[gdal-dev] Achieving Better WKT -> EPSG Code Autodetection When Importing Layers to Postgis

[Andrea Aime]

Hi Even,
just a quick note about GeoTools and http://prj2epsg.org

In terms of matching via GeoTools, we have spent quite some time building
tables of aliases and
some lax equivalence rules, think DMS is same a deegree, some tolerance on
the parameter
values, and so on.

prj2epsg.org uses that (a much older version of it actually) along with
pure and simple full text search matches.

It basically extracts a set of keywords from the WKT and searches against a
similar database
built by indexing all of the EPSG database contents. This is actually what
happens when you put
in that prj file, the result you're pointing to is the 3rd match.
If you input instead something that is actually equivalent, then you'll get
a single result.

Looks like Boundless made the old code for the site publicly available on
github really recently:
https://github.com/boundlessgeo/prj2epsg
Still using a GeoTools 2.6.6, oh dear! :-)

Cheers
Andrea


On Sat, Sep 23, 2017 at 11:19 AM, Even Rouault <even.rouault at spatialys.com>
wrote:

> > I've had this issue for years, but concede I might be missing something.
> Is
>
> > there anything that can remedy this issue utilizing existing
> functionality?
>
>
>
> No need for a complicated thing like a JNI bridge, but someone has to code
> it in GDAL. All the basic functionnality is there. Just needs to be put
> together. A basic approach would be to iterate over the EPSG codes from the
> gcs.csv and pcs.csv files, use importFromEPSG() and compare the resulting
> WKT with the user WKT. Some fuzzing would be needed to be robust to slight
> naming variations, etc. This was actually an idea for a GSoc project, but
> anyone is free to pick it up and bring his/her contribution.
>
>
>
> In the .prj you pointed, prj2epsg first suggestion, EPSG:32139, is
> actually completely inappropriate given it uses meter as linear unit,
> whereas the .prj uses foot_us. EPSG:2277 looks to be the exact match. And
> another interesting thing is that the .prj has Standard_Parallel_1 =
> 30.11666666666667 and Standard_Parallel_2 = 31.88333333333333. Whereas
> EPSG:2277 has them in the reverse order. Which is equivalent
> mathematically, but a matcher should be aware of that equivalence. So not
> completely a trivial task.
>
>
>
> Even
>
>
>
> --
>
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-- 

Regards,

Andrea Aime

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