[pgrouting-dev] difference between st_convexhull andpgr_pointsAsPolygon

[Ko Nagase]

Hi list,

I think that removing "Alpha Shape" function from pgRouting,
then moving it to SFCGAL extension may be good for modularity.
(I don't know well about SFCGAL and its PostGIS binding,
but will it be "SFCGAL::algorithm::alphaShape" and "ST_AlphaShape" ?)

In my understanding, PostGIS "ST_ConcaveHull" algorithm is a bit different from
CGAL "Alpha Shape" function, so adding "ST_AlphaShape" (or "ST_Isochrone" ?)
will be necessary in that case.

=====
[ST_ConcaveHull]
http://postgis.net/docs/manual-dev/ST_ConcaveHull.html
[CGAL 4.6 - 2D Alpha Shapes: User Manual]
http://doc.cgal.org/latest/Alpha_shapes_2/index.html
=====

Also, porting osrm-isochrone to PostGIS itself may be an another possibility.

2015-04-10 4:44 GMT+09:00 Stephen Woodbridge <woodbri at swoodbridge.com>:
> FYI. Here is a driving distance tools based on NodeJs that is part of
> mapbox.
>
> https://github.com/mapbox/osrm-isochrone

Just my idea.

Regards,


2015-04-15 23:34 GMT+09:00 Stephen Woodbridge <woodbri at swoodbridge.com>:
> On 4/15/2015 10:33 AM, Paragon Corporation wrote:
>>
>>
>>>   Dropping the CGAL dependency is somewhat less important these days
>>
>> because I believe that postgis now has a dependency on that for some part
>> of
>> the raster code. It used to be a pain for users build with
>>>
>>> that, but it has gotten better package support now that it is getting
>>> used
>>
>> in other GIS packages.
>>
>> The CGAL dependency in PostGIS is not for raster but the SFCGAL extension
>> to
>> PostGIS for 3D support.  It will probably get much more traction in
>> PostGIS
>> 2.2., but right now I don't think in PostGIS  2.1 any shipped
>> distributions
>> are building with SFCGAL support.  So probably at least a concern for
>> PostGIS 2.1 and below.
>
>
> Regina,
>
> Thanks, I remember it was for something that was coming but just was sure
> what.
>
> Anyway, being able to get the points out of driving distance and then
> generating the contour lines using just postgis would be an interesting
> example and if the performance is reasonable then it might be a good
> replacement or alternative to the existing code and just use postgis instead
> for creating the isochrone contours.
>
> -Steve
>
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-- 
Ko Nagase (長瀬　興)
Georepublic Japan
mail: nagase at georepublic.co.jp
web: http://georepublic.co.jp