[gradsusr] Hillshade

[Davide Sacchetti]

actually I perform something similar to hillshade, a kind of poor man
illuminated orography. It's a bit heavvy and complicated, anyway:

get the slope (orography derivative)
ex: slopex=cdiff(oro,x); slopey=cdiff(oro,y)

choose your light direction ...
ex.: slope=0.9*slopex + 0.2*slopey

define your greyscale palette and display slope

... see att.

Bye Davide





On Thu, 2018-02-15 at 14:17 +0000, Jennifer M Adams wrote:
> I had to google it — 'hillshade’ is a handy GIS function for making
> topography look cool in a 2D plot. Best I can offer is the formula
> used for the topographic background maps in the forecast maps at
> wxmaps.org. Start with a high-res topo data, e.g.:
> 
> ga-> sdfopen http://monsoondata.org:9090/dods/topo/rose/etopo05
> ga-> z = maskout(rose,rose)
> ga-> div = hdivg(z,const(z,0))
> 
> —Jennifer
> 
> > On Feb 8, 2018, at 12:38 PM, Thomas Davies <tsd.davies at gmail.com>
> > wrote:
> > 
> > Hi,
> > 
> > I was wondering if there is an easy way to plot a map of global /
> > europe hillshade (not elevation) in GrADS? Do you know where I can
> > download such data that can be used with GrADS?
> > 
> > Thanks in advance
> > _______________________________________________
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> --
> Jennifer Miletta Adams
> Center for Ocean-Land-Atmosphere Studies (COLA)
> George Mason University
> 
> 
> 
> 
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