| Griddata and Contour questions [message #54829] |
Wed, 11 July 2007 08:09 |
julia.kamenetzky
Messages: 1
Registered: July 2007
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Junior Member |
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I'm somewhat new to IDL, and attempting to create contour plots of
sets of astronomical data. We'd like to interpolate data points based
on the known Gaussian beam size. It seems to me like the only routine
in IDL to accomplish this would be the Kriging method of GRIDDATA
using Gaussian covariance? I have a few questions about this...
1) In what units are parameters such as d and R (as specified in the
help section on the variogram)? I am assuming that they are in units
of spacing between adjacent grid points (ie, the distance from one to
the next is equal to one), but please let me know if this is
incorrect.
2) When I use this method, I receive an array that contains values way
outside the range of the data. (My data is from about 20 to 200, and
the returned array has values from about negative to positive
12,000!) I cannot get correct results, even with changing around my
range value in the variogram, dimensions, or if I triangulate the data
before.
Some examples of ones I've tried:
KRIGGRID2=GRIDDATA(158_ASCII.L,158_ASCII.B,158_ASCII.INTENSI TY, /
KRIGING, DIMENSION=[500,386], VARIOGRAM=[3,24,0,1])
KRIGGRID=GRIDDATA(158_ASCII.L,ASCII.B,158_ASCII.INTENSITY, /KRIGING,
TRIANGLES=TR, ANISOTROPY=[1,1], DIMENSION=[500,386],
VARIOGRAM=[3,24,0,1], SEARCH_ELLIPSE=20)
Any idea what I'm doing wrong, and why I'm getting values that are
clearly not interpolations of the defined points? I am able to grid
using other methods and get reasonable contours with this data, but I
cannot seem to get this method to work.
3) Once I have this data gridded, how can I then display it on the
original coordinate axes, rather than axes that are just numbered by
indices of the gridded array?
It would be preferable to do this all using the iContour gridding
wizard (as you can tell, I have little IDL command line experience),
but as of yet I am not sure that any of the options in the wizard will
interpolate the right way. If there is a suitable option, or one that
is "close enough", I'd love to hear about it!
Thank you for your time.
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