[postgis-users] C++ and Postgis

[Paul Ramsey]

If it's just points, do it all on the server side, skip encoding formats

select st_x(pt) as x, st_y(pt) as y from mytable where myclause();

P.

On Mon, Nov 23, 2009 at 2:43 PM, Pedro Doria Meunier
<pdoria at netmadeira.com> wrote:
> Thank you Paul and John for your ideas. :)
>
> Actually what I'm trying to do is to decode simple POINT geoms...
>
> This is what I've done in PHP (using the astext() approach)
>
>      // extract the geometry
>      $geometry = str_replace("POINT(","", $loc);
>      $geometry = str_replace(")","",$geometry);
>      $coordinate = explode(" ",$geometry);
>      $lon=$coordinate[0];
>      $lat=$coordinate[1];
>
> Now this was for the web interface... ( the user can wait another 100ms or
> so ... :] )
> As far as a server solution is concerned this *is* a time-consuming
> procedure... especially so when you've got *thousands* of connections per
> minute...
>
> Furthermore, I'm developing the "beast" in Qt4 and - *ahem* - had never
> needed to use libpq so I'm a bit lost here... :)
>
> Could someone be so kind as to point to a code example (outside using
> astext() method) ? :]
>
> P.S. @John - found this to be interesting as I could store it in QByteArray
> and go from there... ;) -- the real question here is: how to interpret the
> byte array?
>
> BR,
> Pedro.
>
>
> On 11/23/2009 09:50 PM, Paul Ramsey wrote:
>>
>> That depends entirely on what you're planning to do with them once you
>> get them. You'll probably want to serialize them into a known form so
>> you can use them on the client side. ST_AsText() is one, very heavy,
>> option. Mapserver, to take an example, uses
>> encode(ST_AsBinary(ST_Force2D(geom)), 'hex'), so what goes over the
>> wire is hex strings, but those are easy to turn into binary arrays, in
>> WKB format, suitable for reading by a number of C++ libraries (like
>> OGR or GEOG or etc).
>>
>> Best,
>>
>> P.
>>
>> On Mon, Nov 23, 2009 at 1:19 PM, Pedro Doria Meunier
>> <pdoria at netmadeira.com>  wrote:
>>
>>>
>>> Hi All,
>>>
>>> First off sorry for cross-posting. I'm hoping for a bigger audience... :]
>>>
>>> As for my question:
>>>
>>> How does one deal with Postgis geom fields in C++ ?
>>> Google hasn't offered much help so far.
>>>
>>> I know I can make a "SELECT astext(my_geom) FROM my_table" and after
>>> parsing
>>> the resulting text.
>>> This seems a bit awkward and time-consuming...
>>>
>>> Is there a better way to deal with it?
>>>
>>> Already thankful for any ideas,
>>> BR,
>>> Pedro.
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>>>
>>>
>>
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