Deleting portion of raster using ArcMap?

Question

How do I delete a portion of a raster image using ArcMap?

Attaching the raster image and the portion to delete.

Answer 1

The manipulation of raster in ArcMap unfortunately requires additionnal extension (to be bought in addition to ArcMap).

If you are "lucky", you have the ArcScan extension. Then go to the "Raster Cleanup" menu on the ArcScan toolbar > "Start Cleanup" > Raster Painting. Then use the "fill" tool and you are done in one more click.

If you have the more frequent "spatial analyst" extension (required for most raster processing tasks), it is still possible but longer. Draw a vector polygon manually around the portion that you want to delete, convert your feature class to raster, then use Map algebra tool to set a background value to all pixels under the shape of your vector polygon

Con(IsNull("your_polygon_converted_to_raster"), "your_other_raster", "your_background_value")

If your background value is "NoData", then you can simply omit the last part (or use Setnull)

Con(IsNull("your_polygon_converted_to_raster"), "your_other_raster")

Answer 2

You could do this in a couple lines of code with the "raster" package in R. There's a function that will do exactly what you want.

R has a learning curve, but it might be worth it. I personally find all of the tools, add-ons, and menus in ArcMap to be confusing and unwieldy.

To do this, first create a polygon in Arcmap that contains all of the pixels that you want to mask out. A rectangle will do - just make sure it roughly covers the island you're trying to remove, and none of the pixels that you want to keep.

library(raster)

r <- raster("path/to/your/raster")
s <- shapefile("polygon/to/mask.shp")

r <- mask(r,s)

writeRaster(r,"path/to/write/raster.tif", format="GTiff", overwrite=TRUE)

Answer 3

The issue here is that the pixels representing the island fall within the extent of the entire raster, so applying standard find and replace techniques won’t work as it would end up applying it to the entire raster. With this in mind this is how I would do it:

1. Zoom into the island, so only the island pixels are showing, so no mainland coastline
2. Run Create Constant raster setting cell values to 9999, ensure you set processing environment to current display and snap raster to 2000.tif. This will create a small raster of pixels all 9999 for the current extent so should cover only your island and surrounding nodata pixels. If you have pixels with 9999 as a value then choose some other number that is outside the existing range of cell values.
3. Run mosaic tool and mosaic the 9999 raster into your 2000.tiff. You now have a raster with an ugly rectangle of cells in the sea where the island was and all this within your original DEM.
4. Run the calculate statistics and build raster attribute table to update the raster.
5. Run Set Null tool, the expression would be "Value" = 9999, false raster would be input raster. This will replace the block of 9999 cells with no data and as they are the only cells that are 9999 then the rest of the raster remains the same. This will effective delete out the island.