I have a postgis table of simple linestrings, each one is a straight line with just two points. I want to select every linestring, but extended from both sides by 1 meter. So i have lines, that are longer by 2 meters. How can this be done?
I seems very similar to post "postgis, extrapolate a line". If I avoid repetition of cited post, I think you just need to extrapolate beyond your extreme points. In a query you get something like this should work:
SELECT ST_MakeLine(ST_TRANSLATE(a, sin(az1) * len, cos(az1) * len),ST_TRANSLATE(b,sin(az2) * len, cos(az2) * len)) FROM ( SELECT a, b, ST_Azimuth(a,b) AS az1, ST_Azimuth(b, a) AS az2, ST_Distance(a,b) + 1 AS len FROM ( SELECT ST_StartPoint(the_geom) AS a, ST_EndPoint(the_geom) AS b FROM ST_MakeLine(ST_MakePoint(1,2), ST_MakePoint(3,4)) AS the_geom ) AS sub ) AS sub2