[postgis-users] Does ST_AsText truncate or round

[Håvard Tveite]

ST_GeomFromText(ST_AsText(geom)) != geom

sounds like a bug to me (ignoring the SRS).

Håvard

Paul Ramsey wrote:
> It all falls down into this function:
> 
> write_double(double val){
>         ensure(32);
>         if (lwgi)
>                 sprintf(out_pos,"%.8g",val);
>         else
>                 sprintf(out_pos,"%.15g",val);
>         to_end();
> }
> 
> 
> 
> On Fri, May 16, 2008 at 3:23 AM, Paragon Corporation <lr at pcorp.us> wrote:
>> Slight clarification about what I am trying to solve.
>>
>> After edits I am coming back with lines that used to be intersecting no
>> longer intersecting and that still have the same AsText representation.
>>
>> My hope is to reduce the precision of my geometry in the database so the
>> edits don't break the topology of my lines by doing something like this
>>
>>
>> Update sometable
>>        SET the_geom = ST_SetSRID(ST_AsText(the_geom), mysrid)
>>
>>
>> But I fear that if AsText is doing a rounding rather than a truncation, that
>> I run the risk of breaking things that used to intersect.  I am more
>> concerned about under intersecting than over intersecting.  Although I
>> probably haven't thought this out enough so maybe it's a non-issue.
>>
>> Thanks,
>> Regina
>>
>>
>>
>> -----Original Message-----
>> From: postgis-users-bounces at postgis.refractions.net
>> [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Paragon
>> Corporation
>> Sent: Friday, May 16, 2008 12:01 AM
>> To: 'PostGIS Users Discussion'
>> Subject: [postgis-users] Does ST_AsText truncate or round
>>
>> Hopefully this is a simple question.  I know that ST_AsText returns a
>> geometry that is not necessarily as prescise as what is actually stored in
>> the geometry field.  I have an editor that relies on WKT representation.
>>
>> Anyrate just wanted to know if the ST_AsText does a rounding of the points
>> or it does a truncation of the points.  Also would be nice to know if I
>> could control the precision of this since I will need to truncate my actual
>> geometry accordingly so that both are in agreement.
>>
>> Thanks,
>> Regina
>>
>>
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