id,summary,reporter,owner,description,type,status,priority,milestone,component,version,resolution,keywords,cc
272,ST_LineCrossingDirection should be negatively symmetric,robe,pramsey,"I propose that to minimize on confusion

It should hold true that: 

 ST_LineCrossingDirection(a,b) = - ST_LineCrossingDirection(b,a)

--- below is a relevant excerpt from the previous crashing ticket  -

Regina

{{{
But I think there is still a problem.

In our documentation -- We still have this example that doesn't behave right

SELECT ST_LineCrossingDirection(foo.line1, foo.line2) As l1_cross_l2 ,

    ST_LineCrossingDirection(foo.line2, foo.line1) As l2_cross_l1

FROM (SELECT

    ST_GeomFromText('LINESTRING(25 169,89 114,40 70,86 43)') As line1, ST_GeomFromText('LINESTRING(2.99 90.16,71 74,20 140,171 154)') As line2 ) As foo;

(gives me -2, 0)

http://www.postgis.org/documentation/manual-svn/ST_LineCrossingDirection.html 
}}}

Mark's Response

{{{
Yeah; I see exactly the same answers. Unfortunately though, I can't make much sense of the integer constants in the manual to work out what the function *should* actually be doing. Can anyone explain this in more detail? For example, do the LEFT/RIGHT parts refer to spatial position or the order of the input parameters?

ATB,

Mark.

}}}
",defect,closed,medium,PostGIS 1.4.1,postgis,1.4.X,fixed,,