POINT() and PointField() structures

[CodeCRC]

Hello all,

I use geoDjango for an application based on OpenStreetMap in which
users will be allowed to add POIs related to ecology on a map.
I want to add RSS feeds : an user will be able to follow all the new
POIs in an area he will delimit.
I put the 4 following coordinates in the URL :
- upper_left_lat
- upper_left_lon
- lower_right_lat
- lower_right_lon

This is an example of an URL :

http://127.0.0.1:8000/myapp/rss/area/6141249,-213707,-160201,-160201/

Then, I parse the URL in the feed class and retrieve the 4
coordinates :

###############################################
class LatestPOIsByZone(Feed):

title_template = "rss_title.html"
description_template = "rss_descr.html"

def get_object(self, bits):
if len(bits) != 1:
raise ObjectDoesNotExist
coordinates = str(bits[0]).split(',')

upper_lat = float(coordinates[0])
upper_lon = float(coordinates[1])
lower_lat = float(coordinates[2])
lower_lon = float(coordinates[3])

upper = Point((upper_lat, upper_lon))
lower = Point((lower_lat, lower_lon))

area_coordinates = upper, lower

return area_coordinates
###############################################

Now, I want to return all the POI which are situated in the area
delimited by the two coordinates.
Here is the model of the POIs :

###############################################
class Marker(models.Model):
'''Marker for a POI
'''
name = models.CharField(_("Name"), max_length=150)
subcategory = models.ForeignKey(SubCategory, verbose_name=_
("Subcategory"))
avail_date = models.DateTimeField(_("Available Date"), blank=True,
null=True)
point = PointField(_("Localisation"))
...
###############################################

So I have markers in my database (PointField type) and two coordinates
designated by two POINTS structure (upper-left and lower-right) which
delimit the area. I want to retrieve from the database all the markers
situated in this area.
I think I have to make the request in the 'items(self, obj)' method
but I have no idea how to do such a thing. I have seen in the db
geodjango API requests such as :

Marker.objects.filter(point__contained=area)

Where point is my marker localisation and area a geo object
representing my area.
But I don't know if I can use it in my case and how to use it.

Thanks in advance,

CodeCRC

[Tyler Erickson]

CodeCRC,

Based on what you are trying to do, it seems more natural to store
your area of interest (AOI) as a polygon, rather than two points.
That way you can use the spatial operators to check if points are
within your AOI.

Example:
from django.contrib.gis.geos import GEOSGeometry
AOI=GEOSGeometry('POLYGON(( 10 10, 10 20, 20 20, 20 15, 10 10))')

- Tyler

[J. Cliff Dyer]

On Tue, 2010-01-26 at 14:55 -0800, Tyler Erickson wrote:
> CodeCRC,
>
> Based on what you are trying to do, it seems more natural to store
> your area of interest (AOI) as a polygon, rather than two points.
> That way you can use the spatial operators to check if points are
> within your AOI.
>
> Example:
> from django.contrib.gis.geos import GEOSGeometry
> AOI=GEOSGeometry('POLYGON(( 10 10, 10 20, 20 20, 20 15, 10 10))')
>
> - Tyler

You may also be interested in the from_bbox method of geos Polygons as
well:

>>> top = 20
>>> bottom = 0
>>> left = 100
>>> right = 200
>>> from django.contrib.gis import geos
>>> p = geos.Polygon.from_bbox([left, bottom, right, top])
>>> p.wkt
'POLYGON ((100.0 0.0, 100.0 20.0, 200.0 20.0, 200.0 0.0, 100.0 0.0))'
>>> # WKT trimmed for readability

Cheers,
Cliff