Contents
How to get the concave hull of a polygon?
It is not an aggregate function, but can be used with ST_Collect or ST_Union to get the concave hull of a set of points/linestring/polygons (e.g. ST_ConcaveHull (ST_Collect (somepointfield), 0.80). It is slower to compute than the convex hull but generally has a smaller result area and represents a more natural bounds of the input geometry.
What is the result of convexhull tool in QGIS?
I use Convexhull tool in QGIS and there are result value : AREA = 0.0017494390 PERIMETER = 0.1725495172 I thought the result was strange. So, I took a rough estimate of the points through the
What is the target percent of concave Hull?
The target_percent is the target percent of area of convex hull the PostGIS solution will try to approach before giving up or exiting. One can think of the concave hull as the geometry you get by vacuum sealing a set of geometries.
When to use St _ concavehull and St _ Union?
It is usually used with MULTI and Geometry Collections. It is not an aggregate function, but can be used with ST_Collect or ST_Union to get the concave hull of a set of points/linestring/polygons (e.g. ST_ConcaveHull (ST_Collect (somepointfield), 0.80).
How are polygons with holes set in boost?
Sets the polygon holes the iterator range of hole polygons. These polygons in the input range may be either polygon_data or polygon_with_holes_data or any type that provides begin and end member functions to iterate over point_data .
Can a mutable polygon have holes in it?
A mutable polygon_with_holes must also be able to set its geometry based on an interator range over polygon holes. There is no convention of winding of holes enforced within the library. Below is shown the default polygon with holes traits.
Can a polygon with a hole be a iterator?
The semantic of a polygon_with_holes is a polygon that it can provide iterators over holes that are also polygon. A mutable polygon_with_holes must also be able to set its geometry based on an interator range over polygon holes. There is no convention of winding of holes enforced within the library.
Is the convex hull of a point an aggregate function?
The convex hull of one or more identical points is a Point. It is usually used with Multi* and GeometryCollections. It is not an aggregate function. To compute the convex hull of a set of geometries, use ST_Collect to aggregate them. One can think of the convex hull as the geometry obtained by wrapping an elastic band around a set of geometries.
Is the target percent of area of convex hull true?
The result is a single polygon, line or point. It will not contain holes unless the optional allow_holes argument is specified as true. The target_percent is the target percent of area of convex hull the PostGIS solution will try to approach before giving up or exiting.
How to calculate the convex hull of two collinear points?
The convex hull of two or more collinear points is a two-point LineString. The convex hull of one or more identical points is a Point. It is usually used with Multi* and GeometryCollections. It is not an aggregate function. To compute the convex hull of a set of geometries, use ST_Collect to aggregate them.
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