How to use SRTM DEM files for shaded relief in ArcMap?

Question

I would like to create a nice shaded relief for France using SRTM3 data. Most of the threads on the subject are from awhile ago, when ArcMap was not able to import these without changing the file extension.

Now, it seems, ArcMap can import the .hgt files just fine. The problem is that the value for elevation is set at 32767 to - 32767. If I change the symbology settings and set the stretch value to standard deviation. This sets the values much lower and you can see the elevation differences.

A complete set of images is present at this imgur album showing the comparison, stretch setting, and final difference.

This creates two more problems: - How might I do this on a mass scale? I've searched for tools and unfortunately most conversion custom toolkits seem to be inaccessible. - Each hgt file seems to be shaded differently, due to the changing of the stretch value to standard deviation, as seen below:

I apologize if this is something that has been covered before. I am still relatively new to the world of Cartography and GIS so there may be a simple tool that I should be using.

Many thanks for any guidance on the subject.

Answer 1

You often see this type of behavior with strange min/max values in ArcGIS when a raster does not have statistics calculated or is in certain formats. It is more of a display issue than data integrity. I would convert your raster from its current format to a native ESRI grid format or img. You can do this by right clicking on the raster in ArcCatalog and selecting Export > Raster to Different Format... You can also right click on a raster and select calculate statistics... Working with rasters in other formats can yield unpredictable results.

To fix the differences along tiles just mosaic the source DEM's together before calculating a shaded relief. The correct tool for this is Arctoolbox > Data Management Tools > Raster > Raster Dataset > Mosaic to New Raster

Answer 2

Each Image will be stretched according to it's histogram. This is why, if you have individual tiles, it is very difficult to get their renderers matched exactly.

What is usually done in this case, is that all the tiles are Mosaiced to a new Raster, and you render the new complete Raster according to your needs.

If the data is good, (I have never had a problem with edgematching SRTM data) you get a seamless mosaic where you cannot see any boundaries, and the whole raster is rendered with one stretched renderer.