Colour Polar Plot

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Thu, 11/14/2013 - 02:02 am

Hi there,

I have a quick question regarding how to make a colour contour plot. I have spectral data in a table where the spectra taken are in columns, and each column is a spectrum taken at a particular angle. Ideally, I would like to make a colourmap where the spectral intensity is plotted as a colour, frequency is the radial axis and each spectrum is shown at the angle it was taken.

Any ideas would be very much appreciated!

K.
There is no direct way that I am aware of, but you could fake it. The idea is to set up a fine-grained 2D wave (i.e., an image) and calculate the intensity of this map from your data using polar coordinates. The far ends can be made invisible by using NaNs. You would need some interpolation function to do this (e.g., 'interp2D'), and then loop through your destination wave to pick values from the source (your data) while converting x + y into r + angle.

Also see this discussion for adding some labels by gluing a polar plot onto of the image: http://www.igorexchange.com/node/2606

November 14, 2013 at 02:57 am - Permalink

Thanks for the reply! In fact, I think that the data is already in the correct format for a polar plot, as the radial data is in the columns, and each column represents an angle, that's why I thought it should be relatively simple to make the plot. I also checked the idea of overlaying a polar axis onto an image, but this does not really correspond to the image we have... I thought one could "feed" the polar plot a spectrum wave and a corresponding angle, and then make the plot. If this does not work, the only real option seems to be some kind of coordinate transformation of the image, which is what I thought PolarPlot would do.

Nonetheless, thanks for the input!

November 14, 2013 at 06:30 am - Permalink

That's unfortunately not possible with the polar plot package. Actually, the polar plot in Igor produces a fake coordinate transformation of your data (points) and is not really showing a polar representation (try, for example, to get a plot to show data as bars). So for images you have to do the transformation yourself as it is not implemented (yet?). It is good that your data is already in a 'correct' format (in a x-y-kind of way), so that the coordinate transformation should be straight forward. If you don't mind posting (or sending) some representative data, I (or somebody else from the forum) could try to write a simple function for that.

November 14, 2013 at 05:58 pm - Permalink