Re: [idvusers] Vector drawing problems

Hi Reinoud-

makeVector makes grid relative vectors and you are looking for true north vectors. Change your formula to be:

makeTrueVector( newName(a/a, "u") , newName(a/a, "v") )

and you should get the vectors pointing to 45N no matter what the projection.

Don Murray

Reinoud Bokhorst wrote:
I have a problem drawing vector fields when using my own formula and custom lat/lon projections in IDV 2.7u2. It seems that the eastward component is scaled incorrectly in my own projection, i.e. the eastward component is scaled down such that my vectors always either point north- or southward.

To isolate the problem I defined a formula to make vectors with equal size u and v components (1,1):

makeVector( newName(a/a, "u") , newName(a/a, "v") )

I plotted this using 3 lat/lon projections (see attached image, zoomed in on Gulf of Aden):
- predefined 'world'
- predefined 'africa'
- custom, my own region defined using projection manager

In all 3 cases the vectors point in a different direction (they tend to rotate to the North). Only in the 'world' projection, the vectors seem correct. What's wrong?

(I have posted this question in another thread some weeks ago but haven't received an answer, apologize if I am being too impatient).


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Don Murray                               UCAR Unidata Program
dmurray@xxxxxxxxxxxxxxxx                        P.O. Box 3000
(303) 497-8628                              Boulder, CO 80307