[GRASSLIST:430] Re: how to refer to cell's ,longitude latitude coordinates?

[Vishal Mehta]

thanks everyone,

i'll try r.sun, but i thought i'd like the freedom of running my own
algorithms- i'm not sure i'll have access to the papers that are referred to
in the r.sun help page, to check out the algorithm.

meanwhile, here is what i'd like to do, using either r.sun or my own
algorithms. If you can suggest some *general* steps, that would speed up my
attempts:

I want to create a monthly map of extraterrestrial radiation, and net
radiation, on a 0.5 degree grid for extents 60 -100.5E and 5 to 45.5N. I am
not particular about corrections for aspect and slope at this point. So
particular questions i have now are:
a) I already have a location with the above coordinates and cell size. Can i
use r.sun on an empty map or do i absolutely need an elevations, slope
and aspetc map?

b) At this point i can only derive monthly radiation maps by summing the
daily estimates in r.sun- right?

thanks all!
vishal


On 3/27/06, Glynn Clements <glynn at gclements.plus.com> wrote:
>
>
> Vishal Mehta wrote:
>
> > I have a raster map, lat/long, 0.5 degrees resolution. I want to develop
> > solar radiation and related maps maps using r.mapcalc. This requires
> > refering to each cell's latitude and longitude, i.e. the equations will
> > include the cell's latitude and longitude. How do i do this in GRASS? Is
> > there like an intenral variable that indexes each cell's coordinates?
>
> In r.mapcalc, the x() and y() functions return the coordinates of the
> centre of the current cell.
>
> --
> Glynn Clements <glynn at gclements.plus.com>
>
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