Code

Changes between Version 86 and Version 87 of GeoDjango


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Timestamp:
07/08/07 12:32:51 (7 years ago)
Author:
jbronn
Comment:

added OGRGeometry transform question to FAQ

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  • GeoDjango

    v86 v87  
    8282 * '''Q:''' Per [http://groups.google.com/group/django-developers/browse_thread/thread/9f6c70864bfa7f2e/ this discussion] in {{{django-developers}}}, "I can do spatial queries if they are directly between two models with polygon fields but I can't seem to get at the spatial queries through foreign keys." 
    8383   * Geographic queries require {{{GeoManager}}}, even if the model does not have a geographic field itself (in the case of a foreign key to a geo-field).  The reply in the discussion gives detail into why. 
     84 * '''Q:''' Why are the OGRGeometry methods {{{transform}}} and {{{transform_to}}} separate? 
     85   * Because these map to the separate OGR routines [http://www.gdal.org/ogr/ogr__api_8h.html#59a5b3f954b11cfbf6e78807c28d6090 OGR_G_Transform] and [http://www.gdal.org/ogr/ogr__api_8h.html#43af4c2127cea0a5059692a62c0feb63 OGR_G_TransformTo].  Specifically, the {{{transform}}} routine takes a CoordTransform object as a parameter, whereas the {{{transform_to}}} routine takes a SpatialReference object.  The {{{transform_to}}} "function requires internal creation and initialization of [a CoordTransform] object [and] it is significantly more expensive to use this function to transform many geometries than it is to create the [CoordTransform object] in advance, and call transform() with that transformation. This function exists primarily for convenience when only transforming a single geometry." 
    8486 
    8587= Example =