Performing if else condition on two raster layers

[LawrenceSekaluvu]

Hi,

I am working on a project and i am writing my scripts in python. However, i am experiencing an obstacle that might make me quit this project for good. Here is is the problem. I want to perform a if else condition on two raster layers that have constant values across all there grid. Initially, i create two raster layers, each with a constant value within each cell. However, when i perform a loop on these two raster layers, one of them at the end will have cells with different values and i need to loop in again to compare it with the other raster with a constant value. I tried using the "Con" tool but things have not worked at all.  Any clues please?

[IanMurray]

Could you be a little more concise in explaining what you are trying to do? 

[DanPatterson_Retired]

Definitely include what you have tried either within the Con statement or within your script

[LawrenceSekaluvu]

@Dan,

I did that but when I use the Con statement, there is one moment when i have to compare a raster layer with all cells having the same value against a constant value, and In this case i get an error  message. However, if i perform the same Con condition on a raster layer with a range of cell values and specify the condition within the value range, it works out quite well with out bring any errors. May be there is some else hidden that i don't understand!!

[DanPatterson_Retired]

I would still like to see the Con statements you used AND the error message, which is probably the key.

[LawrenceSekaluvu]

Here is the error message i get

""

ERROR 999999: Error executing function.

The table was not found. [VAT_Con_plus_ras1]

A column was specified that does not exist.

A column was specified that does not exist.

The table was not found. [VAT_Con_plus_ras1]

The operation was attempted on an empty geometry.

ERROR 010416: Error in setting raster table filter for D:\Codetrial\Cond.gdb\plus_ras2.

ERROR 010213: Error in reading raster M0.

ERROR 010325: Run-time error - ***.

ERROR 010067: Error in executing grid expression.

Failed to execute (Con).

   """

[DanPatterson_Retired]

hmmmm quick guess...it is a floating point raster, hence it has no table, hence no field named value so you can't query a value field

[DarrenWiens2]

Just checked it out, Dan. I get Lawrence's exact error message by leaving the variable name inside the where clause:

>>> val = 580
>>> C = arcpy.sa.Con("block_dem_1m.tif","block_dem_1m.tif","","VALUE > val")

... but not like so:

>>> C = arcpy.sa.Con("block_dem_1m.tif","block_dem_1m.tif","","VALUE > " + str(val))

The above is a floating raster, with no table.

[DanPatterson_Retired]

Rules that out then...thanks for the update and you appear to be correct about the " locations

[LawrenceSekaluvu]

@Darren, i have tried out that and it works well with a raster having a range of values a cross the grid cells. However, it doesn't work out for rasters with a constant value across the cells.