[GRASS-dev] SRTM plus color table
Michael Barton
Michael.Barton at asu.edu
Sun Jan 27 23:04:24 PST 2013
I agree with your comment about the current SRTM color scheme being too brown.
Here is a little tweak that seems to do a better job in displaying topographic variability. It keeps the green tones for a little higher in elevation. It also gets to white at high elevations a little sooner, and then goes to a glacial bluish for the highest peaks to differentiate them.
The links are a comparison between the current and the tweaked "SRTM" color table for the Mediterranean and W. Europe. I scanned it in Asia and the Americas too and it seems an improvement to me. What do you and others think?
Current SRTM land color: https://www.dropbox.com/s/en4117ll4phnak7/srtm1.png
Tweaked SRTM land color: https://www.dropbox.com/s/9hmji9g6nre9klu/srtm2.png
Here is the color table, including both the tweaked land colors and the sea floor colors.
-11000 0:0:0
-8000 0:0:50
-5000 10:10:100
-3000 30:30:150
-1000 70:70:200
-100 100:100:225
0 150:150:255
0.1 57:151:105
100 117:194:93
500 230:230:128
1000 202:158:75
2000 185:154:100
3000 220:220:220
5000 255:255:255
8850 100:100:255
nv 255:255:255
default 255:255:255
____________________
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)
fax: 480-965-7671 (SHESC), 480-727-0709 (CSDC)
www: http://www.public.asu.edu/~cmbarton, http://csdc.asu.edu
On Jan 27, 2013, at 10:27 PM, Michael Barton <michael.barton at asu.edu>
wrote:
> PS: Here's what the color table looks like in an area nearer to you.
>
> https://www.dropbox.com/s/s76xmb7yqz3qgox/Sahul.png
>
> 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)
> fax: 480-965-7671 (SHESC), 480-727-0709 (CSDC)
> www: http://www.public.asu.edu/~cmbarton, http://csdc.asu.edu
>
>
>
>
> On Jan 27, 2013, at 10:18 PM, Michael Barton <Michael.Barton at asu.edu>
> wrote:
>
>> I agree with your synopsis.
>>
>> I started with the ETOPO2 ocean colors to see if I could improve them somewhat.
>>
>> I substituted your rule for the one I had for -100. Good on the continental shelf, but it still looked too dark in the deeps. Here is a little more modification.
>>
>> There are various ways of tweaking color tables for particular locales. I'm looking for something of a compromise that works reasonably well for most ocean depths. Probably not really possible, but I thought I'd play around with it some. I think this one is an improvement over what I did earlier.
>>
>> -11000 0:0:0
>> -8000 0:0:50
>> -5000 10:10:100
>> -3000 30:30:150
>> -1000 70:70:200
>> -100 100:100:225
>> 0 150:150:255
>>
>> Just the ocean part.
>>
>> 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)
>> fax: 480-965-7671 (SHESC), 480-727-0709 (CSDC)
>> www: http://www.public.asu.edu/~cmbarton, http://csdc.asu.edu
>>
>>
>>
>>
>>
>> On Jan 27, 2013, at 9:13 PM, Hamish <hamish_b at yahoo.com>
>> wrote:
>>
>>> Michael wrote:
>>>> So, a little trial and error
>>>> experimentation produces this:
>>> ...
>>>> ...with the following color rules.
>>>>
>>>> -11000 0:0:0
>>>> -8000 0:0:50
>>>> -5000 10:10:70
>>>> -3000 30:30:100
>>>> -1000 70:70:170
>>>> -100 100:100:200
>>>> 0 150:150:255
>>>> 0.1 57:151:105
>>>> 100 117:194:93
>>>> 200 230:230:128
>>>> 500 202:158:75
>>>> 1000 214:187:98
>>>> 2000 185:154:100
>>>> 3000 220:220:220
>>>> 5000 250:250:250
>>>> 8850 255:255:255
>>>> nv 255:255:255
>>>> default 255:255:255
>>>
>>> I'll respond the long way, with some personal cosmetic
>>> observations and critique on ocean colors. YMM(& probably will)V.
>>>
>>> my test data is the etopo1 global elevation dataset.
>>> See Global Datasets on the grass wiki for links.
>>>
>>> r.colors etopo1 color=<>
>>>
>>> etopo2 -- ocean colors are not too bad. land colors much too
>>> green then harsh transition to white.
>>>
>>>
>>> srtm -- only the shallow shelves are visible, most of the ocean
>>> is black. Georges Bank off Cape Cod and the North & Baltic Seas
>>> show up quite well (often < 100m). ~600m is already black, but
>>> for a global view 3000m should still be visible. I find srtm on
>>> land to be too brown, but in coastal areas it can look ok, e.g.:
>>> http://adhoc.osgeo.osuosl.org/livedvd/docs/_images/grass-fractal.png
>>>
>>>
>>> elevation -- relative % based, only intended for land.
>>>
>>>
>>> terrain -- a mix of the green from etopo2 with the black oceans
>>> of srtm! worst of both worlds? elevation based.
>>>
>>>
>>> haxby -- specifically created by W.F. Haxby for highlighting
>>> terrain on the sea floor, but for segments of the sea -- not
>>> the full range. See also "Digital images of combined oceanic and
>>> continental data sets and their use in tectonic studies" in AGU's
>>> EOS from a couple months ago:
>>> http://onlinelibrary.wiley.com/doi/10.1029/EO064i052p00995/abstract
>>> The haxby rules are relative % based scale, so you need to crop
>>> out the ocean first:
>>> r.mapcalc "etopo1.sea = if(etopo1 <= 0, etopo1, null())"
>>> r.mapcalc "etopo1.land = if(etopo1 >= 0, etopo1, null())"
>>>
>>> (but even then the scale is too wide, just zoom in on one part
>>> of the ocean floor to use them)
>>>
>>>
>>> SRTMplus -- the shallow seas have a rather coral-reef look to
>>> them, structure of the deep sea seems a bit blurred out.
>>>
>>>
>>> proposed (above/dropbox'd): the moonlight effect of the sea
>>> floor is nice, although it's a little bit purplish. You can see
>>> a bit more structure in the Baltic, and still some structure on
>>> Georges Bank and the Hudson Canyon. Around the Bahamas the
>>> transitions are a bit harsh. Like "srtm" I find the land to be
>>> too brown for my taste.
>>>
>>>
>>> One thing I often do with ocean floor plots is to put the land in
>>> greyscale, or as a greyscale shaded relief, with the blue->black
>>> ocean. That bypasses any high desert vs. ice cap coloring issues.
>>> (shaded relief works best in a non-LL projection)
>>>
>>> d.erase 60:60:60
>>> r.colors etopo1.sea color=etopo2
>>> d.rast -o etopo1.sea
>>> d.rast -o etopo1.land.shade # lowered resolution to 0:05 during creation else it looks to granular
>>>
>>>
>>> in summary, etopo2 is my favourite for the deep oceans, but may
>>> be too bright if you are strictly looking at the upper 100m of the
>>> continental shelves, in that case "srtm" may be better.
>>>
>>> adding the following 100m rule to "etopo2" seems to look nice for
>>> adding detail in the shallow seas: (e.g. east coast of the US
>>> and the North/Baltic Seas)
>>>
>>> -100:100:100:225
>>>
>>> (see attached screenshot; but you really need to zoom into a
>>> shallow sea like the Bay of Fundy or the Baltic to really see
>>> the difference) It makes the Med look pretty nice too, but that
>>> already looked nice with the "etopo2" rules.
>>>
>>> I propose to add the above rule to "etopo2".
>>>
>>>
>>> regards,
>>> Hamish
>>>
>>>
>>> -----
>>> fwiw,
>>> G> r.univar etopo1.sea -e percent=0,10,20,30,40,50,60,70,80,90,100
>>> minimum: -10803
>>> maximum: 0
>>> range: 10803
>>> mean: -3433.38
>>> standard deviation: 1716.47
>>> ...
>>> 0th percentile: -10803
>>> 10th percentile: -5286
>>> 20th percentile: -4902
>>> 30th percentile: -4532
>>> 40th percentile: -4226
>>> 50th percentile: -3890
>>> 60th percentile: -3509
>>> 70th percentile: -2958
>>> 80th percentile: -1863
>>> 90th percentile: -253
>>> 100th percentile: 0
>>> <etopo1_shaded_relief2.jpg>
>>
>
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