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<P><FONT SIZE=2>Regina --<BR>
<BR>
I think the lwgi is testing for whether the installation has the "light-weight" postGIS stuff -- fewer decimal places resulting (%f and %g are formatting options in a print statememnt for decimal representation -- so 8 or 15 places respectively.<BR>
<BR>
(I think -- never crawled into the guts of postGIS' C code).<BR>
<BR>
(Sorry for top posting and the disclaimer -- only one per thread, I promise!)<BR>
<BR>
Greg Williamson<BR>
Senior DBA<BR>
DigitalGlobe<BR>
<BR>
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-----Original Message-----<BR>
From: postgis-users-bounces@postgis.refractions.net on behalf of Obe, Regina<BR>
Sent: Fri 5/16/2008 12:33 PM<BR>
To: PostGIS Users Discussion<BR>
Subject: RE: [postgis-users] Does ST_AsText truncate or round<BR>
<BR>
Paul,<BR>
<BR>
I think you mistook me for a C programmer if you actually thought I<BR>
could figure out my answer from this snippet of code :)<BR>
<BR>
First I can't remember what g means. I remember seeing fs and gs<BR>
somewhere before so I can only assume that f means round and g means<BR>
truncate?<BR>
<BR>
Secondly what does lwgi stand-for - I can only guess it means<BR>
light-weight geom or something along that - so does that mean that as<BR>
far as I'm concerned - .8g is the loop I'm interested in? Do we even<BR>
use non-light weight anymore?<BR>
<BR>
Thanks,<BR>
Regina<BR>
<BR>
-----Original Message-----<BR>
From: postgis-users-bounces@postgis.refractions.net<BR>
[<A HREF="mailto:postgis-users-bounces@postgis.refractions.net">mailto:postgis-users-bounces@postgis.refractions.net</A>] On Behalf Of Paul<BR>
Ramsey<BR>
Sent: Friday, May 16, 2008 10:39 AM<BR>
To: PostGIS Users Discussion<BR>
Subject: Re: [postgis-users] Does ST_AsText truncate or round<BR>
<BR>
It all falls down into this function:<BR>
<BR>
write_double(double val){<BR>
ensure(32);<BR>
if (lwgi)<BR>
sprintf(out_pos,"%.8g",val);<BR>
else<BR>
sprintf(out_pos,"%.15g",val);<BR>
to_end();<BR>
}<BR>
<BR>
<BR>
<BR>
On Fri, May 16, 2008 at 3:23 AM, Paragon Corporation <lr@pcorp.us><BR>
wrote:<BR>
> Slight clarification about what I am trying to solve.<BR>
><BR>
> After edits I am coming back with lines that used to be intersecting<BR>
no<BR>
> longer intersecting and that still have the same AsText<BR>
representation.<BR>
><BR>
> My hope is to reduce the precision of my geometry in the database so<BR>
the<BR>
> edits don't break the topology of my lines by doing something like<BR>
this<BR>
><BR>
><BR>
> Update sometable<BR>
> SET the_geom = ST_SetSRID(ST_AsText(the_geom), mysrid)<BR>
><BR>
><BR>
> But I fear that if AsText is doing a rounding rather than a<BR>
truncation, that<BR>
> I run the risk of breaking things that used to intersect. I am more<BR>
> concerned about under intersecting than over intersecting. Although I<BR>
> probably haven't thought this out enough so maybe it's a non-issue.<BR>
><BR>
> Thanks,<BR>
> Regina<BR>
><BR>
><BR>
><BR>
> -----Original Message-----<BR>
> From: postgis-users-bounces@postgis.refractions.net<BR>
> [<A HREF="mailto:postgis-users-bounces@postgis.refractions.net">mailto:postgis-users-bounces@postgis.refractions.net</A>] On Behalf Of<BR>
Paragon<BR>
> Corporation<BR>
> Sent: Friday, May 16, 2008 12:01 AM<BR>
> To: 'PostGIS Users Discussion'<BR>
> Subject: [postgis-users] Does ST_AsText truncate or round<BR>
><BR>
> Hopefully this is a simple question. I know that ST_AsText returns a<BR>
> geometry that is not necessarily as prescise as what is actually<BR>
stored in<BR>
> the geometry field. I have an editor that relies on WKT<BR>
representation.<BR>
><BR>
> Anyrate just wanted to know if the ST_AsText does a rounding of the<BR>
points<BR>
> or it does a truncation of the points. Also would be nice to know if<BR>
I<BR>
> could control the precision of this since I will need to truncate my<BR>
actual<BR>
> geometry accordingly so that both are in agreement.<BR>
><BR>
> Thanks,<BR>
> Regina<BR>
><BR>
><BR>
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