On Mon, Apr 12, 2010 at 12:04 PM, David MacMahon
> Sounds (and looks!) interesting, Hez!
> Is this global transform applied before, after, or instead of the "pltr"
> type transformations?
> It looks like the global transform function has the same signature as the
> "pltr" transform functions so that the predefined pltr1, pltr2, etc.
> functions can be used as global transformation functions. Do you envision
> this global transform capability supplanting the individual pltr parameter
> in the functions that currently support it?
I'm glad others think that this is an interesting addition. I certainly agree!
The global transform is applied after the "pltr"-type transforms,
While the signatures are the same, I'm not sure that pltr[0-2] could
be used with plstransform in a simple manner. The intent of the
function is closer to that of the mapform parameter in plmap and
plmeridians where the transform is from unprojected world coordinates
-> projected world coordinates. If I recall correctly, the pltr*
functions transform data-grid coordinates ((0, 0) to (nx -1, ny - 1))
to world coordinates so they may not work with plstransform exactly as
they are, at least not in all cases. They do, however, still play an
Which leads to your question on supplanting per-function pltr
parameters. I think these parameters could be replaced, but I see
some value to keeping them around, at least for some PLplot functions.
For plmap and plmeridians, the mapform function parameter could be
completely replaced by plstransform as the mapform function performs a
(longitude, latitude) -> plplot world coordinate transformation. The
replacement is not as simple for plshades, plcont, plimagefr and
similar functions. In some cases, you may still want to map the data
grid values to specific coordinates and then project those coordinates
in a particular way. A meteorological example might be mapping
satellite-based precipitation observations to (longitude, latitude)
with a pltr function and then transforming (longitude, latitude) to a
particular map projection. These projections could be combined in to
one step, but splitting them up allows for a slightly more modular
design. Replace (longitude, latitude) with (RA, Dec), "precipitation"
with "M51" and "map" with "sky" for a contrived astronomical example