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Re: Direction of Wind Vectors: A bug? [message #90343 is a reply to message #90287]

Mon, 23 February 2015 07:28

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

David Fanning writes:

> Someone was harassing my retirement reveries this morning by claiming
> that cgDrawVectors was drawing vectors incorrectly, in the wrong
> directions. He cited as evidence the output of the lovely NASA program,
> PartVelVec.

Having decided Wayne was doing the right thing, and still a bit
dissatisfied with how my cgDrawVectors algorithm was working, I spent
the weekend (the reason I retired!) completely gutting and rebuilding
cgDrawVectors. It now takes into account the scale of the plot in the X
and Y directions. What took me a while to work out is that the scale of
the plot on a map projection should always be 180x360, no matter what
portion of the map you are showing in the plot.

Making these changes, I can duplicate the PartVelVec results on every
test I've made, including tests with map projections using Map_Set and
the Map_Proj_Init methods (as implemented in cgMap_Set and cgMap). I've
tried various map projections, and all seems to be working correctly,
although additional testing on ALL map projections is probably
warranted.

While I was tearing things up, I decided to fix the code in cgArrow
(which was drawing the vectors) to make it more flexible and faster by
moving the code closer to the machine. You can now pass a vector of
colors to cgArrow, as well as a vector of arrows to draw, and you should
see significant speed-up of its vector drawing capability. Both programs
should be downloaded, as cgDrawVectors depends on cgArrow.

You can find the two new programs here:

http://www.idlcoyote.com/programs/cgarrow.pro
http://www.idlcoyote.com/programs/cgdrawvectors.pro

Cheers,

David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
Sepore ma de ni thue. ("Perhaps thou speakest truth.")

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[Message index]

		Direction of Wind Vectors: A bug? By: David Fanning on Wed, 18 February 2015 10:32
		Re: Direction of Wind Vectors: A bug? By: wlandsman on Wed, 18 February 2015 11:23
		Re: Direction of Wind Vectors: A bug? By: David Fanning on Wed, 18 February 2015 11:44
		Re: Direction of Wind Vectors: A bug? By: natha on Wed, 18 February 2015 12:04
		Re: Direction of Wind Vectors: A bug? By: David Fanning on Wed, 18 February 2015 12:09
		Re: Direction of Wind Vectors: A bug? By: Paul Van Delst[1] on Wed, 18 February 2015 12:25
		Re: Direction of Wind Vectors: A bug? By: David Fanning on Wed, 18 February 2015 12:46
		Re: Direction of Wind Vectors: A bug? By: David Fanning on Wed, 18 February 2015 14:23
		Re: Direction of Wind Vectors: A bug? By: Fabzi on Wed, 18 February 2015 14:27
		Re: Direction of Wind Vectors: A bug? By: David Fanning on Wed, 18 February 2015 14:44
		Re: Direction of Wind Vectors: A bug? By: David Fanning on Mon, 23 February 2015 07:28

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