Removing a polygon-defined area from a multiband raster: A landscape classification inquiry

Question

I am trying to exclude multiple lakes and reservoirs from a Supervised landscape classification but at the moment I have not found a way to do this. So far I have used the following workflows:
1.Draw a polygon -> Clip -> Extract by mask) generates the opposite result.
2.Draw a polygon -> "Raster to Polygon" -> Reclassify -> Set Null, but the reclassification removes RGB symbology
Details:
I am using an Multiband High resolution Raster image
I am working on the latest version of ARCmap for Desktop
I would like to retain the RGB Composite symbology

Hornbydd · Answer

The erase affect you are seeking can be achieved with a simple workflow, captured as a model. Inputs are a raster and a polygon featureclass. In my example a single polygon has been selected.

The model is:

Logic is:

You convert your polygon to a raster dataset with the same cell size of your raster you want to erase from and make sure snap raster environment setting is set. Also ensure processing extent is set to your raster. The result of this will create a new raster the same extent, cell size and alignment as your raster.
Reclassify the rasterized polygon into a 1 for polygon an 0 for nodata to make a raster where all cells are either 1 or 0.
Use the SetNull tool to set the polygon (cells with values of 1) to NODATA and cells with 0 to the raster. The set null tool is set up as:

The result is a raster where the polygon was is now NODATA.

Removing a polygon-defined area from a multiband raster: A landscape classification inquiry

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