RE: [Numpy-discussion] interpolating arrays (?)

[Nadav H. <na...@vi...>]

The nd_image module in numarray has a spline intrpolation function=20
(spline_filter1d). I've tried it, and it is OK.

  Nadav.

-----Original Message-----
From:	Ray Schumacher [mailto:ra...@bl...]
Sent:	Tue 23-Mar-04 03:11
To:	num...@li...
Cc:=09
Subject:	[Numpy-discussion] interpolating arrays (?)
Howdy,

I'd like to resize an array (1-dimensional) a of length n into an array =
of=20
n+x, and interpolate the values as necessary.
x might be+/-200, len(a) is usually ~500

I tried it in pure Python but it's not quite right yet. (rubberBand, =
below)
Someone out there must have done this... and linear interpolation for=20
values is probably sufficient (instead of bi-cubic or some such)

Cheers,
Ray




=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
         startSlice =3D 10000
         endOfSlice =3D=20
10000+int(round(self.samplesPerRotation))    =
#self.samplesPerRotation=3D661
         ## self.dataArray is about len=3D200,000 of Int

         for delta in range(-2,3):
             ## interpolate the different slices to the original length
	  ##  0 should return the same array, this is a test
             newArray =3D self.rubberBand(
                                 =
self.dataArray[startSlice:endOfSlice+delta],
                                 round(self.samplesPerRotation))
             print len(self.dataArray[startSlice:endOfSlice+delta]),=20
len(newArray),
             ## show the result
             print delta, =
Numeric.sum(self.dataArray[startSlice:endOfSlice]=20
- newArray)

     def rubberBand(self, data, desiredLength):
         """ alias/interpolate the data so that it is adjusted to the=20
desired array length"""
         currentLength =3D float(len(data))

         ## positive if the new array is to be longer
         difference =3D desiredLength - currentLength
         #print  difference, desiredLength, currentLength

         ## set up the desired length array
         newData =3D Numeric.zeros(desiredLength, Numeric.Float)

         ## accounts for binary rounding errors
         smallNum =3D 2**-14

         for index in range(desiredLength):
             ## find the ratio of the current index to the desired =
length
             ratio =3D index / float(desiredLength)

             ## find the same (float) position in the old data
             currIndex =3D int(ratio * currentLength)
             ## find the decimal part
             decimalPart =3D (ratio * currentLength) - currIndex
             print index, currIndex, decimalPart,
             if(decimalPart>smallNum):
                 ## interpolate
                 newData[index] =3D ((1 - decimalPart) * data[currIndex] =
+=20
decimalPart * data[currIndex+1])
                 print data[currIndex], data[currIndex+1], =
newData[index]
             else:
                 newData[index] =3D data[currIndex]
                 print 'else',data[currIndex], newData[index]

         return newData



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