[postgis-users] Converting WKT or WKB

[Abe Gillespie]

Thanks for the help, but I intend to keep my PostGIS data in it's 
native format.  Only at the instant I want to use the data inside 
ESRI's API do I need to do the conversion.

I'm trying to create a tool that allows read / write ability of PostGIS 
inside of ArcMap.  And yes I'm familiar with pgArc ... but it's 
incomplete, slow, and buggy.

-Abe

On Feb 6, 2005, at 1:38 PM, Brent Wood wrote:

>
> --- Abe Gillespie <agillesp at vt.edu> wrote:
>
>> Hello all.  I'm new to the list.
>>
>> I've just started using PostGIS, I'm one from the MapServer crowd.  
>> I'd
>> like to use PostGIS with some ESRI technologies and am hoping to find
>> an easy way to go from PostGIS objects to ESRI objects.
>
> As you are using PostGIS I'm assuming that you are just interested in 
> using
> vector data?
>
> There is a shp2pgsql program which turns a shpfile into a file of SQL 
> commands
> to load into PostGIS. The QGIS package has a plugin which allows you 
> to click
> on shapefiles and choose a PostGIS database to load them into. Also 
> the ogr2ogr
> program (part of the GDAL suite) converts between various vector 
> formats, and
> can convert to/from PostGIS tables, shape and Arc coverage (amongst 
> others).
>
> Then there is avce00 which works with e00 Arc export files, converting 
> then
> to/from coverages.
>
> So these are several Open Source packages which support shapefiles and 
> PostGIS,
> as well as a way to turn e00 & coverages into shapefiles.
>
> The Postgres native spatial data types are not compatible AFAIK with 
> PostGIS,
> nor are there any conversion tools. I think I have seen this issue 
> raised
> before, so trawling the list archives might find you something.
>
> Note that the shapefile spec necessarily loses some topology info, etc 
> from
> coverages, and that PostGIS does not really support topology, and only 
> features
> defined by coordinate pairs, so circles etc cannot be represented by a 
> point &
> radius, but must be renderedr into an arc of coords. Dynamic 
> segmentation &
> other capabilities can sort of be implemented with suitable table 
> structures,
> but depending on your Arc data you may lose something.
>
> I'm not expert in this area, but I believe geometries are stored as 
> binary, but
> can be extracted as WKT if required.
>
>
> Brent Wood
>
>
>>
>> My first idea is using Postgres native geometry types.  The .Net data
>> connector (Npgsql) has support for these built in types.  Are there 
>> any
>> PostGIS functions that will convert its types to Postgres geometry
>> types?  I imagine things working sort of like:
>>
>> string sql = "SELECT as_native_postgres_box(extent(the_geom)) FROM
>> shape_table";
>> NpgsqlCommand cmd = new NpgsqlCommand(sql, con);
>> NpgsqlBox box = (NpgsqlBox)cmd.ExecuteScalar();
>>
>> The second idea is to just use a third party library to do the parsing
>> for me.  I see there's a java one, but I'm looking for a .Net happy
>> library.
>>
>> Also, and this is OT from the subject, but how do you specify to
>> PostGIS whether the geometries are stored as WKT or WKB?  Mine are all
>> WKT and I'm curious in case down the road I want to use WKB.
>>
>> Thanks for any help.
>> -Abe
>>
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