topic $$NCOLS + $$ROWMAP in ArcGIS Spatial Analyst Questions

$$NCOLS + $$ROWMAP

YongTian — Sat, 21 Jan 2012 01:44:39 GMT

How do we implement $$NCOLS + $$ROWMAP in map calculator? I would appreciate any advice. My email: yong.q.tian@gmail.com

Re: $$NCOLS + $$ROWMAP

ChrisSnyder — Tue, 24 Jan 2012 16:56:21 GMT

Unsuported in new v10.0 Map Algebra! Although you can get $$NCOLS through the describe property in Python or the GetRasterProperties toolbox tool.

See: https://c.na1.visual.force.com/apex/ideaView?id=087300000008DT2AAM#comments

You can still use the good ole' Map Algebra sytax in v10 though:

arcpy.gp.SingleOutputMapAlgebra_sa(blah, blah)

$$NCOLS + $$ROWMAP

CameronScott — Wed, 10 Apr 2013 15:15:53 GMT

Thanks for this! I'm new to both rasters and Python so code like this is a HUGE help. However, I think there's a small bug.

Shouldn't the xmap setting be adding XMin instead of YMin at the end? I.e.,
xmap = (FlowAccumulation(tmpg) + 0.5) * cellSize + E.extent.XMin

Thanks again for the code, very useful.

$$NCOLS + $$ROWMAP in ArcGIS 10 Python map algebra

curtvprice — Sat, 11 Dec 2021 13:17:48 GMT

Here's an implementation of William Huber's neat idea of using the FlowAccumulation tool to generate xmap and ymap. This uses the current processing environment, it will generate an error if the arcpy.env.extent or cellSize are not explicitly set.

(this code has a bug fixed - thanks Cameron!

from arcpy.sa import *
from arcpy import env as E
# Calculate $$NROWS and $$NCOLS from current environment
cellSize = float(E.cellSize)
nrows = int((E.extent.YMax - E.extent.YMin) / float(E.cellSize))
ncols = int((E.extent.XMax - E.extent.XMin)  / float(E.cellSize))
# Bill Huber's method for $$XMAP and $$YMAP: "1" flows "right", "64" (63+1) flows "up"
tmpg = CreateConstantRaster(1)
xmap = (FlowAccumulation(tmpg) + 0.5) * cellSize + E.extent.XMin
ymap = (FlowAccumulation(tmpg + 63) + 0.5) * cellSize + E.extent.YMin
# applying the same method for $$ROWMAP and $$COLMAP
colmap = Int(FlowAccumulation(tmpg))
rowmap = Int(FlowAccumulation(tmpg + 3))  # flowdir "4" is "down" (top row is 0)

Re: $$NCOLS + $$ROWMAP in ArcGIS 10 Python map algebra

XanderBakker — Sat, 29 Nov 2014 17:55:41 GMT

It's always cool to see some of William Huber‌ ideas revive!

Thanx for sharing Curtis Price‌

Re: $$NCOLS + $$ROWMAP

curtvprice — Tue, 02 Dec 2014 04:13:09 GMT

No problem, I was just resurrecting some old posts of mine, getting them tagged and placed in GeoNet where they will be easier to find.