From: Paul Wellner Bou <paul@pu...>  20080314 10:01:35

Hello, Thank you for your answer. > Since your pattern of points is confined to a circular area (and rather > complete within that area), my suggestion is to try using polar coordinates > throughout. Now example 21 obviously uses rectangular coordinates for > plgriddata, but I presume plgriddata should work just as it is for any > twodimensional coordinate system. Yes, this should work. I will have a look. Not sure if there is the time to implement this. Perhaps it is easier to calculate the rays which intersect with the eye glass in exactly the points of a rectangular grid. > Furthermore, example 16's last page (see > http://plplot.sourceforge.net/examplesdata/demo16/x16.05.png) shows > plshades can be used with any twodimensional coordinate system. Ok, this looks good. This example shows me that it is possible to draw a graph of a circle without filling the whole rectangle. >> Is there a way to use the DTLI algorithm to get a kind of data like in >> http://m21s26.vlinux.de/math/gsg.png? > > I think yes. Once you get plgriddata and plshades working for polar > coordinates it should be a simple matter to use plbox to make a rectangular > box around the circular area created by plshades. You can arrange the plbox > call so the tick marks on the box are for rectangular coordinates > corresponding to the polar coordinates used for plshades. Puh... I don't understand this at this moment. I'll have to dive into it. Converting it to polar coordinates, ok. This should be no problem. Then I would get (I hope so...) a regular grid in polar coordinates. But if I convert it back it may not be regular, in xy, right? Hm, not sure how to implement this, but it should be possible in any way. Thank you and regards Paul. 