[postgis-users] issue with pgsql2shp

[John Cole]

Strk,
  Thanks for the reply.  On issue 1) I am using the query and getting the
error about the geometry types (unless you are talking about using a
sub-query).

  With SnapToGrid in issue 2) will it eliminate any points that snap to the
same point?

  On issue 3) the Segmentize returns [multi]polygons according to the
documentation, will it also work on lines and return those as well?

Thanks,

John

-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of
strk at refractions.net
Sent: Monday, June 05, 2006 8:56 AM
To: 'PostGIS Users Discussion'
Subject: Re: [postgis-users] issue with pgsql2shp

On Fri, Jun 02, 2006 at 09:05:46AM -0500, John Cole wrote:
> I'm trying to create shapefiles from tiger data inside our postgis
database
> with pgsql2shp.  Since these shapefiles are for rendering with mapserver
> only, I'd like to pre-process these so they are optimal for rendering at
> certain scales and maximize mapserver performance.  I'm using "1.0
> USE_GEOS=1 USE_PROJ=1 USE_STATS=1" of PostGIS.
> 
> Here are some issues I've run into:
> 
> 1)  If I give pgsql2shp a query like "select the_geom from tgr_roads where
> cfcc like 'A1%' or cfcc like 'A2%'", I get the following error; ERROR:
> Cannot determine geometry type (empty table).  I found a mail list message
> from 2003 about adding a -t switch to specify the geometry type, but that
> doesn't appear in this version.  I'd like to do this without creating
> temporary tables.

You can use a query instead of a tablename.

> 2)  I'd like to make reduced resolution shapefiles for certain scales (for
> example, at 1M scale, no feature should be shorter than 250 meters, the
size
> of one pixel on the map).  Does the simplify() function do this?  I have
the
> following query, which I think does this, but I get the same error as in
1)
> above.

I suggest SnapToGrid() for pixel-based precision reduction.
Use a grid's cell size equal to your pixel size.

> select transform(simplify(transform(collect(the_geom),32616),250), 4326)
as
> the_geom from tgr_roads where cfcc like 'A1%' or cfcc like 'A2%' group by
> hwy_num, rd_name
> 
> 3)  I don't see the equivalent densify() ArcInfo function in PostGIS, is
> there one?  When creating reduced resolution shapes, I like to densify
they
> line to 1-10 meters and then reduce the resolution to 250 meters to ensure
> that the original shape of the file is retained.

Could this be segmentize() ?

--strk;
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