[rttopo-dev] Help in using the library

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[rttopo-dev] Help in using the library

Roberto Ribeiro
Hello list,

I was directed here by the nice folks at the PostGIS-devel list. Sorry if this is the wrong place to ask these questions.

Basically what I wanted was to create a set of tools that read PostGIS geometries and worked on them, all wrapped in as a Postgres extension. While that seemed straighforward enough with the PostGIS API, I'm at a loss as to how to do that with RT-Topo. I see I have to work with RTCTX, which I'm not entirely sure how to initialize, and RTT_BE_IFACE, which I'm even less certain how to set up.

Could anyone provide me with an example code that implements librttopo in a manner similar to what I intend, so I could have an idea of where to start from? I tried searching online for one, but came out empty handed.

Thanks for the attention!

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Re: [rttopo-dev] Help in using the library

a.furieri
On Mon, 30 Apr 2018 14:42:40 -0300, Roberto Ribeiro wrote:

> Hello list,
>
> I was directed here by the nice folks at the PostGIS-devel list.
> Sorry
> if this is the wrong place to ask these questions.
>
> Basically what I wanted was to create a set of tools that read
> PostGIS
> geometries and worked on them, all wrapped in as a Postgres
> extension.
> While that seemed straighforward enough with the PostGIS API, I'm at
> a
> loss as to how to do that with RT-Topo. I see I have to work with
> RTCTX, which I'm not entirely sure how to initialize, and
> RTT_BE_IFACE, which I'm even less certain how to set up.
>
> Could anyone provide me with an example code that implements
> librttopo
> in a manner similar to what I intend, so I could have an idea of
> where
> to start from? I tried searching online for one, but came out empty
> handed.
>

Hi Roberto,

the RtTopo library is mainly intended to support ISO-Topology,
although it can effectively support several advanced useful
spatial  functions not directly available when using GEOS alone
(as e.g. MakeValid, Split, Segmentize, Azimuth, 3dDistance,
3dLength and so on).

RtTopo is a derivative from PostGIS own LWGEOM, but is not
specifically intended for PostgreSQL/PostGIS, and attempts as
far as possible to support a "backend agnostic" approach.
so it necessarily requires something like "an abstract interface"
(RTCTX and RTT_BE_IFACE) intended to translate generic abstract
methods into C and SQL commands specifically intended for the
DBMS that is your current target.

AFAIK there is just one Spatial DBMS currently supporting RtTopo,
and it's SpatiaLite.
You can learn more about how-to handle RTCXT and RTT_BE_IFACE by
reading these two source files:

[1]
https://www.gaia-gis.it/fossil/libspatialite/artifact/48a145c3a56cef9c
[2]
https://www.gaia-gis.it/fossil/libspatialite/artifact/071154ce5c1aa112

but more in general, all the sources you'll find into the "topology"
directory contain many useful code examples.

bye Sandro


p.s. if you are just interested into "create a set of tools that read
PostGIS geometries and worked on them, all wrapped in as a Postgres
extension" and are not specifically interested into Topology, or
into advanced Spatial SQL Functions, or into supporting multiple
backends (MySQL, SQLite and alike) I strongly doubt that RtTopo
could be the tool you are looking for.
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