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Raster Calculator Merge Function in ArcGIS 10?

MichaelDulin

I'm trying to merge DEM grids using raster calculator.
Is there a command to merge rasters using raster calculator in ArcGIS 10? In 9.3 the command worked like this: Merge ([dem1], [dem2], [dem3])

That command doesn't seem to work since the switch to python script.....

Thanks for any advice.

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Robert_LeClair

Hello,

You could simply add the rasters together in the raster calculator. For example "InRaster1" + "InRaster2" + "InRaster3" and define the output as a new raster dataset.

Cheers,

Robert LeClair
Esri-Denver

JeffreySwain

Not necessarily. The add will only work if the spatial extent is set and there are values for the NoData areas. If there are not any values there, the Add will only return the intersection of the two rasters. You would have to make the spatial extents match and then change the nodata values to 0 rather than null and then when you add them, the raster would look appropriate.

I would recommend using the Mosaic to New Raster Tool in Data Management > Raster > Raster Dataset to complete the process since the 'merge' functionality is no longer available in Raster Calculator.

http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//001700000098000000.htm

2021-08-06_8-52-53.png

JamieKass

You could also do this:

Con(IsNull("raster1"),0,"raster1") + Con(IsNull("raster2"),0,"raster2")

It basically says "if a cell is null, make it 0, then add them".

EricRice

The old Merge command has nothing to do with arithmetic. It is (was) a mosaic operation.

-Eric

real size.png

WillBreitkreutz

Not necessarily. The add will only work if the spatial extent is set and there are values for the NoData areas. If there are not any values there, the Add will only return the intersection of the two rasters. You would have to make the spatial extents match and then change the nodata values to 0 rather than null and then when you add them, the raster would look appropriate.

I would recommend using the Mosaic to New Raster Tool in Data Management > Raster > Raster Dataset to complete the process since the 'merge' functionality is no longer available in Raster Calculator.

http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//001700000098000000.htm

This is absolutely ridiculous, taking away the flexibility and usability of raster calculator combined with the old arcInfo functions was one of the worst design flaws of Arc10...

SteveLynch

Why not use CellStatistics with the ignore_nodata
option.

Steve

curtvprice

This is absolutely ridiculous, taking away the flexibility and usability of raster calculator combined with the old arcInfo functions was one of the worst design flaws of Arc10...

Most of the Spatial Analyst tools are available in the new Raster Calculator. Mosaic and Mosaic To New Raster are not Spatial Analyst tools, so unfortunately they don't work in Raster Calculator.

I also miss the old Merge local function ("grab the first non-Nodata value in the list of rasters, cell by cell) and would like to see either its return or a method to replicate it using the current functions in 10.0. It was a nice simple operator that did a simple thing -- tools like that are handy in map algebra when you're trying to solve a complex problem! (Now that I think about it, adding a FIRST and LAST statistics to Cell Statistics would be an easy way to implement Merge without adding another function. Good idea for ideas.esri.com!)

JohnChurchill

I miss this function as well. While going through and updating old Python scripts I wrote for 9.3.1, I wondered what happened to this (which landed me here). I suppose I will have to use the Mosaic mentioned above instead. Bummer. I also miss having functionality right in the Spatial Analyst toolbar when working within ArcMap. Now I have to go into the toolbox just to use the raster calculator.

curtvprice

. I also miss having functionality right in the Spatial Analyst toolbar when working within ArcMap. Now I have to go into the toolbox just to use the raster calculator.

I certainly do not miss having four different map algebra environments, each with its own architecture and quirks:

Arc 9x Map Algebra Parser: Historical source
Raster Calculator: ArcGIS 8x / ArcView 3x "raster engine" (note, does not honor GP environment!)
Single-Output Map Algebra: ArcGIS 9x
Multi-Output Map Algebra: ArcInfo Workstation "grid engine" (only reads grids)
Tool interface: ArcToolbox

In 10.x only one Python Map Algebra syntax and toolset is used, regardless of interface (python, modelbuilder, tool, Raster Calculator Tool), and honors the same geoprocessing environment as all other non-Spatial Analyst ArcGIS tools. Not to mention it directly reads and writes non-grid raster formats!

I recommend trying the python command window with its intellisense if you do a lot of interactive raster processing. Change is a hassle, I agree, but I believe you'll eventually really like it.

I suppose I will have to use the Mosaic mentioned above instead

The Mosaic tool is tricky because you need to create an empty raster and mosaic into it. I highly recommend setting the bit depth explicitly to avoid issue with NoData. (I usually set it to 32-bit signed if the input is a grid, just to make sure the NoData stays that way.) Mosaic To New Raster is okay, but I've found the Mosaic tool slight more robust because of the bit depth issue.

As mentioned above, another possible replacement in your workflow (if you don't need Mosaic's nifty edge-merging in overlap areas) is the Cell Statistics tool, which does a cell by cell statistical merge and has the (neat) option to ignore NoData cells.

MichaelSchwartz

I have found that for rasters that are 1/0 or 1/NoData you can use Cell Statistics �?? Max and make sure the �??Ignore NoData�?� box is checked. Works like a charm!

IHS-New-Logo-2018-alt3.png

zhaojunwang

it works for me. Thanks

milansmart

Yeah, very simple and useful tool, I can't believe I didn't know it 😄 Thanks a lot!

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