[postgis-users] simplify

[Stephen Crawford]

OK, I lied about the "last question for today" thing:

I understand about simplifying on decimal degrees data, but I really want to
keep the data in WGS84 and then reproject in Geoserver as needed.  To
simplify, should I first Transform() to, say, Mercator, then Simplify(),
then transform back to WGS84? That seems like ti would be the same problem.
And most other projections are not appropriate for such a large area....my
data are for the entire Western Hemisphere.

Thanks,
Steve



-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Paul
Ramsey
Sent: Thursday, March 01, 2007 5:09 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] simplify

The units for Simplify() are the units of the data, so yes, if you
Simplify() decimal degrees data, you'll want to supply a decimal degrees
tolerance.

That said, DO NOT use Simplify() on decimal degrees data unless you live on
the equator.  The difference in scale horizontally and vertically in more
northerly areas will result in "odd" simplifications when in decimal
degrees.

Paul

Stephen Crawford wrote:
> One last question and I'll leave you all alone for the day :)
> 
> If I want to generalize my data, I should simplify()?  So if the data 
> are in decimal degrees, then is the tolerance decimal degrees?  
> Something like this?
> 
> CREATE TABLE accipiter AS SELECT 
> 	gid,engl_name,sci_name,origin,Simplify(the_geom,0.01) as the_geom 
> FROM all_species WHERE family='Accipitridae';

-- 

   Paul Ramsey
   Refractions Research
   http://www.refractions.net
   pramsey at refractions.net
   Phone: 250-383-3022
   Cell: 250-885-0632
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