Projecting raster Cell Size.

Question

I am trying to project SRTM dem raster into a projected co-ordinate system with tool Project Raster. I know SRTM 1 sec dem's cell size is 30m(approx) but when projecting to Albus Equal Area projection the cell size changes to 34m+ . While UTM projection shows 30m cell size. Should I put the cell size manually in Albus Equal Area Projection?

DanPatterson_Retired · Answer

For any tool in Arctoolbox, there is an Environments tab on the bottom of the tool dialog.  So in the Project raster tool (or any tool for that matter), I always click on the environments tab to ensure everything is as I want it to be.  Then there are no surprises, no assumptions made an no mistakes.  In your case, I would want to specify the cell size in the raster properties and any other raster parameters as you see fit.  Eventually this behaviour becomes second nature, and if things go wrong, you know you have to back and check your environment parameters

NazmulAhasan · Answer

Thank you for your response. As I now understated some pixel will be removed or added to compensate for cell size enlargement or reduction. But my question is what happens when I put cell size manually?. Is it ok to put cell size manually or when should I put it manually? Sorry for being such a noob.

DanPatterson_Retired · Answer

There are some good points made in the Project Raster—Help | ArcGIS Desktop tool discussion

and here How Project Raster works—Help | ArcGIS Desktop

The decision should be based on the measurement scale of the input data (in your case it is elevation which is 'interval data' if you consider that the reference point for elevation is arbitrary)

The projected cell will be square and because of the northward change in the longitude line (meridians) a cell in degrees is not going to translate directly to an absolute planar measure.

I would chose a desired cell size, an appropriate method ( ie nearest neighbor probably) and examine the results.  If you are concerned about the difference between 30 and 34 meters, do both, then subtract the results using the 30 meter projected raster as the basis for comparison.  You are not going to get a direct translation of the values in the original srtm because the projection process is going to add rows and columns to the projected output in any event.