[GRASS-user] displaying many thematic maps from one vector dataset

Wed Apr 8 13:01:36 EDT 2009

And one more for the wish list on legends:
- a flag to strip off decimal places if the data happens to be float..

On Wed, Apr 8, 2009 at 9:48 AM, Vishal Mehta <vishalm1975 at gmail.com> wrote:

> Hi Moritz,
> Regarding legends with d.graph, these are the main issues where I found I
> needed to do too much of trial and error, some of which I think could
> probably be avoided/improved in a future version...
>
> 1. the legend ends up with some strange additions beyond just the range of
> data: like what are those numbers after each range
> e.g. in the example below where did | 0 and | 5 come from? It would be nice
> to not have this automatically displayed.
> 60 - 80 | 0
> 80-100 | 5
>
> 2. there could be a flag on d.graph, which allows the output to have a "<
> minbreak" and "> maxbreak" option, so that for cases like the one we are
> discussing, the legend does not keep changing based on different data
> ranges.
>
> 3. size and position
> Here, I wanted to get a legend file separately, and save a legend png. To
> do this I had to play with the size and other parameters extensively to make
> the symbols and associated text match up. It would be great to be able to do
> the following with some flags, for the case where the legend alone is
> displayed:
> (i) set the overall size of the display within which the legend will be
> displayed
> (ii) set the position of the legend within the display with options like
> lowerleft, upperright, center, etc
> (iii) set the size of the legend as a fraction/percentage of the display.
> (iv) make the background transparent (or not)
> such that the above settings 'automatically' set up the symbol and
> corresponding text all properly lined up..
>
> I am aware that if I was just better at this I could do it quickly
> enough..but the above functionality would make it easier for
> less-than-expert people like myself, who try to use open-source as much as
> possible despite the handicap of having been groomed on Windows...
>
> I will write back when i've had a chance to look up the segfaults on my
> laptop..
>
> And oh, the mismatch of color between display and legend was entirely my
> fault - i was displaying with one set of colors but had tweaked the legend
> file separately with a different set of colors..
>
> Thanks for all your help,
> Vishal
>
>
> On Wed, Apr 8, 2009 at 4:58 AM, Moritz Lennert <
> mlennert at club.worldonline.be> wrote:
>
>> On 08/04/09 02:23, Vishal Mehta wrote:
>>
>>> Regarding the segmentation faults: I switched to a different machine
>>> to do all this latter work. I havent tried the new scripts on the
>>> original machine (my laptop). Both are running 6.4svn.
>>>
>>
>> Weird. I can confirm segfaults in 6.5svn (I suppose that this is what
>> you mean by 6.4svn, i.e. the current 6.x development branch), but only
>> when using d.mon, not when using direct rendering
>> (GRASS_RENDER_IMMEDIATE=TRUE). Since I wrote this code on the base of
>> the grass7 tree, and then ported it back to 6.x, it is quite probable
>> that I forgot some adaptations needed for d.mons... (CC'ing to Glynn for
>> any pointer on where I should look).
>> Could you try with direct rendering on the machine where it segfaulted
>> with d.mons ?
>>
>>  Regarding legends, I found that I had to play around way too much to
>>> get the legend right.
>>>
>>
>> Could you tell me which were the major parts that needed adjustment from
>> you ?
>>
>> As you want to use the same legend for all maps, it is obviously easier
>> to create one legend file by hand and to call d.graph on that in each
>> cycle of the loop.
>>
>> However, I tweaked the source code (grass7 for now) just very slightly
>> (changing text size and taking into account the case where the min value of
>> the data is above the lowest break (or the max value below the highest break
>> - see 2010-2030 max values in the example) and then ran the following script
>> (using direct rendering as monitors don't exist anymore):
>>
>> export GRASS_FONT=Vera
>> export GRASS_PNG_READ=TRUE
>>
>> yr=2010
>> while [ $yr -lt 2105 ] ;
>>  do
>>    echo "yr is $yr "
>>    export GRASS_PNGFILE=pc$yr.png
>>    d.thematic.area map=CA column=pc$yr breaks=20,40,60\
>>                colors=cyan,yellow,red,blue leg=legfile
>>    d.text -b text="$yr Population" at=50,90 size=4
>>    d.graph in=legfile
>>    if [ $yr -eq 2090 ]
>>       then yr=$((yr+10))
>>       else yr=$((yr+5))
>>    fi
>>  done
>>
>>
>> You can see the resulting animated gif here:
>> http://geog-pc40.ulb.ac.be/popCA.gif
>>
>> I don't find the legends too bad, but obviously it is difficult to create
>> a one-size-fits-all solution for legends. I spent some time trying to find
>> the right algorithm, but it is still very far from perfect. One thing I
>> should probably add is a parameter for the placement of the legend in screen
>> percents. Another is a detection mechanism to see how many significant
>> decimals to keep (There should be some examples, notably in Hamish'es work,
>> I just need to look at those...). I don't know, however, whether the d.graph
>> solution is the best, so feedback is very welcome on that.
>>
>>
>>  And even then, there's a yellow color that is not on the legend file,
>>> that shows up in the display anyway.
>>>
>>
>> Could you show an example of that ?
>>
>> Thank you for your feedback so far. We really have to identify the cause
>> of those segfaults...
>>
>> Moritz
>>
>
>
>
> --
> Vishal K. Mehta, PhD
> Scientist
> Stockholm Environment Institute - US
> 133 D St Suite F
> Davis CA 95616
> www.sei-us.org
>

-- 
Vishal K. Mehta, PhD
Scientist
Stockholm Environment Institute - US
133 D St Suite F
Davis CA 95616
www.sei-us.org
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