[GRASS-user] logarithmic scale in raster legend

Daniel Victoria daniel.victoria at gmail.com
Tue Jun 10 05:38:46 PDT 2014


You are correct. Then I have no idea how to do this...


On Tue, Jun 10, 2014 at 9:32 AM, Veronica Andreo <veroandreo at gmail.com>
wrote:

> Yeah, I also tried that, and of course, I get a nice gradient in the
> legend, but then I need to somehow edit tick-marks.
> Logarithm of chlorophyll concentration is, from my point of view,
> uninformative. I need the actual values.
> I just want to change the display of the legend, like making log of x or y
> axis in a plot, that you do not change the
> values themselves, just rescale the axis for better visualization... but
> maybe not (yet) possible in GRASS ;)
>
> Thanks much!
> Vero
>
>
> 2014-06-10 7:40 GMT-03:00 Daniel Victoria <daniel.victoria at gmail.com>:
>
>> What if you use r.mapcalc and apply log to your map to make a new one
>> with rescaled values?
>> On Jun 9, 2014 12:36 PM, "Veronica Andreo" <veroandreo at gmail.com> wrote:
>>
>>> Hi list!
>>>
>>> I have these raster maps of chlorophyll concentration (mg/m3) with a lot
>>> of very small values (from 0.02 to 1.5) and few high values (between 20 and
>>> 100)... I managed to create my own color table to get a good visualization
>>> of the variation... but when I display the legend, i loose the color
>>> variation in smaller values...
>>>
>>> Is it possible to create a logarithmic legend or at least determine
>>> which tick-marks I'm interested in?? I've tried with "use" parameter in
>>> d.legend (which seemed to meet my needs) setting it to: 0.01,0.1,1,10,100,
>>> but works only for categories... There's no such a thing in ps.map,
>>> either... which would be the right approach? any ideas?
>>>
>>> Thanks much in advance!
>>> Best,
>>>
>>> Vero
>>>
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>>>
>>
>
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