[GRASS-dev] all categories copied over to new map

[Paulo van Breugel]

On Thu, Sep 17, 2015 at 11:56 AM, Moritz Lennert <
mlennert at club.worldonline.be> wrote:

> On 16/09/15 10:48, Paulo van Breugel wrote:
>
>>
>>
>> On 16-09-15 09:49, Moritz Lennert wrote:
>>
>>> On 15/09/15 20:08, Paulo van Breugel wrote:
>>>
>>>> Suppose I have a categorical raster map and I want to 'cut out' a subset
>>>> (with g.region to set a small region and r.mapcalc to create the new
>>>> map). This map has a smaller number of categories, as is shown using
>>>> e.g., r.category. However, when plotting the legend, all the categories
>>>> of the original map are included in the legend. Checking the 'cats' file
>>>> shows that it indeed lists all original categories and labels, including
>>>> for those categories not present in the new map. This doesn't make sense
>>>> to me, but perhaps I am missing something here?
>>>>
>>>
>>> AFAIK, the legend is determined by the color table, and the color
>>> table is probably just copied as is from the input to the output map.
>>> You can check with r.colors.out. If you redefine a color table with
>>> only the relevant categories, then the legend should reflect that.
>>>
>>
>> Hi Moritz, that is what I thought, and as the whole color table does
>> indeed get copied over, I wrote a small script to remove the 'redundant
>> color definitions. However, that did not help, the whole 'old' legend is
>> still showing.  I had missed that -n flag, so I'll give that a try. Is
>> there a similar option in ps.map to omit categories without label?
>>
>>   From a more conceptual point of view, is there any reason the whole
>> category table is copied over to the new cats file?
>>
>
> Probably not. IIUC, this only happens when you have a formula of the form
> "new = old".
>
> An easy work around:
>
> r.category new  | r.category new rules=-
>
> The resulting cats file only contains the cats actually present and you
> can thus use d.legend -n to only show those.
>

That is a very neat trick, thanks!

>
> Moritz
>
>
>
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