Spatial Solutions Architect and Database Expert
I was asked the other day: In thinning the data we sometimes end up with collection features (2004 gtype), and I need to pull out the relevant geometry type (usually polygon) from the collection, because of course SDE is not happy with 2004 gtypes. I have covered this before, but often people email me askingRead More
Often I have need to know if the linestrings describing an sdo_geometry line or polygon object contain 3-point arc segments or elements. If a linestring or polygon is described by, or contains, 3-point circular arc elements when: Its sdo_interpretation field in the sdo_elem_info array will contain the values 2 or 4 Or its sdo_etype isRead More
Recently, I had cause to look at the implementation of the OGC/SQLMM Geometry_Columns and Spatial_Ref_Sys metadata views in Oracle. ISO/TC 211, 6.2 Architecture � SQL implementation using Geometry Types, 6.2.1 Overview says: “This standard defines a schema for the management of feature table, Geometry, and Spatial Reference System information in an SQL-implementation with a GeometryRead More
I gave a rather manic presentation (Open Source, Oracle and PostGIS) at the FOSS4G 2009 Conference at Darling Harbour in Sydney, Australia, on Thursday October 22nd. The presentation was a little risqué at times (anyone offended please accept my apologies: I seem to become a different person when I present) and, I suspect, its messageRead More
I received this email today from someone in Europe. Now I’m into XML/GML and I’ve worked out a mechanism to convert daily mutations into XML, with a GML tag. The reverse mechanism also works: convert the XML back to relational form. Problem is however that I’ve build it in Oracle 11g. When I tried @work,Read More
Ever needed to extract a textual description of all geometry types in a single geometry/geography in SQL Server 2008 inluding all sub-elements? Recently I had cause to do so and created the following function that implements this need. Now let’s test it against a selection of all possible geometry types I hope this function isRead More
I demonstrated in this article the usefulness of having a vectorising function in one’s spatial database kitbag (there are GetVector functions in my CENTROID and GEOM packages – in particular the GetVector function is vital to the implementation of the algorithm in my CENTROID.SDO_CENTROID function). So, I have also added one to my SQL ServerRead More
Oracle has a polygon geometry type (non-standard) called an optimized rectangle. To define one all one has to do is supply it with the lower-left and upper-right coordinates. This is a much easier thing to do than having to supply 5 coordinates in anti-clockwise order. PostGIS also has a bunch of bounding box functions thatRead More
I have pointed out in another blog that the result of an STIntersection() between two polygon objects could result in an object that is not a polygon or multipolygon. Intersection GEOMETRYCOLLECTION (POLYGON ((100 200, 180 300, 100 300, 100 200)), LINESTRING (100 200, 100 75), POINT (100 0)) Note, the the result is a geometryRead More