[GRASS-user] generalize polygons including holes

[Markus Metz]

On Fri, Feb 6, 2015 at 11:08 AM, Robert Nuske <rnuske at gwdg.de> wrote:
> Hi Markus
>
>> >>>> v.generalize does not distinguish between outer and inner rings, it
>> >>>> simply goes through all boundaries and generalizes each one.
>> >>>
>> >>> And this has always been the case or this is specific to GRASS7 ?
>> >>
>> >> This has always been the case.
>> >
>> > Then why doesn't there seem to be any generalization happening for the
>> > hole
>> > boundaries of the test dataset with grass64release ?
>>
>> With the test dataset you provided, GRASS 6.4 does generalize the hole
>> boundaries. I do not have the problem vector of Robert, so I can not
>> say if the hole boundaries in that vector are generalized or not.
>
> Please find attached a location with a test dataset (snipped of larger vector
> map) and two images from generalizations carried out in GRASS 6.4.4
> (6.4.4-1~trusty5 from ppa:ubuntugis-unstable) and GRASS 7.0
> (7.0.0+1svn64474~ubuntu14.04.1 from ppa:grass-devel).
> Blue layer is generalized and red one is the original both at 50%
> transparency.
>
>
> For me, the results from GRASS 7.0 look as expected (inner rings generalized)
> but v.generalize in GRASS 6.4 seems not to treat inner rings.

Thanks for the test location, I could reproduce it, fixed in relbr64 r64478.

Markus M

>
>
>
> GRASS 6.4.4
> -----------------------------------------------------------
> v.generalize in=test_data out=test_gen method=douglas thresh=5000
>
> Number of vertices for selected lines reduced from 907 to 82 (9%).
> v.generalize complete.
>
>
> GRASS 7.0
> -----------------------------------------------------------
> v.build map=test_data
> v.generalize in=test_data out=test_gen method=douglas thresh=5000
>
> v.generalize complete. Number of vertices for selected features reduced
> from 4605 to 451 (9%).
>
>
>
> cheers,
>   robert