| Re: matching 2 grids [message #47969 is a reply to message #47855] |
Thu, 09 March 2006 12:54   |
Mark Hadfield
Messages: 783
Registered: May 1995
|
Senior Member |
|
|
David Fanning wrote:
> I don't think this is the right approach, but I don't
> have the time to look into it at the moment. Mark is
> probably scratching his ass and getting his coffee together
> right now. He'll be with you shortly. :-)
Ta da!
Thanks for working out that MGH_MOTLEY is a script, David. To use the
Motley library you *must* add its directory to your path and you *must*
run "@MGH_MOTLEY" first.
It's MGH_EXAMPLE_LOCATE. It has 1D and 2D examples, selected by a
positional parameter called "option".
The term "index space" is one I made up (or plagiarised). Think of a 1-D
IDL array with n elements. The elements are indexed 0 to n-1. Now give
this array some values, monotonically increasing or decreasing (usually
the former) so that we can interpret the array as a 1-D grid in space.
We have a value that represents a position somewhere in the range
covered by this grid and we want to know where it is relative to the
grid. Let the grid array be x and the position we're trying to locate be
x. Let's say we find an index i such that x[i] <= xp <= x[i+1]. In fact,
let's go further and say that xp is exactly half-way between x[i] and
x[i+1]. Then I would say that xp is at position i+0.5 in the index space
of grid x.
For a 2D curvilinear grid (defined by a pair of 2D arrays) the index
space is 2D. The concept is very similar but it's a bit harder to explain.
One of the reasons "index space" is a handy concept is that it is used
by IDL's INTERPOLATE function.
To give an example of the above in terms of Motley functions:
IDL> x = mgh_range(100, 200, STRIDE=20)
IDL> print, x
100 120 140 160 180 200
IDL> xp = 133.
IDL> print, mgh_locate(x, XOUT=xp)
1.65000
--
Mark Hadfield "Kei puwaha te tai nei, Hoea tahi tatou"
m.hadfield@niwa.co.nz
National Institute for Water and Atmospheric Research (NIWA)
|
|
|
|
comp.lang.idl-pvwave archive
Members
Search
Help
Login
Home
