Hi everyone, I'm looking for someone with experience with GiST and PostgreSQL to offer some advice on the following problem:
I'm currently looking at improving the R-Tree implementation of PostGIS (http://postgis.refractions.net) by consolidating the indexable and non-indexable operators so that they use the same functions. Each geometry in the database is indexed by its bounding box as normal. However, each database column also has a spatial reference system identifier (SRID) that specifies the coordinate system the geometry is in. What should happen is that given two geometries or bounding boxes, an error should be generated whenever the SRIDs do not match. The problem I am wrestling with at the moment is that the indexable operators do not check the SRID between two geometries; this is because a standard PostgreSQL BOX is used to specify the bounding boxes in the index and so by extracting the key from the GISTENTRY structure, it is impossible to determine whether the SRIDs match because the SRID is stored in the geometry and not the index key. The current line of thinking is to modify the index to use a structure like below as the index key: typedef struct BOX2D { double LLB; // Lower left bottom double URT; // Upper right top long srid; // Spatial ref sys identifier } However we know that for a given column (and index) the SRID will be the same so it seems pointless to store the SRID in the index itself as it is redundant information. The problem is therefore how is the best method to store the SRID for a given column while keeping the index as small as possible? The only thing I can think of is to use the Relation, Page and Offset pointers in the GISTENTRY structure to somehow return a reference to the geometry and return the SRID as part of the Decompress() function for leaf nodes. But this seems like a lot of extra work, even if it only has to be done for leaf nodes, and I don't have a clue which routines I would need to do this. Does anyone have a better idea as to how this could be done, perhaps some way of storing/retrieving metadata about an index through GiST? Cheers, Mark. --- Mark Cave-Ayland Webbased Ltd. Tamar Science Park Derriford Plymouth PL6 8BX England Tel: +44 (0)1752 764445 Fax: +44 (0)1752 764446 This email and any attachments are confidential to the intended recipient and may also be privileged. If you are not the intended recipient please delete it from your system and notify the sender. You should not copy it or use it for any purpose nor disclose or distribute its contents to any other person. ---------------------------(end of broadcast)--------------------------- TIP 3: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly