logarithmic scale in raster legend

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logarithmic scale in raster legend

Veronica Andreo
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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Re: logarithmic scale in raster legend

DanielV

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" <[hidden email]> 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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Re: logarithmic scale in raster legend

Veronica Andreo
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 <[hidden email]>:

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" <[hidden email]> 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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Re: logarithmic scale in raster legend

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


On Tue, Jun 10, 2014 at 9:32 AM, Veronica Andreo <[hidden email]> 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 <[hidden email]>:

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" <[hidden email]> 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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Re: logarithmic scale in raster legend

Larry Prevett
In reply to this post by Veronica Andreo
Have you tried using the echo command to pipe variables and characters to d.text  for user defined labels and ticks? It takes some work with the at=x,y coords to get the legend, labels and ticks where you want them.

  echo "message" | d.text size=3 at=37,25 color=orange

  To erase map elements or labels, you can echo dummy characters the same  color as the background:

  echo "##########" | d.text -b size=5 at=18,6 color=white

 You may also want to use a graphics tool (e.g, ImageMagick, convert)
 to do various graphics conversions on the maps.

L. Prevett


On Mon, Jun 9, 2014 at 8:36 AM, Veronica Andreo <[hidden email]> 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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Re: logarithmic scale in raster legend

Veronica Andreo
Hi :)

2014-06-13 14:23 GMT-03:00 L. Prevett <[hidden email]>:
Have you tried using the echo command to pipe variables and characters to d.text  for user defined labels and ticks? It takes some work with the at=x,y coords to get the legend, labels and ticks where you want them.

  echo "message" | d.text size=3 at=37,25 color=orange

Nope, this I haven't tried... i did it just now, and it seems it doesn't work with echo, but as: 

d.text text="bla" at=30,30 size=6 color=red

I'd wish there was a flag or button for this task :-/ 
Thanks for the tips!

Best, 
Vero 
 


On Mon, Jun 9, 2014 at 8:36 AM, Veronica Andreo <[hidden email]> 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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