Contents
How is the centroid computed for a polygon?
For [ MULTI] POLYGON s, the centroid is computed in terms of area. If an empty geometry is supplied, an empty GEOMETRYCOLLECTION is returned. If NULL is supplied, NULL is returned.
What kind of join is used in PostGIS?
By default, we are using an INNER JOIN, but there are four other types of joins. For further information see the join_type definition in the PostgreSQL documentation. We can also use distance tests as a join key, to create summarized “all items within a radius” queries.
How are spatial joins used in GIS analysis?
Much of what we think of as “standard GIS analysis” can be expressed as spatial joins. In the previous section, we explored spatial relationships using a two-step process: first we extracted a subway station point for ‘Broad St’; then, we used that point to ask further questions such as “what neighborhood is the ‘Broad St’ station in?”
Is the centroid equal to the set of component geometries?
The centroid is equal to the centroid of the set of component Geometries of highest dimension (since the lower-dimension geometries contribute zero “weight” to the centroid).
For [ MULTI] POLYGON s, the centroid is computed in terms of area. If an empty geometry is supplied, an empty GEOMETRYCOLLECTION is returned. If NULL is supplied, NULL is returned. If CIRCULARSTRING or COMPOUNDCURVE are supplied, they are converted to linestring wtih CurveToLine first, then same than for LINESTRING
When is the result equal to the centroid?
For mixed-dimension input, the result is equal to the centroid of the component Geometries of highest dimension (since the lower-dimension geometries contribute zero “weight” to the centroid). New in 2.3.0 : support CIRCULARSTRING and COMPOUNDCURVE (using CurveToLine)
Is the centroid of a circle equal to the curvetoline?
If CIRCULARSTRING or COMPOUNDCURVE are supplied, they are converted to linestring wtih CurveToLine first, then same than for LINESTRING For mixed-dimension input, the result is equal to the centroid of the component Geometries of highest dimension (since the lower-dimension geometries contribute zero “weight” to the centroid).