[GRASS-user] Add DB entries to vector line (after v.split)

[Ken Nussear]

Thanks very much, that is all working well. I did try the addon you
mention, but using grass7 it wont install in either linux or mac os

I'm having some trouble with the final layer though when trying to
sample a raster....


Using this command

v.what.rast map=TSELinesSplit500_w_lay2 at PERMANENT type=centroid
raster=a250m_ATI at MojaveCovariates_250m column=RC1

WARNING: No record for category 0 in table <TSELinesSplit500_w_lay2>

Any idea why I have no category 0?

Ken
> Moritz Lennert <mailto:mlennert at club.worldonline.be>
> May 7, 2015 at 2:54 AM
> On 06/05/15 22:12, knussear wrote:
>> Interestingly 4 years later and using V.split in grass7 and I'm still
>> having
>> the same problem....
>>
>> tried the v.category solution and the cats were never deleted.
>
> Are you sure ? In the original thread, the check for success was wrong
> [1]: v.db.select checks the attached attribute table (which v.split
> does not modify), not the categories present in the features.
>
> Here's a working example using a simple vector map with three lines:
>
> v.split test_line out=line_test_split length=5000
>
> v.category line_test_split op=report
> Layer/table: 1/line_test_split
> type       count        min        max
> point          0          0          0
> line          46          2          4
> boundary       0          0          0
> centroid       0          0          0
> area           0          0          0
> face           0          0          0
> kernel         0          0          0
> all           46          2          4
>
> Now, two options:
>
> 1) You want to keep the category values of the original lines, but
> also add individual category values for the new segements. Here
> GRASS's layer paradigm comes in handy, allowing you to create a second
> layer of information:
>
> #create second information layer containing new individual category
> values for the segments
> v.category line_test_split out=line_test_split_w_lay2 layer=2 op=add
>
> v.category line_test_split_w_lay2 op=report
> Layer/table: 1/line_test_split_w_lay2
> type       count        min        max
> point          0          0          0
> line          46          2          4
> boundary       0          0          0
> centroid       0          0          0
> area           0          0          0
> face           0          0          0
> kernel         0          0          0
> all           46          2          4
> Layer/table: 2/line_test_split_w_lay2_2
> type       count        min        max
> point          0          0          0
> line          46          1         46
> boundary       0          0          0
> centroid       0          0          0
> area           0          0          0
> face           0          0          0
> kernel         0          0          0
> all           46          1         46
>
> Now you can add a new attribute table to the second layer:
>
> v.db.addtable line_test_split_w_lay2 layer=2
>
> If you want to integrate the old categories (or anything else from the
> original attribute table) into the attribute table of the new segments:
>
> v.db.addcolumn line_test_split_w_lay2 col="old_cat int" layer=2
> v.to.db line_test_split_w_lay2 layer=2 query_layer=1 op=query
> query_col=cat col=old_cat
>
> v.db.select line_test_split_w_lay2 layer=2
> cat|old_cat
> 1|2
> 2|2
> 3|2
> 4|2
> 5|2
> 6|2
> 7|2
> 8|2
> 9|2
> 10|2
> 11|2
> 12|2
> 13|2
> 14|2
> 15|2
> 16|2
> 17|3
> 18|3
> 19|3
> 20|3
> 21|3
> etc...
>
> 2) You just need the segments with individual category values, but not
> the old line categories, nor the old attribute table:
>
> #delete old cats, don't keep old attribute table to avoid confusion
> v.category -t line_test_split op=del cat=-1 out=line_test_split_wo_cats
>
> #add new cats
> v.category line_test_split_wo_cats out=line_test_split_w_new_cats op=add
>
> #now, if necessary create new attribute table prefilled with cat values
> v.db.addtable line_test_split_w_new_cats
>
>> My system
>> will also not install the v.to.equidist add on.
>
> Which version of GRASS are you using. The addon was developed for
> GRASS 6.
>
> It is a simple shell script which you can download from [2], but I
> haven't checked if it will run as-is in GRASS 7
>
>
> Moritz
>
> [1] http://lists.osgeo.org/pipermail/grass-user/2011-October/062318.html
> [2]
> https://raw.githubusercontent.com/amuriy/GRASS-scripts/master/v.to.equidist
>
>
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