Hello Jan
I'm glad to hear from you :) (I was actually hoping for your reply).
Jan Jezek a écrit :
> Good news :-) I know that Krovak is little bit bizzare.
> I don't know about other projections, but in Krovak X_Scale = -1 has same
> meaning as changing the AXIS parameter from EAST to WEST in GeoTools. The
> issue is that AFAIK ESRI is ignoring the AXIS parameter (correct me if I'm
> wrong). From perspective of Krovak the X/Y-scale and XY_Plane_Rotation
> parameters are applied after whole projection.
In the Krovak projection the rotation seems to be applied after the whole
projection. But because Krovak has a false easting and false northing of zero,
the result are actually identical no matter if we apply the rotation before or
after the (easting,northing) translation. So unfortunatly Krovak is not giving
me any hints on this question.
Looking at the ObliqueMercator projection, I see that the "rectified_grid_angle"
parameter (OGC name) is called "XY_Plane_Rotation" by ESRI. I assume that ESRI
considers this parameter as the same than the one in the Krovak projection. In
the Oblique Mercator case, the rotation is clearly applied before the (easting,
northing) translation. It also make sense if we want "easting" to really means
"translation toward East" and likewise for "northing".
Because of the above, I'm tempted to assume for now that the rotation is applied
before the (easting, northing) translation. It make no difference for Krovak. If
someone with better ESRI knowledge than me correct me, I would be glad to fix
the code.
I have not checked how ESRI handles the "Transverse Mercator (South Orientated)"
case, but I would not be surprised if ESRI does exactly the same than Krovak. So
the question about whatever or not we should allow those parameters for all
projections still open... It would take me about 10 minutes to enable it for
all; I'm just not sure if it is the right thing to do.
> What I'm just not sure is how to handle the case if referencing package will
> pickup the correct axis direction parameters (e.g. Southing westing that are
> ignored by ESRI) and then it applies the ESRI parameters (X_scale... ) - then
> same wkt might be interpreted in different way by, both products - but I
> don't know if this can be solved in clean way.
In GeoTools, the projection parameters are always relative to (EAST,NORTH)
orientation. So if the projection contains PARAMETER["X_Scale", -1], etc.
elements, the axis are reversed. And if the projection contains AXIS["y", SOUTH]
elements, the axis are reversed again bringing us back to the original
(EAST,NORTH) orientation. This is probably not what ESRI intented. However maybe
we can consider that such WKT do not happen in practice? (I just hope so).
Given that if ESRI just ignore the AXIS elements, then it would be wrong for any
legal WKT having (WEST,SOUTH) orientation without the ESRI-specific extra
parameters (in which case GeoTools already produces different result than ESRI),
then maybe it is okay to consider that we would get different result in any case
where the AXIS["x", WEST], etc. element are present, no matter if
PARAMETER["X_Scale", -1]... are present or not?
Martin
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