Griddata

Greetings all,

In using the function griddata in mlab.py, I think I have found a bug. The following line in mlab.py errors for me.
I supply it an xi and yi that have shape (N,1). I have surface data, but I only care about the variation in one direction. In mlab, when it gets to this line (2956 in svn revision 7040):

          if min(xo[1:]-xo[0:-1]) < 0 or min(yo[1:]-yo[0:-1]) < 0:
              raise ValueError, 'output grid defined by xi,yi must be monotone increasing'

the result is an error. That is, I get the following:

          ValueError: min() arg is an empty sequence

A couple of things. First, if I make my variation in x to be 2 points (x = 0 for the case I'm interested in--so I just have both values of x be zero), I do not get this error and I believe the result works. So, it seems that there should be some handling of the case that there are only 1 point in either x or y direction.

Second, is it better to use the builtin python function min, or should numpy.min be used instead?

Cheers,

Josh Lawrence
Ph.D. Student
Clemson University

Josh Lawrence wrote:

Greetings all,

In using the function griddata in mlab.py, I think I have found a bug. The following line in mlab.py errors for me.
I supply it an xi and yi that have shape (N,1). I have surface data, but I only care about the variation in one direction. In mlab, when it gets to this line (2956 in svn revision 7040):

          if min(xo[1:]-xo[0:-1]) < 0 or min(yo[1:]-yo[0:-1]) < 0:
              raise ValueError, 'output grid defined by xi,yi must be monotone increasing'

the result is an error. That is, I get the following:

          ValueError: min() arg is an empty sequence

A couple of things. First, if I make my variation in x to be 2 points (x = 0 for the case I'm interested in--so I just have both values of x be zero), I do not get this error and I believe the result works. So, it seems that there should be some handling of the case that there are only 1 point in either x or y direction.

Second, is it better to use the builtin python function min, or should numpy.min be used instead?

Cheers,

Josh Lawrence
Ph.D. Student
Clemson University

Josh: griddata currently only works for 2-D output grids. It may be possible to modify it to work with 1-D data, but that was not the original intent of the function.

-Jeff

···

--
Jeffrey S. Whitaker Phone : (303)497-6313
Meteorologist FAX : (303)497-6449
NOAA/OAR/PSD R/PSD1 Email : Jeffrey.S.Whitaker@...259...
325 Broadway Office : Skaggs Research Cntr 1D-113
Boulder, CO, USA 80303-3328 Web : http://tinyurl.com/5telg

Jeff,

Thanks for the speedy reply. Should a warning be raised then that my data (though in 2D form) is not 2D and therefore is invalid input?

Cheers,

Josh Lawrence
Ph.D. Student
Clemson University

···

On Apr 16, 2009, at 2:53 PM, Jeff Whitaker wrote:

Josh Lawrence wrote:

Greetings all,

In using the function griddata in mlab.py, I think I have found a bug. The following line in mlab.py errors for me.
I supply it an xi and yi that have shape (N,1). I have surface data, but I only care about the variation in one direction. In mlab, when it gets to this line (2956 in svn revision 7040):

         if min(xo[1:]-xo[0:-1]) < 0 or min(yo[1:]-yo[0:-1]) < 0:
             raise ValueError, 'output grid defined by xi,yi must be monotone increasing'

the result is an error. That is, I get the following:

         ValueError: min() arg is an empty sequence

A couple of things. First, if I make my variation in x to be 2 points (x = 0 for the case I'm interested in--so I just have both values of x be zero), I do not get this error and I believe the result works. So, it seems that there should be some handling of the case that there are only 1 point in either x or y direction.

Second, is it better to use the builtin python function min, or should numpy.min be used instead?

Cheers,

Josh Lawrence
Ph.D. Student
Clemson University

Josh: griddata currently only works for 2-D output grids. It may be possible to modify it to work with 1-D data, but that was not the original intent of the function.

-Jeff

--
Jeffrey S. Whitaker Phone : (303)497-6313
Meteorologist FAX : (303)497-6449
NOAA/OAR/PSD R/PSD1 Email : Jeffrey.S.Whitaker@...259...
325 Broadway Office : Skaggs Research Cntr 1D-113
Boulder, CO, USA 80303-3328 Web : http://tinyurl.com/5telg

I ve a problem with the use of griddata.
I have a grid of x,y with value z. the grid have 4500 points
I would like to have a rigular grid of 1500 points.
I try the function zi = griddata(x,y,z,xi,yi)
but I have an error "too many indices". I don't understant why!!!
x,y,z,xi and yi are numpy array with 1 column.
Sorry for my bad english!!

Thanks

Josh Lawrence-2 wrote:

···

Greetings all,

In using the function griddata in mlab.py, I think I have found a bug.
The following line in mlab.py errors for me.
I supply it an xi and yi that have shape (N,1). I have surface data,
but I only care about the variation in one direction. In mlab, when it
gets to this line (2956 in svn revision 7040):

          if min(xo[1:]-xo[0:-1]) < 0 or min(yo[1:]-yo[0:-1]) < 0:
              raise ValueError, 'output grid defined by xi,yi must be
monotone increasing'

the result is an error. That is, I get the following:

          ValueError: min() arg is an empty sequence

A couple of things. First, if I make my variation in x to be 2 points
(x = 0 for the case I'm interested in--so I just have both values of x
be zero), I do not get this error and I believe the result works. So,
it seems that there should be some handling of the case that there are
only 1 point in either x or y direction.

Second, is it better to use the builtin python function min, or should
numpy.min be used instead?

Cheers,

Josh Lawrence
Ph.D. Student
Clemson University

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