Hi Jody,
Thanks for your response.
I agree about the head hurting! Mine does already after only just
brushing the surface!
Unfortunately the exact same problem exists with WKT. In order to make
a valid WKT string for NZTM I would have to make a special case to put
the y axis first and the x axis second. Otherwise it is just exactly
the same as constructing geometries directly.
Now that I have done some more investigation trying out WKT as you
suggested, I am pretty certain this can be considered a bug in
ReferencedEnvelope; consider:
//NZMG is an x/y CRS
CoordinateReferenceSystem nzmg = CRS.decode("EPSG:27200");
//NZTM is a y/x CRS
CoordinateReferenceSystem nztm = CRS.decode("EPSG:2193");
Envelope env = new Envelope(2345678, 2345680, 6543210, 6543212);
ReferencedEnvelope refenv = ReferencedEnvelope.create(env, nzmg);
System.out.println("NZMG Envelope: " + refenv);
System.out.println("getMinimum(0): " + refenv.getMinimum(0));
System.out.println("getMinX(): " + refenv.getMinX());
refenv = refenv.transform(nztm, false);
System.out.println("NZTM Envelope: " + refenv);
System.out.println("getMinimum(0): " + refenv.getMinimum(0));
System.out.println("getMinX(): " + refenv.getMinX());
which outputs
NZMG Envelope: ReferencedEnvelope[2345678.0 : 2345680.0, 6543210.0 :
6543212.0]
getMinimum(0): 2345678.0
getMinX(): 2345678.0
NZTM Envelope: ReferencedEnvelope[5980771.101482246 : 5980773.102397159,
1435407.1134907207 : 1435409.1144056704]
getMinimum(0): 5980771.101482246
getMinX(): 5980771.101482246
which is all correct, EXCEPT the last line. The minimum X is NOT the
minimum of axis zero, and as ReferencedEnvelope is aware of the CRS and
in all other cases the CRS is aware that it is y/x should not
ReferencedEnvelope also be aware?
Were this to be fixed, might I suggest that then adding setMinX (etc)
methods to ReferencedEnvelope which were likewise CRS aware would be a
small step and (conveniently) would also resolve my original situation!
Thoughts? Thanks!
Iain
On 10/12/2016 11:25 a.m., Jody Garnett wrote:
Wow that NZTM situation is a mess; getting the wrong definition into
the EPSG database takes some skill.
Can you construct the WKT representation of what you need (to match
your data as provided) and then use GeoTools to reproject to your
final answer? I have found that making special cases based on axis
order makes my head hurt, and if I set up my definitions correct
GeoTools can construct the required transform ...
--
Jody Garnett
On 6 December 2016 at 17:44, Iain Matcham <[email protected]
<mailto:[email protected]>> wrote:
Hi all,
I have an application where I want a user to be able to enter a set of
bounds and a CRS and then the code will reproject their input into a
default CRS for further processing. A fairly simple operation:
public ReferencedEnvelope getEnvelope(
double minEast, double maxEast,
double minNorth, double maxNorth,
CoordinateReferenceSystem crs) throws TransformException,
FactoryException {
Envelope envelope = new Envelope(minEast, maxEast, minNorth,
maxNorth);
ReferencedEnvelope refEnv =
ReferencedEnvelope.create(envelope, crs);
return refEnv.transform(DEFAULT_CRS, true);
}
Except for NZTM. Thanks to LINZ, NZTM is has an axis order y/x. The
above code falls over.
Following this (admittedly quite old) thread:
http://osgeo-org.1560.x6.nabble.com/Need-help-reprojecting-ReferencedEnvelope-td5069254.html
<http://osgeo-org.1560.x6.nabble.com/Need-help-reprojecting-ReferencedEnvelope-td5069254.html>
to the suggested resolution seems to be to "Make a special case for
NZTM". Extending this to "make a special case for any y/x CRS"
means my
code now looks like:
public ReferencedEnvelope getEnvelope(
double minEast, double maxEast,
double minNorth, double maxNorth,
CoordinateReferenceSystem crs) throws TransformException,
FactoryException {
AxisDirection axisDir =
crs.getCoordinateSystem().getAxis(0).getDirection();
Envelope envelope = axisDir == AxisDirection.NORTH ?
new Envelope(minNorth, maxNorth, minEast, maxEast) :
new Envelope(minEast, maxEast, minNorth, maxNorth);
ReferencedEnvelope refEnv =
ReferencedEnvelope.create(envelope, crs);
return refEnv.transform(DEFAULT_CRS, true);
}
which seems like a lot of faff for what should be an easy operation.
But we haven't even started yet because I am pretty sure this code is
incomplete. I _think_ the real question is not are we x/y or y/x
it is
are we right handed (x/y) or left handed (y/x). So my code above
would
actually have to handle not just NORTH/EAST (right) and EAST/NORTH
(left) but also NORTH/WEST (right) or NORTHEAST/SOUTHEAST (left)
etc etc
and so on through all the permutations of AxisDirection.
So ... the only sensible resolution I can see without writing an
entire
novel of if/elses for all the possible pairs of AxisDirections is
to use
forceXY, but referring back to the discussion mentioned above, Ben
strongly discourages this.
Does anyone have any suggestions how this can be handled in a generic
non-complex way without forcing x/y axis ordering? Hopefully
someone can
help.
If not can I suggest a method
ReferencedEnvelope.create(Envelope env, CoordinateReferenceSystem crs,
boolean envelopeIsGeometric)
which (if arg2 is true) treats the envelope as x/y and does any
necessary axis conversion internally so that this piece of code can be
written once and doesn't need to be written by anyone and everyone who
might need NZTM in their app?
Would anyone else find this useful?
Thanks
Iain
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