I'm trying to extrapolate from a line segment to find a point on the line but a 3rd of the way 'back', i.e. trying to find point
new, given points
Given a line, I can interpolate it to get a position at any particular percentage along it:
=# select st_line_interpolate_point( st_makeline('0101000020E6100000300DC347C49418C03EE8D9ACFAA44A40', '0101000020E6100000FB743C66A03218C0CDCCCCCCCC7C4A40'), 0.333); 0101000020E6100000ED45B41D537718C069C6A2E9EC984A40
I tried entering a negative number to find a point along the line in the opposite direction, but that fails as the interpolation argument has to be in the range [0, 1]
I thought about first scaling the line, but that doesn't use the centre of the line as the origin, so is useless for my purposes.