On 2014-09-30 17:08, Even Rouault wrote:
Le mardi 30 septembre 2014 20:20:14, Andre Vautour a écrit :
Hi all,
I am trying to use a geometry binary predicate (ST_Intersects) in
ExecuteSQL() with the SQLite dialect and keep getting back an
"ST_Intersect function does not exist" error back from SQLite.
GDAL is built with SpatiaLite (HAVE_SPATIALITE is defined), but I
believe the problem is that SpatiaLite is built without GEOS in our
case, so those predicate functions end-up not being available in
SpatiaLite. The end result is that OGRSQLiteRegisterSQLFunctions does
not add the OGR-based predicate functions as SpatiaLite is present, but
SpatiaLite does not contain the predicate functions.
I would build SpatiaLite with GEOS support, but unfortunately its LGPL
licensing is too restrictive for our application. So, would it make
sense to change the logic in OGRSQLiteRegisterSQLFunctions to account
for the case of SpatiaLite being built without GEOS?
Andre,
That makes sense. I guess that can only be checked at runtime though, probably
by issuing a ST_Intersects() and checking the error code.
I'd note that the spatial predicates in OGR geometry are also based on GEOS.
Except OGRGeometry::Intersects() that has a simplified implementation based on
bounding box intersection when GEOS is not available.
Some time ago, I had a look at boost geometry (
http://www.boost.org/doc/libs/1_56_0/libs/geometry/doc/html/index.html ). That
could be used as an alternative backend to GEOS for most predicates and
functions returning geometries, and the boost licence is a modified X/MIT.
In that case, I might lean towards implementing the binary predicates as
SQLite functions at our level given that we have a proprietary
implementation of ISO 19107.
In order to do so, I'd need to have a way to add functions to the
created sqlite3 object. Assuming we cache the sqlite data source between
SQL executions, one option would be to enable the loadable extensions on
the created sqlite3 object like is done in
sqlite\test_load_virtual_ogr.c using sqlite3_enable_load_extension(). I
could then call ExcuteSQL() with "SELECT load_extension(...)". Another
option would be to expose a callback that would allow an application to
add functions to an SQLite database when it is created, that is, expose
something similar to OGR2SQLITEModule::SetHandleSQLFunctions().
Yet another option would be to allow for an extension point by
introducing something like an OverlayStrategy and having the default be
the GEOSOverlayStrategy. That would allow for the boost::geometry
extension point you were talking about, and allow applications that have
their own geometry library like us to use their in house implementation
for predicates and overlays.
Would you guys be willing to take one of those options?
Thanks again,
André
Even
--
*André Vautour*, B.Sc.
Application Developer
CARIS <http://www.caris.com>
115 Waggoners Lane
Fredericton, New Brunswick
Canada E3B 2L4
Tel: +1.506.458.8533 Fax: +1.506.459.3849
www.caris.com <http://www.caris.com>
*Connect with CARIS*
Twitter <http://www.twitter.com/CARIS_GIS> LinkedIn
<http://www.linkedin.com/groups?mostPopular=&gid=3217878> FaceBook
<http://www.facebook.com/pages/CARIS-The-Marine-GIS-Experts/123907500987669?v=app_4949752878>
YouTube <http://www.youtube.com/user/CARISGIS>
Download your free copy of CARIS Easy View today!
www.caris.com/easyview <http://www.caris.com/easyview>
_________________________________________________________________________
This email and any files transmitted with it are confidential and
intended only for the addressee(s). If you are not the intended
recipient(s) please notify us by email reply. You should not use,
disclose, distribute or copy this communication if received in error.
Any views or opinions expressed in this email are solely those of the
author and do not necessarily represent those of the company. No binding
contract will result from this email until such time as a written
document is signed on behalf of the company.
_______________________________________________
gdal-dev mailing list
[email protected]
http://lists.osgeo.org/mailman/listinfo/gdal-dev
