[GRASS-dev] SRTM plus color table

[Michael Barton]

The last one, the NOAA elevation + ice looks especially great for land and sea combination. If we could do something along those lines, it would be outstanding. But you're right. It will take some kind of histogram equalization, at least for the deep ocean.

Michael
____________________
C. Michael Barton
Director, Center for Social Dynamics & Complexity 
Professor of Anthropology, School of Human Evolution & Social Change
Arizona State University

voice: 	480-965-6262 (SHESC), 480-727-9746 (CSDC)
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www: http://www.public.asu.edu/~cmbarton, http://csdc.asu.edu











On Jan 27, 2013, at 3:27 PM, Hamish <hamish_b at yahoo.com>
 wrote:

> Michael wrote:
>> GRASS has a lot of nice pre-defined color tables. But one that is
>> lacking is an SRTM-plus color table. This uses the SRTM color table
>> for land, but has enough contrast to also show the sea floor.
>> Currently, only ETOPO2 has a decent color table for the sea floor,
>> but it is so light in shallow water that the land/sea boundary is not
>> easily discernible if combined with the STRM land colors. So here is
>> an attempt to find a combination of SRTM land, plus a pleasing sea
>> floor color table. Maybe someone can improve on it more. In any case,
>> I'd like to suggest that something along this line be incorporated
>> into the stock pre-defined color tables in GRASS.
> [...]
>> ---- SRTM plus color table -----
>> -11000 0:0:0
>> -5000 0:0:70
>> -1000 0:10:130
>> -50 0:70:225
>> 0 0:191:191
> 
> 
> Hi,
> 
> I fully agree that our deep sea colors need some work. The main
> problem with that is if you wish to focus on the continental
> shelves or the deep trenches. Almost all of the ocean floor is
> shallower than 3000m, but there's the occasional dip to 10-11 km.
> Also most of the continental shelf is shallower than 150-200m.
> So a linear color scale doesn't work for all of that range without
> either blurring out the detail in the shelf, or making everything
> below 3km black. IIRC the old etopo and srtm color rules had one
> focusing on the shelf and the other on the deep sea, but both
> could be improved. (when it is just global elevation it seems
> a little odd to name the rules after the datasource, unless the
> rules came directly from them of course)
> 
> Perhaps a numerical approach is to mask off the elevation < 0 in
> one of the global datasets and run 'r.colors -e' to find the nice
> transitions? Probably some tweaks still needed by hand to make
> sure the shelf breaks are still highlighted.
> 
> 
> I would note that this one:
>   http://grassold.osgeo.org/screenshots/images/earthquakes_small2.jpg
> 
> is the same as this,
>   http://grass.fbk.eu/spearfish/earthquakes_small.jpg
> 
> just with the rules bumped to up the contrast, as I find the
> default (observational) Blue Marble 2000 too dark.
> 
> And fwiw these were taken from NOAA's elevation + ice hybrid rules:
>   http://adhoc.osgeo.osuosl.org/grass/earthquakes.png
> but again a supplied R,G,B band image, not mathematical rules.
> 
> 
> summary: a straight linear set of rules are not enough, for
> best results we might need to do a histogram scale for the above
> and below the shelf break, and somehow cleanly transition those
> two together.
> 
> Also finding something which is nice on the computer monitor,
> even when the colors are washed out on a presentation projector,
> and still nice when printed to a page in black and white is
> possible, but not always so easy to do.
> 
> 
> best,
> Hamish