How to: Set raster values to NoData easily in ArcGIS 10
While processing some data at work today I had an issue where I had a raster dataset in ArcGIS, where all cells with invalid data had been set to 9999. Of course, this caused a lot of issues for the statistics on the dataset – basically they were all nonsense – so I needed to fix it. I couldn’t seem to get reclass to work properly with floating point data, so I posted a question to the GIS StackExchange site. Within a few minutes I had a couple of answers: one suggesting a possible way using the interface, and one suggesting a method using the ArcPy API.
However, I managed to find a way to do this easily using the approach recommended for ArcPy in the response from Aragon (thanks!), but using the GUI interface. To do this, follow the instructions below:
1. Run the Spatial Analyst -> Conditional -> Set Null tool
2. Set the input conditional raster to be the raster dataset which you want to change
3. Set the expression to VALUE = 9999 where 9999 is the value that you want to replace with NoData.
4. Set the Input false raster or constant value to the same raster dataset that you select in step 2.
5. Choose a sensible output raster. The dialog should look roughly like this (click for more detail):
6. Click OK
It’s done! Your new raster should have all of the values of 9999 replaced with NoData, and your statistics should work fine.