Index: trunk/psphot/doc/2Dmodels.txt
===================================================================
--- trunk/psphot/doc/2Dmodels.txt	(revision 14727)
+++ trunk/psphot/doc/2Dmodels.txt	(revision 14728)
@@ -13,2 +13,17 @@
 job representing the variations.
 
+My new concept for modeling 2D variations in some parameter is to
+define a low-resolution 2D image to represent the variation.  The
+advantage is that the image may be define with whatever resolution may
+be sampled by the input data, and the functional form need not be
+constrained by the polynomial basis function.  
+
+** is this a poor substitute for using a chebychev polynomial as a
+   better basis function?
+
+psphot parameters which vary by position:
+
+pmPSF.params 
+pmPSF.ApTrend
+pmPSF.FluxScale (flux given normalization of 1.0)
+