase

Right-click the ImageGDB geodatabase in the Catalog window and click Make Default Geodatabase.

Create a new mosaic dataset

Steps:

  1. Right-click ImageGDB in the Catalog window and click New > Mosaic Dataset. Type HMA in the Mosaic Dataset Name text box.
  2. Click the Coordinate System browse button . Expand Projected Coordinate Systems >, choose wgs84 world mercator.prj, then click OK. Click OK on the Create Mosaic Dataset tool dialog box.

Add rasters to the mosaic dataset

Steps:

  1. Right-click the SRTM mosaic dataset in the Catalog window and click Add Rasters. This opens the Add Rasters To Mosaic Dataset tool.In the Raster Type list, choose Raster Dataset.
  2. Click the drop-down arrow and click Workspace.
  3. Click the Input browse button. Navigate to C:\arcgis\ArcTutor\Raster\Data\SRTM_tif and click Add.
  4. Check Update Overviews.
  5. Click OK to run the tool.

Add the Arithmetic function

Steps:

  1. Open the Catalog Window and navigate to the mosaic dataset. Right-click the mosaic dataset and click Properties.Click the Functions tab.
  2. Right-click the Mosaic Function and click Insert > Arithmetic Function.

Input Raster 1 is identified as the current contents of the mosaic dataset and will not be changed. Click the Input Raster 2 browse button and navigate to the \pedata\geoid folder in the ArcGIS install location.Choose the WGS84.img and click Add.

  1. Click the Operation drop-down arrow and click Plus.
  2. Click OK to close the Raster Functions Properties dialog box.
  3. Click OK to close the Mosaic Dataset Properties dialog box.
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    Would you be able to update your question to explain some of the things you tried so far? I think it would help others find where the problem is. – SaultDon Oct 23 '14 at 1:52
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Based on the steps you tried so far I think you have only created an on-the-fly version of what you want. Mosaic datasets do not change or create any new rasters, they just process them on the fly for fast visualization. If you export the resulting mosaic dataset as a new raster you should get the result you want.

  • Thanks jmpreiks, I export the resulting mosaic dataset as a new raster using "Mosaic to New Raster",but it seems without height information. – Geodetic Oct 23 '14 at 21:32
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Download EMG96 data which is height of Geoid above the WGS84 ellipsoid. Then use raster calculator to add EMG96 raster to your CIGAR DEM. (You may need upsampling EMG96 raster to get the same resolution as CIGAR DEM)

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