[postgis-users] Failing ST_Transform with Ross Ice Shelf polygon
Marco Boeringa
marco at boeringa.demon.nl
Tue Nov 7 11:16:55 PST 2023
Thanks Paul,
But is there a more definitive solution in PostGIS / PROJ on the horizon
in terms of future development? No one expects a perfectly valid
geometry that just happens to hit the projection boundary of WGS1984 to
come out garbled by doing a transform and back-transform to the original
CRS. I realize there may be technical challenges here, but this will
undoubtedly keep coming up many times in the future, and likely has in
the past, by other confused non-expert users of PostGIS if nothing
changes. It is really counter-intuitive to need to use stuff like
ST_SnapToGrid, ST_ReducePrecision or ST_WrapX to "fix" something that
goes right for 99.999% of all other data. It also makes any needed code
more convoluted.
Yes, well, I know, storing data in WGS 1984 geometry may not be best
practice with this kind of globe spanning data, but it works for most
cases and I already cast to geography a lot to do stuff where geography
is really needed.
Marco
Op 7-11-2023 om 19:02 schreef Paul Ramsey:
>
>
>> On Nov 6, 2023, at 3:39 PM, Paul Ramsey <pramsey at cleverelephant.ca>
>> wrote:
>>
>>
>>
>>> On Nov 6, 2023, at 3:33 PM, Marco Boeringa <marco at boeringa.demon.nl>
>>> wrote:
>>>
>>> Well, yes indeed that is what is happening, 180 came out of the
>>> reprojection steps as -180. Full output geometry below. Is there any
>>> way to prevent this behavior?
>>>
>>> Marco
>>>
>>
>> Not really… Either snap to grid or reduce precision
>>
>> https://postgis.net/docs/ST_ReducePrecision.html
>> https://postgis.net/docs/ST_SnapToGrid.html
>>
>> will get you back onto the dividing line (note that it is
>> at -180.00000000000014), but that won’t help in flipping -180 to 180.
>> For your particular case, applying
>>
>> https://postgis.net/docs/ST_ShiftLongitude.html
>>
>> will fix it, I think, though not in generality
>
> I think using
>
> https://postgis.net/docs/ST_WrapX.html
>
> would allow a more general purpose solution. At least one you have
> more control over.
>
> P
>
>>
>> P
>
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