[postgis-users] Select Point near Polyline Postgis

[anhtin]

hi Rodrigo 
this  my column the_geom is type "MULTILINESTRING"
and all geometry data on this table  is type = "MULTILINESTRING"
when i run this script:
SELECT * ,
line_interpolate_point(the_geom,line_locate_point(the_geom,PointFromText('POINT(517651
2121421)', 42102)))
FROM mainroad WHERE (GeometryType(the_geom) = 'LINESTRING')
 ORDER BY Distance(the_geom,PointFromText('POINT(517651 2121421)', 42102))
LIMIT 1

it not error, however it has not result because geometry data is type =
"MULTILINESTRING"

but when i add a condition is:
WHERE (GeometryType(the_geom) = 'LINESTRING') or (GeometryType(the_geom) =
'MULTILINESTRING')
 it have exception error:

ERROR: line_locate_point: 1st arg isnt a line
SQL state: XX000

I think this script error because the condition (GeometryType(the_geom) =
'MULTILINESTRING')

How could i do? Because my all geometry data is MULTILINESTRING  type. 
Could i convert my geometry data to orther data type ("LINESTRING").
But i think it not good if i convered to orther type.

this is my Data MainRoad. Can u try to use it. And u could show me the good
a way :).
http://www.nabble.com/file/p11151446/data%2Btype%2BMainRoad.rar
data+type+MainRoad.rar 







Rodrigo Martín LÓPEZ GREGORIO-3 wrote:
> 
> I think the problem obviously is that some geometries in your table are
> not
> linestrings or multilinestrings. You can check it doing:
> 
> SELECT GeometryType(the_geom) FROM mainroad WHERE GeometryType(the_geom)
> !=
> 'LINESTRING'
> 
> Then you will find wich Geometries are not linestring and those are the
> ones
> that are giving you some problems. You must take a look at that geometries
> and choose what to do with them.
> 
> As a temporary sollution I think you can add a condition to your query
> that
> only takes into account for the result the geometries that are LINESTRING.
> So your query will look something like this:
> 
> SELECT * ,
> line_interpolate_point(the_geom,line_locate_point(the_geom,PointFromText('POINT(5176512121421)',
> 42102))) FROM
> mainroad WHERE GeometryType(the_geom) = 'LINESTRING' ORDER BY
> Distance(the_geom,PointFromText('POINT(517651 2121421)', 42102)) LIMIT 1
> 
> Maybe you can also consider the 'MULTILINESTRING' geometries; the
> line_interpolate_point should work also with that type of geometry. So the
> condition will be:
> 
> WHERE (GeometryType(the_geom) = 'LINESTRING') or (GeometryType(the_geom) =
> 'MULTILINESTRING')
> 
> I never used any SRID in my querys but I don't think that can be a problem
> at all.
> 
> Rodrigo.
> 
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> postgis-users at postgis.refractions.net
> http://postgis.refractions.net/mailman/listinfo/postgis-users
> 
> 

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