[GIS] Con expression in two rasters ArcGIS, raster calculator

arcgis-desktopconraster-calculatorspatial-analyst

I would like to write a condition in ArcGIS 10.1 in Raster calculator.

I have 2 overlapping rasters (Ras1.img, Ras2.img) with different attributes in attribute table:

Ras1.img: Class – results of supervised maximum likelihood classification
Ras2.img: Att – landuse, raster converted from shapefile polygon format

I want to change pixel values Class in Ras1.img based on the values in Att, Ras2.img. something like:

if ((Ras1.img, Class == 20 & Ras2.img, Att == 5), then change Class value 20 in Ras1.img  to Class 25))

I can't figure that out. It is super simple in R, but I have no idea how to make it in ArcGIS 10.1.

I was trying to figure that out by : http://resources.arcgis.com/en/help/main/10.1/index.html#//009z000000zn000000

and applying something like:

Con(("landuse1" == 1) & ("landuse2" == 5), "landuse1" + "landuse2", 99)

but I don't understand where I specify the attributes of my rasters I would like to change?

Best Answer

Try the Reclassify tool: http://desktop.arcgis.com/en/arcmap/10.3/tools/spatial-analyst-toolbox/reclassify.htm

Open this tool and you should be able to input your raster, then redefine pixel value(s).

Related Solutions

[GIS] Replacing Raster Values in Ras1 with Ras2

Do you have access to spatial analyst? If so, the Con function will do exactly what you want. Create a "condition" raster that is 1 where you want the values changed to Ras2 and 0 everywhere else. Execute the statements:

Ras1 = Con(Raster("condition"), Raster("Ras2"), Raster("Ras1"))
Ras1.save("Ras1")

This will replace Ras1 with your new raster. If you just want to create a new raster, change the string in the save function. If you do not have access to spatial analyst, I will see if there is a way around using the Con function.

ArcGIS 9.3.1 Raster Calculator method:

Again, assuming you have a condition raster as above.

outraster = con(condition > 0, Ras2, Ras1)

In the raster calculator, you just use the direct references rather than using the Raster function as I did for arcpy. You would then need to save your outraster and replace Ras1 with it.

[GIS] Remove (or SetNull) areas of overlapping rasters using ArcGIS Desktop

First, you should make sure your roads and hydrology feature classes are being rasterized appropriately. You should make sure that the cell size and snap raster (i.e. pixel registration) matches your suitability layer. If you don't, the rasterized roads and hydrology could have much larger cells than intended or be misaligned, leading to undesirable results. Set the snap raster and cell size environment variables in Feature to Raster, as shown below.

setting environment variables

Second is the part you were asking about: setting cells in suitability layers as null where the rasterized road (red) and hydrology (blue) layers have non-null values, as shown below.

input data

The easiest way to accomplish this is using Raster Calculator. The Map Algebra expression we want to use is SetNull(~IsNull("hydro.tif")|~IsNull("roads.tif"),"suitability"). Let's break this down step by step.

The SetNull tool requires two raster layers in the simplest usage. The first is a conditional raster, where cells not equal to zero (equivalent to boolean TRUE) should be set null. The second is the false raster, representing the desired output cell values where the conditional raster is equal to zero (equivalent to boolean FALSE).
We want the conditional raster (parameter 1) to be TRUE if either the roads or hydrology have non-null values and FALSE everywhere else. The OR operation is handled by a | (a vertical bar or pipe, the key right below backspace). To find non-null values, we can take the inverse (or boolean NOT) of the null values, which are found using the IsNull tool. To do the boolean NOT in raster calculator we use a tilde ~. Combining it all: ~IsNull("hydro.tif")|~IsNull("roads.tif").
We want the false raster to be our suitability layer, which you can pass in as-is.

final parameters

Here's the output, with the hydro and roads rasters correctly set null:

output

Best Answer

Related Solutions

[GIS] Replacing Raster Values in Ras1 with Ras2

[GIS] Remove (or SetNull) areas of overlapping rasters using ArcGIS Desktop

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