[GRASS-dev] geodesic distances for measuring and buffers, even when working in planar coordinate system ? [was: Re: [GRASS-user] What distance is being measured and used for buffers ?]

[Moritz Lennert]

On 07/09/12 09:05, Markus Metz wrote:
> On Tue, Sep 4, 2012 at 6:57 PM, Moritz Lennert
> <mlennert at club.worldonline.be>  wrote:
>> On 01/09/12 18:02, Moritz Lennert wrote:
>>>
>>> Leaving below mail as record of my original issue, I would to raise the
>>> fundamental question of whether it would be feasible
>>>
>>> 1) to (optionally) provide geodesic instead of planar distances when
>>> measuring, even if the location is in a projected coordinate system.
>>> E.g. QGIS provides the possibility in distance measuring to check a box
>>> to activate geodesic distance
>>>
>>> 2) to (optionally) allow the creation of buffers based on geodesic
>>> distances, again in a projected location, which would imply non-circular
>>> buffers.
>>>
>>
>> Exploring my exploration of this in the hope that someone might share an
>> interest:
>>
>> r.buffer actually provides the possibility of geodesic buffering when used
>> in a lat-long location. Would it be difficult to implement the same in
>> v.buffer ?
>
> The short answer is yes, it will be difficult. The GRASS-internal
> vector buffering algorithm has a number of bugs, the only vector
> buffering method that is AFAICT bug-free is v.buffer in trunk with
> GEOS support which uses the GEOS buffering algorithm which in turn
> does not (yet?) support geodesic distances in latlong.

Ok, thanks for the answer. This means that efforts should be put into 
including this into GEOS and in the mean time, maybe write a small 
script v.buffer.geodesic that uses r.buffer.

Since we're on it: any idea about question 1) ?

Moritz