[Django] #25498: PostGIS Distance lookups use ST_Distance_Sphere() and not ST_Distance()
Django
-------------------------------+--------------------
Reporter: iambibhas | Owner: nobody
Type: Bug | Status: new
Component: Documentation | Version: master
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------+--------------------
Currently
[https://docs.djangoproject.com/en/1.8/ref/contrib/gis/geoquerysets
/#distance-gt the doc says] that PostGIS uses `ST_Distance()` for distance
lookups like `distance_gte` etc. But actually `ST_Distance_Sphere()` is
used. We need to fix that on the doc.
The doc also says in the beginning -
{{{
... an optional third element, 'spheroid', may be included to tell
GeoDjango to use the more accurate spheroid distance calculation functions
on fields with a geodetic coordinate system (e.g., ST_Distance_Spheroid
would be used instead of ST_Distance_Sphere).
}}}
But then `ST_Distance_Sphere` is not mentioned anywhere else.
Here is what currently is happening -
{{{
current_localities = Locality.objects.filter(centroid__distance_lte=(pnt,
1000))
}}}
results in -
{{{
(0.005) SELECT "map_locality"."id", "map_locality"."name",
"map_locality"."slug", "map_locality"."centroid", "map_locality"."radius"
FROM "map_locality" WHERE ST_Distance_Sphere("map_locality"."centroid",
ST_GeomFromEWKB('\x0101000020e6100000865ad3bce3685340e9b7af03e7ec2940'::bytea))
<= 1000 LIMIT 21;
args=(<django.contrib.gis.db.backends.postgis.adapter.PostGISAdapter
object at 0x7fdcc9d320d0>, 1000)
}}}
Attaching a patch with the issue. I can send a PR.
--
Ticket URL: <https://code.djangoproject.com/ticket/25498>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
Django
Reporter: iambibhas | Owner: nobody
Type: Bug | Status: new
Component: Documentation | Version: master
Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Easy pickings: 0
UI/UX: 0 |
Changes (by iambibhas):
* Attachment "doc_gis_distance.patch" added.
patch to rename st_distance to st_distance_sphere
Django
Reporter: iambibhas | Owner: nobody
Type: Bug | Status: new
Component: Documentation | Version: master
Keywords: | Triage Stage: Unreviewed
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
Changes (by iambibhas):
* needs_better_patch: => 0
* has_patch: 0 => 1
* needs_tests: => 0
* needs_docs: => 0
--
Ticket URL: <https://code.djangoproject.com/ticket/25498#comment:1>
Django
Reporter: iambibhas | Owner: nobody
Type: Bug | Status: new
Component: Documentation | Version: master
Keywords: | Triage Stage: Unreviewed
Has patch: 1 | Needs documentation: 0
Easy pickings: 0 | UI/UX: 0
Description changed by iambibhas:
Old description:
> Currently
> [https://docs.djangoproject.com/en/1.8/ref/contrib/gis/geoquerysets
> /#distance-gt the doc says] that PostGIS uses `ST_Distance()` for
> distance lookups like `distance_gte` etc. But actually
> `ST_Distance_Sphere()` is used. We need to fix that on the doc.
>
> The doc also says in the beginning -
>
> {{{
>
> ... an optional third element, 'spheroid', may be included to tell
> GeoDjango to use the more accurate spheroid distance calculation
> functions on fields with a geodetic coordinate system (e.g.,
> ST_Distance_Spheroid would be used instead of ST_Distance_Sphere).
>
> }}}
>
> But then `ST_Distance_Sphere` is not mentioned anywhere else.
>
> Here is what currently is happening -
>
> {{{
> current_localities = Locality.objects.filter(centroid__distance_lte=(pnt,
> 1000))
> }}}
>
> results in -
>
> {{{
> (0.005) SELECT "map_locality"."id", "map_locality"."name",
> "map_locality"."slug", "map_locality"."centroid", "map_locality"."radius"
> FROM "map_locality" WHERE ST_Distance_Sphere("map_locality"."centroid",
> ST_GeomFromEWKB('\x0101000020e6100000865ad3bce3685340e9b7af03e7ec2940'::bytea))
> <= 1000 LIMIT 21;
> args=(<django.contrib.gis.db.backends.postgis.adapter.PostGISAdapter
> object at 0x7fdcc9d320d0>, 1000)
> }}}
>
> Attaching a patch with the issue. I can send a PR.
New description:
Currently
[https://docs.djangoproject.com/en/1.8/ref/contrib/gis/geoquerysets
/#distance-gt the doc says] that PostGIS uses `ST_Distance()` for distance
lookups like `distance_gte` etc. But actually `ST_Distance_Sphere()` is
used. We need to fix that on the doc.
The doc also says in the beginning -
... an optional third element, 'spheroid', may be included to tell
GeoDjango to use the more accurate spheroid distance calculation functions
on fields with a geodetic coordinate system (e.g., `ST_Distance_Spheroid`
would be used instead of `ST_Distance_Sphere`).
But then `ST_Distance_Sphere` is not mentioned anywhere else.
Here is what currently is happening -
{{{
current_localities = Locality.objects.filter(centroid__distance_lte=(pnt,
1000))
}}}
results in -
{{{
(0.005) SELECT "map_locality"."id", "map_locality"."name",
"map_locality"."slug", "map_locality"."centroid", "map_locality"."radius"
FROM "map_locality" WHERE ST_Distance_Sphere("map_locality"."centroid",
ST_GeomFromEWKB('\x0101000020e6100000865ad3bce3685340e9b7af03e7ec2940'::bytea))
<= 1000 LIMIT 21;
args=(<django.contrib.gis.db.backends.postgis.adapter.PostGISAdapter
object at 0x7fdcc9d320d0>, 1000)
}}}
Attaching a patch with the issue. I can send a PR.
--
--
Ticket URL: <https://code.djangoproject.com/ticket/25498#comment:2>
Django
Reporter: iambibhas | Owner: nobody
Type: Bug | Status: new
Component: Documentation | Version: master
Keywords: | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Easy pickings: 0 | UI/UX: 0
Changes (by claudep):
* needs_better_patch: 0 => 1
* stage: Unreviewed => Accepted
Comment:
You are right in that the documentation is not up-to-date. However, it's a
bit more complicated than that. The real function used depends on the type
of the geometry field in the database. You can see the logic here:
https://github.com/django/django/blob/master/django/contrib/gis/db/backends/postgis/operations.py#L39
If the field is geodetic (latitude/longitude), `ST_Distance_Sphere` is
used by default (with spheroid as an option). If the field has projected
coordinates, `ST_Distance` is used by default.
--
Ticket URL: <https://code.djangoproject.com/ticket/25498#comment:3>
Django
Reporter: iambibhas | Owner: nobody
Type: Bug | Status: new
Component: Documentation | Version: master
Keywords: | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 1
Comment (by iambibhas):
Replying to [comment:3 claudep]:
> If the field is geodetic (latitude/longitude), `ST_Distance_Sphere` is
used by default (with spheroid as an option). If the field has projected
coordinates, `ST_Distance` is used by default.
By `geodetic` do you mean a Point type geometry field using SRID 4326? In
my example above, `centroid` is of type `geometry(Point,4326)`.
Just trying to get a clear idea about it.
--
Ticket URL: <https://code.djangoproject.com/ticket/25498#comment:4>
Django
Reporter: iambibhas | Owner: nobody
Type: Bug | Status: new
Component: Documentation | Version: master
Keywords: | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 1
Comment (by claudep):
Yes, 4326 is geodetic in the sense that coordinates (latitude/longitude)
are measured in angles based on an ellispoid representation of the earth.
On the other hand, projected systems are measured in meters or miles based
on a projected plane of the earth (generally only accurate on limited
areas).
--
Ticket URL: <https://code.djangoproject.com/ticket/25498#comment:5>
Django
Reporter: iambibhas | Owner: nobody
Type: Bug | Status: new
Component: Documentation | Version: master
Keywords: | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 1
Comment (by iambibhas):
So maybe we can say something like -
PostGIS: `ST_Distance_Sphere(poly, geom) <= 5` when SRID 4326 is
used
PostGIS: `ST_Distance(poly, geom) <= 5` when any other projected
projected coordinates are used
in 2 different rows. Or use a single row to say both of them.
--
Ticket URL: <https://code.djangoproject.com/ticket/25498#comment:6>
Django
Reporter: iambibhas | Owner: nobody
Type: Bug | Status: new
Component: Documentation | Version: master
Keywords: | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 1
Comment (by claudep):
What about that ?
https://github.com/django/django/pull/5418
--
Ticket URL: <https://code.djangoproject.com/ticket/25498#comment:7>
Django
Reporter: iambibhas | Owner: nobody
Type: | Status: new
Cleanup/optimization |
Component: Documentation | Version: master
Severity: Normal | Resolution:
Keywords: | Triage Stage: Ready for
| checkin
Has patch: 1 | Needs documentation: 0
Easy pickings: 0 | UI/UX: 0
Changes (by timgraham):
* needs_better_patch: 1 => 0
* type: Bug => Cleanup/optimization
* stage: Accepted => Ready for checkin
--
Ticket URL: <https://code.djangoproject.com/ticket/25498#comment:8>
Django
Reporter: iambibhas | Owner: nobody
Type: | Status: closed
Cleanup/optimization |
Component: Documentation | Version: master
Severity: Normal | Resolution: fixed
Keywords: | Triage Stage: Ready for
| checkin
Has patch: 1 | Needs documentation: 0
Easy pickings: 0 | UI/UX: 0
Changes (by Claude Paroz <claude@…>):
* status: new => closed
* resolution: => fixed
Comment:
In [changeset:"617b1a21f5a661ef44030c1662440cc5be158ec0" 617b1a2]:
{{{
#!CommitTicketReference repository=""
revision="617b1a21f5a661ef44030c1662440cc5be158ec0"
Fixed #25498 -- Documented ST_Distance/ST_Distance_Sphere difference
Thanks Bibhas Debnath for the report and Tim Graham for the review.
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/25498#comment:9>
Django
Reporter: iambibhas | Owner: nobody
Type: | Status: closed
Cleanup/optimization |
Component: Documentation | Version: master
Severity: Normal | Resolution: fixed
Keywords: | Triage Stage: Ready for
| checkin
Has patch: 1 | Needs documentation: 0
Easy pickings: 0 | UI/UX: 0
Comment (by Claude Paroz <claude@…>):
In [changeset:"66319cc59724ae28917eea62643d07cc9606897d" 66319cc5]:
{{{
#!CommitTicketReference repository=""
revision="66319cc59724ae28917eea62643d07cc9606897d"
[1.9.x] Fixed #25498 -- Documented ST_Distance/ST_Distance_Sphere
difference
Thanks Bibhas Debnath for the report and Tim Graham for the review.
Backport of 617b1a21f from master.
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/25498#comment:10>