[GRASS-dev] modifying the dblink it require to re-build the topology

[Moritz Lennert]

[Please keep discussions on the list]

On 07/11/13 08:35, Pietro wrote:
> Hi Moritz,
>
> On Tue, Nov 5, 2013 at 5:20 PM, Moritz Lennert
> <mlennert at club.worldonline.be>  wrote:
>>> And what happens to the categories? should I rewrite the categories to
>>> link the new layer with the geometry features? Or if not define the
>>> geometry features inherit the categories from the previous layer?
>>


>
>> If you want to use the same category values in each layer, than you have the
>> "transfer" option in v.category (only grass7) to copy category values from
>> one layer to another.
>
> Ok, I transformed the i.segment results into a vector map, add a table
> with the shape and raster statistics for each segment (segment_data),
> and then I have another table with the class for each segment that I
> want to use for the training (segment_training),
>
> $ v.db.connect -p map=segments at final table=segments_data_training
> Vector map<segments at final>  is connected by:
> layer<1/segments_data>  table<segments_data>  in database
> </data/gis/edi/final/sqlite/sqlite.db>  through driver<sqlite>  with
> key<cat>
> layer<2/segments_data_training>  table<segments_data_training>  in
> database</data/gis/edi/final/sqlite/sqlite.db>  through driver
> <sqlite>  with key<cat>
>
> After the classification I will ad a Table with a classification
> results for each column, or maybe better a new table for each
> classification method. What do you think?
> The problem is when I try to use the v.category module.
>
> $ v.category input=segments option=report
> Layer: 1
> type       count        min        max
> point          0          0          0
> line           0          0          0
> boundary       0          0          0
> centroid 2726635          1    2726635
> area     2726635          1    2726635
> face           0          0          0
> kernel         0          0          0
> all      2726635          1    2726635
> Layer: 2
> type       count        min        max
> point          0          0          0
> line           0          0          0
> boundary  261842          0          0
> centroid       0          0          0
> area           0          0          0
> face           0          0          0
> kernel         0          0          0
> all       261842          0          0
>
> Now I would like to copy the categories, from the layer 1 to layer 2.
> I tried with:
>
> v.category input=segments output=segm option=transfer layer=1,2
>
> Is it not possible to work on the input map without generating a new
> one, isn't it?
> Perhaps we can modify the v.category module, that if output is not
> set, then open the input vector map in read-write mode and update all
> the categories of the input map.
>
> Any way lets check the output:
>
> $ v.category input=segm option=report
> v.category input=segm option=report
> Layer/table: 1/segm_segments_data
> type       count        min        max
> point          0          0          0
> line           0          0          0
> boundary       0          0          0
> centroid 2726635          1    2726635
> area           0          0          0
> face           0          0          0
> kernel         0          0          0
> all      2726635          1    2726635
> Layer/table: 2/segm_segments_data_training
> type       count        min        max
> point          0          0          0
> line           0          0          0
> boundary       0          0          0
> centroid 2726635          1    2726635
> area           0          0          0
> face           0          0          0
> kernel         0          0          0
> all      2726635          1    2726635
>
> All the area are missing... but are missing non only on the categories
> level, they are missing from the output map!
>
> $ v.info segments -t
> nodes=4779720
> points=0
> lines=0
> boundaries=7250355
> centroids=2726635
> areas=2726635
> islands=256000
> primitives=9976990
> map3d=0
> $ v.info segm -t
> nodes=0
> points=0
> lines=0
> boundaries=0
> centroids=2726635
> areas=0
> islands=0
> primitives=2726635
> map3d=0
>
> I'm doing something wrong or is it a bug?

I thought that maybe you forgot to use the type parameter, but I just 
tried in the NC dataset and can confirm your issue:

v.category boundary_county op=report
Layer/table: 1/boundary_county
type       count        min        max
point          0          0          0
line           0          0          0
boundary       0          0          0
centroid     926          1        926
area         926          1        926
face           0          0          0
kernel         0          0          0
all          926          1        926

And then, whatever the combination of types I chose, I get

v.category boundary_county op=transfer out=bc2 layer=1,2

v.category bc2 op=reportLayer/table: 1/bc2
type       count        min        max
point          0          0          0
line           0          0          0
boundary       0          0          0
centroid     926          1        926
area           0          0          0
face           0          0          0
kernel         0          0          0
all          926          1        926
Layer: 2
type       count        min        max
point          0          0          0
line           0          0          0
boundary       0          0          0
centroid     926          1        926
area           0          0          0
face           0          0          0
kernel         0          0          0
all          926          1        926


So I would guess that it's a bug. In the source code, when you look at 
the part for the 'add' option, you see that there is specific code for 
areas. I would guess that the same or similar needs to be added to the 
'transfer' option to make sure that boundaries are also copied into the 
output map.

> Is it not possible to work on the input map without generating a new
> one, isn't it?
> Perhaps we can modify the v.category module, that if output is not
> set, then open the input vector map in read-write mode and update all
> the categories of the input map.

I know that it can be annoying to have to create new maps, but at the 
same time it is a failsafe that makes sure that even if you make a 
mistake in the call to v.category, you still keep your original data.

I think that the overhead of a g.rename --o is a price worth paying for 
that security.

Moritz