Re: Limb Darkening

Hi Martin,

while playing with solar eclipse paths I found NREL's SPA algorithm  
which gives Sun position and other values. Then you can to use Sun's  
elevation to know day/night.

http://www.nrel.gov/midc/sampa/

Eduardo.-

Quoting Martin Connors <[email protected]>:

> Hi all,
>  looks like we are heading to a nice 2014 with GMT 5 out and good   
> discussions. A few months ago I was trying to do "scientific   
> illustration" with an Earth with night and daysides, so sort of what  
>  is asked for here. See my script fragment below and note some   
> symbols are undefined in this fragment, but I think you can figure   
> them out.
>
>  In attachment is the code for illumination. As noted in Eduardo   
> Suarez' posting, it is hard to find a "nice decay rate". For   
> testing, my code can be uncommented to have a rather sharp day/night  
>  boundary. The illumination is then overlaid with transparency, and   
> to see it you have to make a PDF file.
>
> Enjoy...Martin
>
> paltb=gray
> makecpt -C$paltb -T0/1/0.01 > illum.cpt
>
> # center of projection
> lonp=280.34
> lonp=320
> latp=75
>
> projection="JG$lonp/$latp/$D1"
> region="Rg"
>
> ./illumination $geonoon | surface -Rg -I1/0.1 -T0 -Gillum.grd
>
> pscoast -$region -Dc -A10000 -$projection -B30g30/15g15 -W1 -X$xoff   
> -Y$yoff -Sblue -Ggreen $orient -K > illum.ps
>
> # grdimage with transparency -t% from 0 (opaque) to 100 (transparent)
> trans=10
> grdimage illum.grd -$region -Cillum.cpt -$projection -K -O -t$trans   
> >> illum.ps
>
> ps2pdf illum.ps
>
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-- 
Eduardo A. Suarez
Facultad de Ciencias Astronómicas y Geofísicas - UNLP
FCAG: (0221)-4236593 int. 172/Cel: (0221)-15-4557542/Casa: (0221)-4526589


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