[postgis-users] Left of/Right of test

[Denis Rouzaud]

Oops, here is the complete code:

pointGeom << ST_Intersection( ST_MakeLine(
              ST_MakePoint(ST_XMin(lineGeom), ST_Y(pointGeom)),
              ST_MakePoint(ST_XMax(lineGeom), ST_Y(pointGeom))
                           ), lineGeom
                                                                 )



On 07/23/2013 04:31 PM, Denis Rouzaud wrote:
> Hi Andreas,
>
> Do you mean you want to test to a segment?
>
> Because, I can't see a true answer for a line.
>
> If you want to do test to a segment, it should do the job to test if 
> the intersection with the horizontal line (dy=0) over your point and 
> your input line is on the left/right to your point.
>
> So, maybe test:
>
> pointGeom << ST_Intersection( ST_MakeLine(
>             ST_MakePoint(ST_XMin(lineGeom), ST_Y(pointGeom)),
>             ST_MakePoint(ST_XMax(lineGeom), ST_Y(pointGeom))
>                                                                )
>
> You have to handle the case where your segment is horizontal, but then 
> a simple test with ST_Xmin/max should be enough.
>
> Cheers,
>
> Denis
>
> On 07/23/2013 03:54 PM, Andreas Neumann wrote:
>> Hi,
>>
>> I want to test a point if it is left-of or right-of a given LINESTRING.
>> I found the << >> and &< &> but they do not behave like I expected.
>>
>> Perhaps it is because they only test on the bounding box level and not
>> on the real geometry?
>>
>> Is there a left/right of test available on the geometry instead of the
>> bounding box?
>>
>> Thank you,
>> Andreas
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>