last_point - ObjectVision/GeoDMS GitHub Wiki

Geometric functions last_point

The last_point function extracts the last point from each sequence (arc, polygon, or linestring).

last_point(sequences: E->Sequence<Point>) -> E->Point

Returns the last point of each sequence geometry. For:

• Arcs/linestrings: The endpoint of the line
• Polygons: The last vertex (which equals the first vertex for closed rings)
• Empty sequences: Returns undefined (null)

This is the counterpart to first_point.

Time complexity: O(n) where n is the number of sequences (constant time per sequence).

Memory efficient as it only accesses the last element of each sequence without loading entire geometries.

• Input must be a sequence type (arc, polygon, linestring)
• Result is undefined for empty sequences

unit<uint32> Roads: nrofrows = 100;
attribute<FPoint> geometry (poly, Roads);  // road linestrings

// Get start and end points of each road
attribute<FPoint> start_point (Roads) := first_point(geometry);
attribute<FPoint> end_point (Roads) := last_point(geometry);

// Road length from first to last point (simplified)
attribute<Float64> straight_distance (Roads) := dist(start_point, end_point);

• first_point - extracts first point
• sequence2points - extracts all points from sequences
• centroid - center of mass of geometry
• Geometric functions

5.0