I forgot to mention that the data input is SCEC CMM4, with GPS and EDM secular station velocities included. On Fri, Mar 26, 2010 at 2:11 PM, Zhengkang Shen wrote: Dear Dave, Attached please find our data file. Interpolation is done using a weighting function based on azimuthal span and gaussian distance, and the decay distance constant is determined from a trade-off between the solution uncertainty and the weighting coefficient. Stations located in the 'shadow zone' behind the creeping section of the San Andreas are also screened out from the interpolation. The data file contains more items than you need, the ones relevant to your comparison are lat, lon, e11, e12, and e22. '1' means east and '2' means north. You can discard the rest.