[GRASS-dev] [GRASS GIS] #2714: wish: logarithmic legend for raster maps

GRASS GIS trac at osgeo.org
Mon Jul 20 07:27:25 PDT 2015

#2714: wish: logarithmic legend for raster maps
 Reporter:  veroandreo   |      Owner:  grass-dev@…
     Type:  enhancement  |     Status:  new
 Priority:  normal       |  Milestone:  7.0.1
Component:  Display      |    Version:  svn-releasebranch70
 Keywords:  d.legend     |        CPU:  x86-64
 Platform:  All          |

 I have several raster maps of chlorophyll concentration (mg/m3) with
 mostly very small values (from 0.02 to 1.5) and few high values (between
 20 and 100). When I use d.legend, as it linearly scales values from
 minimum to maximum, I cannot see variation in colors in those values I'm
 interested most, but the gradient almost only shows variation in higher
 values, which again, are the minority (see file attached).

 Wish: A flag for logarithmic display of legend values or at least the
 possibility to set tick marks at desired values, i.e.: 0.01,0.1,1,10,100
 (without loosing the continuos gradient, as in #1147) would be really
 appreciated in terms of visualization.

 r.colors with logarithmic flag or transforming the raster to logarithm
 does not solve this issue, and one may not be interested in the logarithm
 of the variable, either, but just getting a good visualization of colors.

 The problem is also seen in the manual of r.flow
 (http://grass.osgeo.org/grass71/manuals/r.flow.html#example). The third
 map is mostly "yellowish" but that color does not appear in the legend.

 Thanks much in advance!

Ticket URL: <https://trac.osgeo.org/grass/ticket/2714>
GRASS GIS <http://grass.osgeo.org>

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