Raster calculator expression & empty output grid problem

Question

Original User: valtersanches Hi All How do i should write the notation in raster calculator (using ArcGIS 9x) to calculate Flow Lenght (downstream): I tried this but something is wrong: FlowLength([flowdir_fill5],downstream). The command line syntax is: FlowLength_sa {DOWNSTREAM | UPSTREAM} {in_weight_raster}. If i use the notation: FlowLength([flowdir_fill5]), the output is a flow lenght upstream grid (I need the downstream). Before, i tried to use the Arctoolbox interface, but i have something wrong with my ArcGIS (9.3), because the output grid file is empty (see attached file), but, if i use the raster calculator, the output it's good (i did a test to slope raster with raster calculator and the output is good). Regards. FlowLenght.jpg Arctoolboox.jpg

valteralbino · Answer

Thank you Duncan, my syntax was not complete.
Now, the output grid files area fine.
But still, if i try through the GUI (Arctoolbox) gives an empty grid file...

Anonymous User · Answer

Original User: Hornbydd

OK a couple of other things to check:

Your flow direction grid, is it valid and for the area? When I say valid it has only the values of 1,2,4,8,16,32,64 & 128?

Do you have a pre-existing Processing Extent set which may be for some other region? You access that via the spatial analyst toolbar > options.

Finally if you are using the raster calculator from the spatial analyst toolbar have you tried the expressions

FLD = FlowLength([flowdir_fill5],"#","DOWNSTREAM")
FLU = FlowLength([flowdir_fill5],"#","UPSTREAM")

The expression for a raster calculator is flow direction grid, weight grid, keyword. So the "#" just means default as this is an optional parameter.

Duncan

valteralbino · Answer

Well,

I was trying to do with the raster calculator.
Also tried the example (without sucess):
flowlength([direction])
flowlength([direction], downstream).

The syntax FlowLength([flowdir_fill5]) gave the upstream output; but i'm still have problems in having the correct downstream output grid file.
I tried through the command line (but like the Arcoolbox GUI, it gave an empty grid file (see attached file).

Untitled-1.jpg