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Re: map_set stereographic projection [message #48588 is a reply to message #48520]

Fri, 28 April 2006 10:24

James Kuyper
Messages: 425
Registered: March 2000

Senior Member

mattie wrote:
> kuyper@wizard.net writes:
>
>> dvila wrote:
...
>> ; These are the u-v values corresponding to pixel centers along each
>> edge.
>> topv = (uv[1,1]+uv[1,2])*0.5
>> botv = (uv[1,0]+uv[1,3])*0.5
>> leftu = (uv[0,0]+uv[0,1])*0.5
>> rightu = (uv[0,2]+uv[0,3])*0.5
>
>
> Aren't these the u-v values corresponding to the _center_ of the
> gridcell along each edge? (assuming the initial data gave the
> centerpoints of the gridcell.)

Yes, that's what my comment line says.

...
>> ; U-V coordinates of midpoints of outer edges
>> u = [leftu-0.5*xscale, 0.5*(leftu+rightu), rightu+0.5*xscale, $
>> 0.5*(leftu+rightu)]
>> v = [0.5*(botv+topv), topv+0.5*yscale, 0.5*(botv+topv),
>> botv-0.5*yscale]
>> lonlat = MAP_PROJ_INVERSE(u, v, MAP_STRUCTURE=stereo)
>> limit = [lonlat[1,*],lonlat[0,*]]
>
> Again, I'm not sure, but don't you have to add half a gridcell to each
> direction to get the outter limit of each grid cell?

Yes, that is precisely why I wrote such things as "leftu-0.5*xscale",
etc.

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[Message index]

		map_set stereographic projection By: dvila on Thu, 27 April 2006 05:50
		Re: map_set stereographic projection By: dvila on Mon, 01 May 2006 08:12
		Re: map_set stereographic projection By: James Kuyper on Fri, 28 April 2006 21:18
		Re: map_set stereographic projection By: David Fanning on Fri, 28 April 2006 16:06
		Re: map_set stereographic projection By: James Kuyper on Fri, 28 April 2006 15:59
		Re: map_set stereographic projection By: David Fanning on Fri, 28 April 2006 12:52
		Re: map_set stereographic projection By: mattie on Fri, 28 April 2006 12:41
		Re: map_set stereographic projection By: James Kuyper on Fri, 28 April 2006 10:24

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