On 09/09/12 16:34, Markus Metz wrote:
On Fri, Sep 7, 2012 at 9:45 AM, Moritz Lennert
<mlenn...@club.worldonline.be> wrote:
On 07/09/12 09:05, Markus Metz wrote:
On Tue, Sep 4, 2012 at 6:57 PM, Moritz Lennert
<mlenn...@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) ?
I guess this feature would need to be implemented on both library and
module level. A library function to first project to latlong, then
calculate geodesic distance would be needed. Modules could then get an
option to use geodesic distance, as long as it is not a pseudo xy
projection, and make use of the new library function if requested.
There may be a lot of pitfalls with such a feature.
Would it be at least possible to enable this in the measurement tool in
the GUI without having to modify many modules or libraries ?
Just brainstorming...
Moritz
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