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Combine on two rasters with different cell size

DitlevReventlow

Hey everyone.

I have used the tool combine on two datasets that did not have the same spatial resolution. I can see that "Combine" has chosen the bigger cell size as the output raster spatial resolution.

How has combine calculated the output raster value for the raster that had the small cell size? I cant see anything about it in the combine tool help.

Thank you very much.

Best regards

Ditlev Reventlow

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IanMurray

Hi Ditlev,

I'm not sure which resampling method it would use(I would assume Nearest Neighbor, but ArcGIS has several other resampling options, including Majority, Bilinear and Cubic, and as you said there is no tool documentation for which is being used). If you want to guarantee which method is being used, I would recommend Resampling the smaller resolution raster first to the size of the larger resolution with the resampling method of your choice, then combining your rasters.

ArcGIS Help 10.1

DitlevReventlow

Thank you for this Ian, The problem is that I have already done the analysis, so I have to write the consequences and implications of this. I guess though that a solution could be to try the different resampling methods on the finer raster and see if one of them gives the same result as combine.

DitlevReventlow

Nope, this doesn't work, because although the cell size is the same, the position of the cell in the "new resampled file" and the combined file is different. Therefore, it will not be the same smaller cells that the two coarser raster datasets are derived from. Hope there is another solution to solving this problem.

SteveLynch

read up - processing extent and snap raster

DanPatterson_Retired

Follow Steve Lynch's advise and when you are using tools in ArcToolbox, there is the oft-ignored Environments button in the lower right of the dialog. That is where you should set all your raster parameters prior to running any tool. Do not assume that once you have set something ... OR ... you have set some of them somewhere else, that they will be retained and/or used. The rule is...if it isn't set, then a default will be used and a default is only as good as your data are perfect. You need to specify the extent, cell size and snap raster to align the cell edges...explicitly.

DanPatterson_Retired

it probably does truncation rather than rounding since the output of combine has to be an integer AND sequential...rounding could skip classes

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