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All Blog Articles, Data Models and Free Source Code by Simon Greener, The SpatialDB Advisor is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

Drawing a layer in GeoRaptor: Simple Gotchas!

Wednesday December 19 2012 at 09:34

A question from a user:

It seems as though the system calculates extents that are HUGELY larger than the actual geometry. I have found by putting a label on it that you sill see a tiny blob then using the windowed zoom I can then start showing the links and eventual remove the label. Idea’s ?

From this it appears that:

1. Hist data must be geodetic/geographic, or
2. The diminfo for the table/column is set to the widest possible extent ie -180..180 and -90..90 and not something smaller and closer to the extent of your data. (While the documentation says to do this, most practitioners do not – they set the diminfo to the extent of the actual data. It makes no different to Oracle but a lot of software like GR, QGIS etc that use the diminfo as the MBR of the layer.)

When one first adds a table/column to the map view, GR checks if the data is planar. If it is planar the actual extent of the data to extracted from the header record of the rtree index (stored in the mdsys index metadata). But this data is not useable for geodetic/geographic data so GR has to go to the user_sdo_geom_metadata entry to get the diminfo values.

In addition, if the data is not point data then GR automatically implements the sdo_filter pixel filtering. This can be turned off in Preferences.

Finally, to create a decent map extent for the layer, right mouse click, properties for the layer. Then tick the box marked “Recalculate MBR (next draw)”. This makes GR compute an MBR that covers only the data returned via the next draw query.

regards
Simon

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