[gradsusr] Topography data and hill shading

[Andrew Friedman]

Hi Howard,
Below are 2 recent suggestions from the listserve:
-Andrew

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http://gradsusr.org/pipermail/gradsusr/2018-February/041529.html
Davide Sacchetti, Thu Feb 15 10:07:53 EST 2018

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

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http://gradsusr.org/pipermail/gradsusr/2018-February/041527.html
Jennifer M Adams, Thu Feb 15 09:17:14 EST 2018
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
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> On Jun 13, 2018, at 8:56 PM, Howard Staines <rossby at rossby.co.nz> wrote:
> 
> Good morning,
> 
> I was looking for some relatively high resolution topography data ,,,
> covering NZ. I used to use some on monsoon . but that's no longer available.
> 
> Secondly I was wanting to do some hill-shading and was wondering if anyone
> had managed to using DEM data create hill shading in GRADS?
> 
> I just want my 2d maps to look prettier and give a sense of location by
> adding topography and hill shading.
> 
> Regards Howard 
> 
> 
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