[Django] #23022: Geodjango transform introduces large errors

[Django]

#23022: Geodjango transform introduces large errors
----------------------------------+--------------------
Reporter: gabriel.rosser@… | Owner: nobody
Type: Bug | Status: new
Component: GIS | Version: 1.6
Severity: Normal | Keywords: gis
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 1 | UI/UX: 0
----------------------------------+--------------------
Django 1.6.2

Summary:
Geodjango's .transform() method works as expected on GEOS geometry
objects. Small numerical rounding errors appear, as expected. However,
attempting to save a GEOS point with a given SRID to a table with a
different SRID leads to some kind of implicit transform call that
introduces much more significant and problematic numerical errors.

Minimal working example and further details posted here:
http://gis.stackexchange.com/questions/106757/geodjango-transform-
introduces-large-errors

--
Ticket URL: <https://code.djangoproject.com/ticket/23022>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.

[Django]

#23022: Geodjango transform introduces large errors

----------------------------------+--------------------------------------

Reporter: gabriel.rosser@… | Owner: nobody
Type: Bug | Status: new
Component: GIS | Version: 1.6

Severity: Normal | Resolution:

Keywords: gis | Triage Stage: Unreviewed

Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0

Easy pickings: 1 | UI/UX: 0

----------------------------------+--------------------------------------
Changes (by manologab):

* needs_better_patch: => 0
* needs_tests: => 0
* needs_docs: => 0

Comment:

I was unable to reproduce the problem using your example in stackexchange.

{{{
m = MyGeoClass(point=geos.Point([527860, 184660], srid=27700))
m.save()
m = MyGeoClass.objects.get(pk=m.id)
self.stdout.write("Point Created, srid:{}, coords:
{!r}".format(m.point.srid, m.point.coords))

m.point.transform(4326)
m.save()
m = MyGeoClass.objects.get(pk = m.id)
self.stdout.write("Point Changed, srid:{}, coords:
{!r}".format(m.point.srid, m.point.coords))
}}}

Result:
{{{
Point Created, srid:27700, coords: (527860.0, 184660.0)
Point Changed, srid:27700, coords: (527860.0008806133, 184659.99951259216)
}}}

Maybe the problem is in the software versions? I have:

Django 1.6.5
PostGIS 2.1.2

--
Ticket URL: <https://code.djangoproject.com/ticket/23022#comment:1>

[Django]

#23022: Geodjango transform introduces large errors

----------------------------------+--------------------------------------
Reporter: gabriel.rosser@… | Owner: nobody
Type: Bug | Status: closed
Component: GIS | Version: 1.6
Severity: Normal | Resolution: worksforme

Keywords: gis | Triage Stage: Unreviewed

Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0

Easy pickings: 0 | UI/UX: 0
----------------------------------+--------------------------------------
Changes (by timo):

* status: new => closed
* resolution: => worksforme
* easy: 1 => 0

Comment:

Gabriel, could check if there is a similar test in Django's test suite or
try to add one? We can at least check against the software installed on
our continuous integration server to see if it passes. I am going to close
the ticket for now since someone else was unable to reproduce the issue.
Please reopen when/if you can provide more details, thanks!

--
Ticket URL: <https://code.djangoproject.com/ticket/23022#comment:2>