[JPP-Devel] [Fwd: Re: [postgis-users] Using a buffer with a LineString covering the whole world]

[Matthes Rieke]

Hey again,

thanks for so many interesting comments! the problem with defining my
projection is that i do not know the actual LineString before buffering. It
can be from france to usa, or from france to sweden and then to usa (the
LineStrings are flight routes and might change). So i think the only
suitable solution for me is to split the LineString into single LineStrings
fitting different UTM zones and do a union on those in wgs84. but i think i
will get a buffer with gaps in it.. hmm. not the best but a working
solution!

regards,
Matthes


2009/2/11 Stefan Steiniger <sstein at geo.uzh.ch>

> As I am not on the postgis list I answer directly to Matthes,
>
> the solution is - maybe - simple.
> Define your own projection and buffer there. I would say it should be a
> Cylindric Projection (Oblique Mercator) which is touching/based on the great
> circle that runs between both cities. It would be similar to the swiss
> projection but with different origin and different azimuth:
>
> http://www.swisstopo.admin.ch/internet/swisstopo/en/home/topics/survey/sys/refsys/projections.html
>
> ok.. maybe it isn't that simple and it will take a few days to realize that
> ;)
>
> stefan
>
> PS: thanks Martin for making aware
>
> PPS: I wonder if I did write a long time pseudo code in Mathcad to display
> the distortion of circles due to the UTM projection. But I may be wrong and
> it have been something else.
>
> Martin Davis wrote:
>
>> Check out this thread on the PostGIS list for more interesting discussion
>> on this topic.
>>
>> I wonder how Oracle would handle the USA-to-France buffer?  Not well, I'm
>> betting...
>>
>> -------- Original Message --------
>> Subject:        Re: [postgis-users] Using a buffer with a LineString
>> covering the whole world
>> Date:   Wed, 11 Feb 2009 08:58:16 -0800
>> From:   Paul Ramsey <pramsey at opengeo.org>
>> Reply-To:       PostGIS Users Discussion <
>> postgis-users at postgis.refractions.net>
>> To:     PostGIS Users Discussion <postgis-users at postgis.refractions.net>
>> References:     <
>> 1e3d99e40902110826m45a27717j3780bac013f0e31b at mail.gmail.com>
>>
>>
>>
>> I find running screaming into the hills helps.
>>
>> Sorry, that's the use case (really large/long things) where there just
>> is no proper solution except to start writing code that works on a
>> sphere. Most things just aren't that long/large.  But a few are. I
>> would love it if someone/manyones would express their interest in
>> funding such a development.
>>
>> Want a hack? Cut your line into 1000 smaller lines. Buffer all those
>> individually in a planar space. The union them all back together
>> again, in lon/lat.
>>
>> P.
>>
>> On Wed, Feb 11, 2009 at 8:26 AM, Matthes Rieke
>> <matthes.rieke.01 at gmail.com> wrote:
>>
>>> Hi all,
>>>
>>> I am currently running into this problem: I have a LineString in lat/long
>>> coordinates (SRID 4326 - going from USA to france). I now want to create
>>> a
>>> buffer in meters from this. So the normal way to transfrom the
>>> coordinates
>>> to a planar CRS, buffering, then transforming back to 4326 does not work
>>> (the Line is covering many UTM zones). What would be a reasonable
>>> solution
>>> for this problem?
>>>
>>> Thanks and regards,
>>> Matthes
>>>
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>>> postgis-users at postgis.refractions.net
>>> http://postgis.refractions.net/mailman/listinfo/postgis-users
>>>
>>>
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>>
>>
>>
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