topic Re: Arc10 workaround to $$XMAP and $$YMAP in Data Management Questions

Generate a grid of latitude values

ToddMcDonnell — Fri, 30 Apr 2010 14:18:12 GMT

I need to convert a 30m elevation grid to a grid that gives values for the cell latitude rather than elevation.

I tried converting the GRID to point, adding x,y data to the points, then converting back to GRID using the y-coordinate as the value, however, the large region I am working with is preventing the processes from completing successfully.

Any advice will certainly be appreciated.

Todd

Re: Generate a grid of latitude values

SeanMcLaughlin — Fri, 30 Apr 2010 15:18:39 GMT

What is the area, or how large of an area is it?

Re: Generate a grid of latitude values

LukePinner — Mon, 03 May 2010 02:05:49 GMT

Is the grid in a geographic coordinate system?

If so, just set your output extent and cell size (ArcToolbox environment settings or Spatial Analyst toolbar options) to match your DEM then use $$YMAP built in scalar variable in a SOMA/MOMA tool or Raster Calculator expression:

E.g.
C:\workspace\latgrid = $$YMAP

Luke

PS: For info...

Built-in GRID scalar variables:
$$NROWS: the number of rows in the analysis window
$$NCOLS: the number of columns in the analysis window
$$CELLSIZE: the current cell size specified in the analysis environment
$$WX0: minimum x-map coordinate of the current analysis window
$$WY0: minimum y-map coordinate of the current analysis window
$$WX1: maximum x-map coordinate of the current analysis window
$$WY1: maximum y-map coordinate of the current analysis window
$$XMAP: x-map coordinate for the center of the processing cell
$$YMAP: y-map coordinate for the center of the processing cell

Built-in GRID constants.
PI: 3.142
E: 2.718 (e)
DEG: 57.296 (Degree to radian conversion)
GAMMA: 0.577
PHI: 1.618

Built-in grids.
$$ROWMAP
$$COLMAP

Re: Generate a grid of latitude values

DanielLusher — Fri, 06 Aug 2010 11:15:27 GMT

Luke (or anyone else who can help),

I've read your post on this thread, and your thread on the old forums (http://forums.esri.com/Thread.asp?c=93&f=1740&t=182407&mc=6#msgid538607), but I'm struggling to get the $$xmap scalar variable to work with the SOMA tool. It works in the Raster Calculator, but since I am trying to create a model, I need to use the SOMA tool. At the moment, I am trying

$$xmap = (D:\...\Base Data\dem3_4m)

in the "Map Algebra expression" box, and have tried variations including switching the order of variables, spaces and no spaces, no equal sign, etc. I still get an error saying that "$$xmap = is not a valid function or operator." I also cannot find where it would be in the "Usage" listing.

I am currently running ArcView 9.3.1 SP 2 with the Spatial Analyst extension, on Windows 7.

Thank you for any ideas you might have!

Re: Generate a grid of latitude values

DanielLusher — Mon, 09 Aug 2010 12:43:44 GMT

Figured it out - needed to set the extent, snap raster, and cell size in the "Model Properties" to make it run. Put "$$xmap" in the "Map Algebra expression" text box and it ran fine.

Re: Generate a grid of latitude values

JenifaLatha — Tue, 30 Nov 2010 05:27:15 GMT

Dear Sir
I need to create a lattitude grid from the DEM. I have gone through the threads and followed the steps. When I type the statement $$YMAP in SOMA window after setting the extent, working directory and cell size by the spatial analyst > options, i get an error message that "Syntax error at locations 0 of expressions $$YMAP". I even changed the expression as E:\Ph.D\Data_dump\DEM = $$YMAP. How to access these built in functions? Kindly help me sir.
With Thanks

Re: Generate a grid of latitude values

EmmanuelJjunju — Tue, 18 Jan 2011 17:19:51 GMT

I have tried this is arcGIS10 raster calculator and it doesn't work!! Any new detailed instructions on how to generate the grid of latitudes?

See screen capture attached please.

Re: Generate a grid of latitude values

toddsams — Tue, 18 Jan 2011 20:15:12 GMT

I have not tried the raster calculator method.

However, I have had luck using the function "genvecgrid" in the Geospatial Modeling Environment (GME). After generating the vector point grid I added x-y coordinates to the attribute table. Then, created a raster from these points using the y-coordinate field as values. I think I chose a bilinear interpolation technique when doing this.

Re: Generate a grid of latitude values

GJtB — Tue, 25 Jan 2011 12:20:47 GMT

Hi,
I have the same Problem as ejjunju ($$XMAP or $$xmap doesn't work in ArcGIS 10)

I want to create rasters with x-Values and do not have a clue how to Do it with the raster calculatur. I could create point-features, use "Add XY" and then convert it to rasters, but as I have to automatize it it seems to be too complicated.

I also have problems finding documentation/ tutorials on Map Algebra syntax. Does anyone know some sources for this

Greetings
Gerald

Re: Generate a grid of latitude values

MannyGimond — Wed, 02 Feb 2011 11:46:42 GMT

Hi,
I have the same Problem as ejjunju ($$XMAP or $$xmap doesn't work in ArcGIS 10)

Unfortunately, ESRI removed those grid functions from 10.0. However, there is a Python alternative, see this link .

Re: Generate a grid of latitude values

GJtB — Wed, 02 Feb 2011 12:05:36 GMT

Hmm,
Thanks.

Looks like I have to get a little more familiar with Python then.
😕

Does anyone know Tutorials that make it easier to start with ArcPy?

Greetings
Gerald

Re: Generate a grid of latitude values

MannyGimond — Wed, 02 Feb 2011 12:14:05 GMT

Hmm,
Does anyone know Tutorials that make it easier to start with ArcPy?

For starters, you might want to read "An Introduction to Python and the ArcPy site-package" in the latest issue of ArcUser.

Also, if you want to cast a vote for the reintroduction of the grid functions, go to this link.

Re: Arc10 workaround to $$XMAP and $$YMAP

MannyGimond — Thu, 03 Feb 2011 14:36:33 GMT

There are several workarounds that use only map algebra.

As a worked example let the origin be at (-500000, 0) and the cellsize be 10. Then[INDENT]xmap = (FlowAccumulation(1) + 0.5)*10 - 500000
ymap = (FlowAccumulation(64) + 0.5)*10
[/INDENT].

Very clever Bill. This deserves its own sticky (if stickies are implemented on this forum).

arcpy map algebra $$ROWMAP, $$COLMAP

curtvprice — Tue, 24 Jan 2012 22:16:11 GMT

Bill, thank you very much for this!

I worked out a more detailed implementation of your idea here:
$$NCOLS + $$ROWMAP in ArcGIS 10 Python map algebra‌

Re: Arc10 workaround to $$XMAP and $$YMAP

RakhshanRoohi — Sun, 12 May 2013 21:32:35 GMT

Bill, thank you very much for this!

I worked out a more detailed implementation of your idea here:
[post]166151[/post]

Hi,
I tried to open this link but it did not work. could you please elaborate this. I am struggling to solve this issue as well. Your help will
be highly appreciated.

Cheers

Re: Arc10 workaround to $$XMAP and $$YMAP

curtvprice — Mon, 13 May 2013 00:06:54 GMT

I fixed the link above.

Don't like it that the post number changed -- I thought those were permanent links!

Re: Generate a grid of latitude values

FrankHanssen — Mon, 16 Jun 2014 07:43:58 GMT

Taking out the $$YMAP and $$XMAP was really a big mistake!!!! Why spend a lot of energy on python scripting instead of using these excellent and easy to use commands??? Please put them back!

Re: Arc10 workaround to $$XMAP and $$YMAP

FrankHanssen — Mon, 16 Jun 2014 09:55:42 GMT

Oops... there's a typo, and now it got quoted! The correct formula in the example is
[INDENT]xmap = (FlowAccumulation(1) + 0.5)*10 + 500000
[/INDENT](because one subtracts the coordinates of the origin instead of adding them).

Bill, I am stucked here and anoid that $$XMAP and $$YMAP are removed from 10.1.

I have tried to implement your tip in my raster calculator whitout success. What is wrong? I would like to avoid Python...

xmap = (FlowAccumulation(1) + 0.5)*10 + 500000
ymap = (FlowAccumulation(64) + 0.5)*10

Re: Generate a grid of latitude values

curtvprice — Fri, 25 Jul 2014 20:56:47 GMT

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

Re: Generate a grid of latitude values

LuizVianna — Sat, 11 Dec 2021 20:52:26 GMT

This worked for me, for southern hemisphere (negative lat and lon). It is necessary to set the environmental options before running the script.

import numpy as np
import arcpy
from arcpy.sa import *  
from arcpy import env as E

#Create variables from environment
latmin = E.extent.YMin
latmax = E.extent.YMax
lonmin = E.extent.XMin
lonmax = E.extent.XMax
cellsize = float(E.cellSize)
lowerleft = arcpy.Point(lonmin, latmin)

#Generating inverse meshgrid for latitude grid
lat1 = np.arange(float(-latmax), float(-latmin), float(cellsize))
lon1 = np.arange(float(-lonmax), float(-lonmin), float(cellsize))
lon1, lat1 = np.meshgrid(lon1, lat1)

lat = arcpy.NumPyArrayToRaster(-lat1, lowerleft, float(cellsize), float(cellsize))

#Generating meshgrid for longitude grid
lat2 = np.arange(float(latmin), float(latmax), float(cellsize))
lon2 = np.arange(float(lonmin), float(lonmax), float(cellsize))
lon2, lat2 = np.meshgrid(lon2, lat2)

lon = arcpy.NumPyArrayToRaster(lon2, lowerleft, float(cellsize), float(cellsize))‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍