Overlaying Polygons in SQL Server Spatial

Introduction The OGC operators for geometry processing only support two polygon inputs. Additionally the Microsoft aggregate operators only include geometry union processing geometry::UnionAggregate and not overlay processing etc. UnionAggregate returns for all input polygons as the single Union (see above) does. Concept: Resolving all overlapping areas, without dissolving boundaries, is called “planar enforcing”. Planar enforcementRead More

The Frontage Problem: Creating references from land parcel street frontage boundary to point in street

This article demonstrates the power of database-based spatial processing. The business requirement is to determine, dynamically, the side of a land parcel that faces the street (could be single 2 point straight line to something more complex), and then determine the clockface direction from either ends of the frontage or the middle, to a object in the roads reserve (eg telecommunications pit).

ST_Densify for Object PLSQL

The Java Topology Suite (JTS) has a linestring densifier function that is available in my Spatial Companion for Oracle (SC4O) solution. See here for documentation. For those who aren’t able to install SC4O (some DBAs don’t like it), there was a PL/SQL function in my the old GEOM Package implemetation on this website that allowsRead More

STFlipVectors: Normalize direction of linestring vectors

In the past I have found use for the ability to “flip” vectors in a polygon in order to provide an independent check on the topological integrity of planar enforced polygons. What I mean by topological integrity is that there are no gaps or overlaps between adjacent polygons. A simple method for doing this reliesRead More

STVectorize: Break Linestring/Polygon elements into 2 point vectors (or 3 point circular curves)

I demonstrated in this article the usefulness of having a vectorising function in one’s spatial database kitbag (there are Vectorize functions in my CENTROID and GEOM packages – in particular the Vectorize function is vital to the implementation of the algorithm in my CENTROID.ST_CENTROID function). So, I have also added one to my SQL ServerRead More

Extracting Inner Rings Changed Ordinate Ordering: A Trap For Players Who Don’t Read Documentation!

In Developing Some Ideas For The Compression/Decompression Of Sdo_Geometry Objects, I Had Cause To Create Two PL/SQL Functions called Geocompress and Geodecompress. I Have Not Done This For A While And Slapped Myself When I Ran Into something I Should Have Known Would Arise, as I have seen it before, and because it is documentedRead More

How far inside, is inside? Measuring actual distance.

One issue that confuses a lot of spatial database practitioners is that the result of measuring the distance between a geometry object inside a polygon and that polygon’s boundary is zero (0). Here is an example. This looks like: Standard distance determination shows the problem: Here is a trick that will allow for the calculationRead More