[GRASS-dev] integrate v.concave.hull into v.hull [was point cloud analysis: new features]]

[Moritz Lennert]

On 22/03/15 21:37, Markus Neteler wrote:
> On Sun, Jan 11, 2015 at 9:03 PM, Markus Metz
> <markus.metz.giswork at gmail.com> wrote:
>> On Fri, Jan 9, 2015 at 9:35 AM, Moritz Lennert wrote:
>>> On 08/01/15 23:46, Markus Metz wrote:
>>>>
>>>> On Mon, Jan 5, 2015 at 12:17 PM, Benjamin Ducke  wrote:
>>>>> Thanks Markus, this is excellent progress.
>>>>> It seems to me that the approximation of cluster shapes from grouped
>>>>> points is a generic problem that would best be solved with a separate
>>>>> module. As long as the shapes are roughly convex, the existing v.hull
>>>>> should work fine. For concave shapes, AFAIK things become messy because
>>>>> common methods such as alpha shapes require the user to provide
>>>>> threshold values.
>>>>
>>>> This is true, but v.concave.hull [0] could help ;-)
>>>
>>> All these great addons !
>>>
>>> For this particular one: would it be interesting / possible to integrate it
>>> directly into v.hull ?
>>
>> No, because v.hull is a C module and v.concave.hull a script which
>> does not use v.hull at all. Instead, v.concave.hull cleans the output
>> of v.delaunay to create concave hulls.
>
> I have a similar problem: imagine a set of contour lines which
> describe the bathymetry of a lake, so essentially contour lines which
> are closing a polygon but consist of different lines.

I'm not sure I completely understand the situation, maybe an image would 
help.

>
> I would like to get the respective polygon representation, i.e. the
> outer lines only and those turned into a polygon.
>
> I just tried v.concave.hull on it, however, it expects points and not lines.
> Does anyone have an idea how to achieve that?

I take it that there are no attributes (e.g. depth) linked to the lines ?

Otherwise, maybe v.to.points + v.concave.hull + v.select ?

Or, manually, using the new "Select vector feature(s)" tool in the Map 
Display ?

Moritz