Hello César
Le 19/02/2018 à 17:34, César Martínez Izquierdo a écrit :
> - After parsing an ESRI WKT, I'd like to get the equivalent EPSG
> definition. Is there a way to achieve this?
>
Yes. A first thing to do is to not use the CRS.fromWKT(String)
convenience method because that method parses standard WKT as defined by
ISO 19162 (WKT 2) or OGC 01-009 (WKT 1), while ESRI WKT 1 and GDAL
differs from those standards (note: latest ESRI products support WKT 2
in the standard way, but did not changed their WKT 1 for compatibility
reasons). We have to use WKTFormat for instructing Apache SIS to parse
non-standard WKT 1:
WKTFormat parser = new WKTFormat(null, null);
parser.setConvention(Convention.WKT1_COMMON_UNITS);
See http://sis.apache.org/apidocs/org/apache/sis/io/wkt/Convention.html
for more information. You may also consider using
Convention.WKT1_IGNORE_AXES, which I think is GDAL behaviour. Then you
can parse with parseObject(String) method.
After having a CRS, we can search for its identifier code with following
convenience method:
Integer code = IdentifiedObjects.lookupEPSG(crs);
Note that this method is likely to return null for most geographic
objects, because axis orders used by GDAL (and I think also ESRI before
their upgrade to WKT 2) differ from EPSG definitions. If you want to get
an EPSG code despite the difference in axis order, see
http://sis.apache.org/apidocs/org/apache/sis/referencing/IdentifiedObjects.html#newFinder-java.lang.String-
> I've seen that there is ESRI citations in the providers, but I don't
> know how to use them.
>
The ESRI citations are used for map projection parameters, which
sometime differs from other authorities. For example on
http://sis.apache.org/tables/CoordinateOperationMethods.html#9822 click
on "Latitude of false origin". This allows SIS to be able to parse ESRI
WKT despite differences in parameter names. But there is not ESRI
definitions of CRS in SIS yet (as far as I remember).
> I've tried the following code:
>
> (…snip…)
> crs = CRS.fromAuthority(crs, factory, null);
>
> However, the resulting CRS still looks an ESRI one.
>
Did it returns the same instance (return value == argument)?
> - There is a database of ESRI codes in the CRS library we are
> currently using in gvSIG. If we were willing to use this database with
> Apache SIS, I assume we should create a plugin which provides a new
> authority factory. Am I right Is this feasible?
>
Yes, there is already a JIRA task for that:
https://issues.apache.org/jira/browse/SIS-117
Note that when using WKTFormat, it is possible to define shortcut for
frequently used elements:
http://sis.apache.org/apidocs/org/apache/sis/io/wkt/WKTFormat.html#addFragment-java.lang.String-java.lang.String-
It does not only make the definition files smaller, but also faster to
parse and consume less memory (in above example, every time $MyEllipsoid
is used, SIS share the parsed tree - it is not just a search-and-replace
of texts).
Martin
