After some experimenting it seems as if it is not possible to use the "a == a" trick to detect NaN. So I found no other way than to use a < 3.0e+36 in a NaNtoInvalid macro. -Inf will not be caught and if there already are invalid positions in the field unexpected things are probably going to happen. Interestingly enough it seems as if the constant oin the expression above needs to be a float and can not be a double.
The macro is available as a net at http://www.pdc.kth.se/%7esmeds/DX/NaNtoInvalid.net /Nils
