[Mapserver-users] GEOS intersection problem

[songzh at cs.orst.edu]

When I performed the intersection between a MULTILINESTRING and a POLYGON, the
generated MULTILINESTRING shot off a line which went outside the images
extents. The details are as the following:   

  1) The version of GEOS is downloaded from: [2003//11/06]geos-1.0.0.tar.gz on
http://geos.refraction.net
     It's the latest version I can find. 
  2) The intersection geometry objects are as the following. 

geom_base (it has three single lines with a common jointed point): 
  "SRID=6010;MULTILINESTRING((602797 1045929,602897 1045629),(602897
1045629,602997 1045929),(602897 1045629,602897 1045529,602897 1045599,602897
1045439,602897 1045429))"

geom_py (a rectangle):
  "SRID=6010;POLYGON((602797 1045829,602997 1045829,602997 1045529,602797
1045529,602797 1045829))"

  3) After the SQL statement "select intersection(geom_base, geom_py) from
intersect_test" was issued, the intersected geometry object was:

geom_intersect ( a multilinestring):
  "SRID=6010;MULTILINESTRING((602830.333333333 1045829,602897 1045629),(602897
1045629,602963.666666667 1045829),(602897 1045629,602897 1045599),(602897
1045599,2.30261934254173e-269 1.20137436645991e-301))"
     

We can see that one of the generated multiline string has a point "
2.30261934254173e-269 1.20137436645991e-301 " which is actually (0,0). It shows
that one of the result line string links to the point (0, 0), which caused the
line going out the image range.
I want to know if anybody has any idea about this. How to avoid it?

Thanks a lot!


Yours,
Zhigang Song