On Mar 18, 4:56 pm, millward.geo...@gmail.com wrote:
> Hi there,
>
> I am trying to use particle_trace to create streamlines from a vector
> field - but I'm having quite alot of trouble
> understanding the documentation.
>
> I have a velocity field which is a longitude,latitude array of
> Southward and Eastward velocities.
> My arrays are 20 longitudes by 91 latitudes. So my 2 arrays are:
>
> V_south(20,91) and V_east(20,91)
>
> I now want to feed these into Particle_trace.
>
> The syntax for Particle_trace requires a single array (which they call
> Data) of
> size Data[2,dx,dy]
>
> I'm assuming that dx and dy are the indexes for longitude and latitude
> and the first dimension (2)
> is for the 2 components of the field, so:
>
> data(0,lon,lat) = V_east(lon,lat)
> data(1,lon,lat) = 0.0 - V_south(lon,lat)
>
> Nowhere in the documentation does it define the directions - is dx
> Eastwards - is dy Northwards? Very confusing !!
>
> And the seed points - are these longitude, latitude points or
> something ? Again, no real explanation in the documentation.
>
> ....or have I got it completely wrong ?
>
> Any help with this very much appreciated
>
> Cheers,
>
> George.
Here's an example of using PARTICLE_TRACE:
; defines u, v, x, and y
restore, filepath('globalwinds.dat', subdir=['examples','data'])
data = fltarr(2, 128, 64)
data[0, *, *] = u
data[1, *, *] = v
; define starting points
seeds = [[32, 32], [64, 32], [96, 32]]
particle_trace, data, seeds, verts, conn, max_iterations=30
; plot the underlying vector field
velovect, u, v, x, y
; overplot the streamlines
i = 0
sz = size(verts, /structure)
while (i lt sz.dimensions[1]) do begin
nverts = conn[i]
plots, x[verts[0, conn[i+1:i+nverts]]], y[verts[1, conn[i+1:i
+nverts]]], $
color='0000FF'x, thick=2, linestyle=2
i += nverts + 1
endwhile
Mike
--
www.michaelgalloy.com
Tech-X Corporation
Software Developer II
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