Generate a coordinate (latitude) image?

Jonathan Greenberg <greenberg <at> ucdavis.edu> writes:

Folks:

Is there any way to take a raster and generate two outputs where
each pixel is the center coordinate of that pixel (e.g. you will have
one x- image and one y-image)?  I'm trying to produce a "latitude map"
for solar calculations.

--j

You could use coordinates(as(obj, "SpatialPixels")) but only for relatively
small rasters. And why not calculate by hand?

On Tue, May 17, 2011 at 7:25 PM, Jonathan Greenberg

Folks:

Is there any way to take a raster and generate two outputs where
each pixel is the center coordinate of that pixel (e.g. you will have
one x- image and one y-image)? ?I'm trying to produce a "latitude map"
for solar calculations.

--j

If you are using the spgrass6 library you should be able to use the
y() argument in the r.mapcalc command from GRASS. I say should because
I have only done this in GRASS directly not using spgrass6.

Hope this helps,
Michael

--
Jonathan A. Greenberg, PhD
Assistant Project Scientist
Center for Spatial Technologies and Remote Sensing (CSTARS)
Department of Land, Air and Water Resources
University of California, Davis
One Shields Avenue
Davis, CA 95616
Phone: 415-763-5476
AIM: jgrn307, MSN: jgrn307 at hotmail.com, Gchat: jgrn307

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36.214177, -81.681480 +/- 3103 meters

Folks:

Is there any way to take a raster and generate two outputs where
each pixel is the center coordinate of that pixel (e.g. you will have
one x- image and one y-image)?  I'm trying to produce a "latitude map"
for solar calculations.

   

If you mean "each pixel value  is the center coordinate of that pixel" 
you could proceed like this:

# (first, I built a raster for my toy example)
library(maptools)
data(meuse.grid) # only the non-missing valued cells
coordinates(meuse.grid) = c("x", "y") # promote to SpatialPointsDataFrame
gridded(meuse.grid) <- TRUE # promote to SpatialPixelsDataFrame

# now, assign the coordinates as values to each pixel
meuse.grid[["xcoord"]] = coordinates(meuse.grid)[,"x"]
meuse.grid[["ycoord"]] = coordinates(meuse.grid)[,"y"]

image(meuse.grid["xcoord"]) # note the single [
image(meuse.grid["ycoord"])

Cheers,
  Marcelino

--j


   

_________________________________ Marcelino de la Cruz Rot Departamento 
de Biologia Vegetal E.U.T.I. Agricola Universidad Politecnica de Madrid 
28040 Madrid Tel: 34913365654 _________________________________

Folks: 

Is there any way to take a raster and generate two outputs where 
each pixel is the center coordinate of that pixel (e.g. you will have 
one x- image and one y-image)?  I'm trying to produce a "latitude map" 
for solar calculations. 

--j 

Jonathan, 

If your data are in lon/lat

r <- raster()
x <- init(r, v='x')
y <- init(r, v='y')


Or "by hand", for lon/lat do

lat <- yFromRow(r, 1:nrow(r))

if the raster is not lon/lat

xy <- SpatialPoints(xyFromCell(r, cellFromRowCol(1:nrow(r), 1)))
lat <- coordinates( spTransform(xy, CRS( +proj=longlat +datum=WGS84 )))[,2] 

In cases like this, I stop here. Rather than making a latitude raster with
lots of repeated values, I would work with the lat vector. But you could do
something like this:

x <- t((t(r) * lat))
plot(x)


Best, Robert
 

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