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I downloaded ASTER GDEM Tiles and mosacked them in ENVI. After that I exported the Mosaic in tiff format and I opening it in Arcgis, the image is gray all through but the pixels are showing correctly. I want to run some algorithms like slope, contour and Hillshade.

What should I do to get the algorithms?

  • I don't mean to be a fly in the ointment but Esri hillshade isn't the best. If you have GDAL (QGIS, OSGeo...) GDAL_DEM (arguably) does a better job. Hillshade is a visual product so one will say 'Product X' is better, the other will say 'Product X' is worse. Try both, see which one you like, and it will do slope as well - not that there's much difference between Esri and GDAL with respect to slope/aspect. – Michael Stimson Mar 25 '15 at 3:34
  • @MichaelMiles-Stimson Does that include the new multi-directional hillshade? Ama - do you have Spatial Analyst? That has tools in the Surface toolset that do all three things you're looking at. (Note that hillshade is different than the one I asked Michael, and is probably the one he is referring to.) – Chris W Mar 25 '15 at 5:40
  • @Chris-I have it, the problem is the image is all gray. But in envi the image openned okay. During Mosaicking in envi, I saw all the features of the image but I could not get all the necessary tools to person what i want. – Ama Mar 25 '15 at 7:18
  • @Ama use envi to get slope and hillshade with envi (hillshade is better in envi) – Pau Mar 25 '15 at 11:49
  • Okay, Thank you, its always nice to share a problem with intellectuals. I discovered that my NoDATa values were not set and after doing that in ERDAS imagine, the exported tif worked well in Arcgic but my resolution was 150x150 and I am going to scale up to 30x30. – Ama Mar 26 '15 at 7:19
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It sounds to be like you have not assigned the nodata values correctly. To correct this, try:

Spatial Analyst Tools -> Conditional -> SetNull.

Select your raster as the input conditional raster AND the input false raster and type in the “Expression” box: Value < -10 AND Value > 9000 (case and space sensitive).

This means: “Set to Null all the points that fulfill the statement and use the value from the input false raster every time the statement is not verified”. Give a name to the output raster and click OK.

This should solve your problems.

  • That's not the right tool.. maybe. Set Raster Properties will affect the dataset as it stands without creating a new one. I would say the user should build statistics - ENVI wouldn't have done that, if it did it would be in a way that Esri isn't reading. – Michael Stimson Mar 25 '15 at 3:28
  • Oh yes, in ERDAS I would set all nodata to 0 and compute statistics while ignoring 0. – Corse Mar 25 '15 at 3:29
  • It depends if all of the input tiles have the same NoData. If some are -99999, others have -99 and a few with 0 then yes Con, Extract by Attributes or SetNull is the way to go. If you can pick the NoData value from the raster then it's quicker to set it... note, this can also be done in ArcCatalog by right clicking on the raster, select properties, find NoData value and hit 'set' button. In the end though NoData has to be a single value. – Michael Stimson Mar 25 '15 at 3:38
  • The image displays a high value of 32767 and low value -32767. It openned quite okay during mosaicking in envi but it cannot open in arcgis in in tif format. When I tried processing slope with it the a notice displayed" one or more dropped items were invalid and will not be added to the control" – Ama Mar 25 '15 at 7:25
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    @Ama try compute histogram of the image, i think that it´s the automatic display of envi is better than the one of arcgis – Pau Mar 25 '15 at 11:56

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