Hi Jody,
Thanks for getting in touch. My reply in line also:
On 26/04/13 18:34, Jody Klymak wrote:
Not clear how a direction is given as a lon lat. Do you mean you have
a set of vectors, each defined as lon/lat pairs?
My usage is to examine boundary conditions for a spectral wave model.
Thus, I have data points at locations given in**geographic coordinates
with bearings to describe the wave directions.
It depends on what you want - if you want the arrow to point where the
wind would go after X minutes, then you want the "distortion". If you
want the viewer to be able to pick off the geographic heading by eye,
then simply convert your lon lat pairs to heading/length pairs and
plot them in the axis frame. See
http://matplotlib.org/basemap/users/mapcoords.html for how to convert
from basemap to the underlying axis frame.
To clarify, the wave model I am using demands wave directions in the
projection of the grid which is being used, and I am trying to figure
out if I need to change the inputs to the wave model, using basemap as
an indicator, potentially a pre-processor.
In fact, I'm having a bit of a intellectual crisis trying to understand
what an instantaneous wave direction is and whether such a thing should
be effected by the projection it is in!
In an ideal world your projection would not be over such a large area
that any of this matters - if your vector is off by 1 degree, who will
be able to tell in a plot?
In the plots and also in the model, I think it will make very little
difference to the outputs. However, I am very interested in
quantification of uncertainty and therefore I want to demonstrate that
it could (should the directions need adjustment) make a difference to
the results, particularly if you were a bit slack with your choice of
grid projection.
Thanks again for your help and I'm sorry if this is a little "off
topic", but I know basemap users are a smart bunch to consult with. :)
All the best,
Mat
--
Dr. Mathew Topper
Institute for Energy Systems
School of Engineering
The University of Edinburgh
Faraday Building
The King's Buildings
Edinburgh EH9 3JL
Tel: +44 (0)131 650 5570
School fax: +44 (0)131 650 6554
mathew.top...@ed.ac.uk <mailto:mathew.top...@ed.ac.uk>
http://www.see.ed.ac.uk <http://www.see.ed.ac.uk/>
The University of Edinburgh is a charitable body, registered in
Scotland, with registration number SC005336.
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