Index: trunk/psModules/src/objects/models/pmModel_GAUSS.c
===================================================================
--- trunk/psModules/src/objects/models/pmModel_GAUSS.c	(revision 9730)
+++ trunk/psModules/src/objects/models/pmModel_GAUSS.c	(revision 9770)
@@ -1,37 +1,52 @@
-#ifdef HAVE_CONFIG_H
-#include <config.h>
-#endif
-
 /******************************************************************************
-    params->data.F32[PM_PAR_SKY] = So;
-    params->data.F32[PM_PAR_I0] = Zo;
-    params->data.F32[PM_PAR_XPOS] = Xo;
-    params->data.F32[PM_PAR_YPOS] = Yo;
-    params->data.F32[PM_PAR_SXX] = sqrt(2.0) / SigmaX;
-    params->data.F32[PM_PAR_SYY] = sqrt(2.0) / SigmaY;
-    params->data.F32[PM_PAR_SXY] = Sxy;
-*****************************************************************************/
-
-psF32 pmModelFunc_GAUSS(psVector *deriv,
-                        const psVector *params,
-                        const psVector *x)
-{
-    psF32 X  = x->data.F32[0] - params->data.F32[PM_PAR_XPOS];
-    psF32 Y  = x->data.F32[1] - params->data.F32[PM_PAR_YPOS];
-    psF32 px = params->data.F32[PM_PAR_SXX]*X;
-    psF32 py = params->data.F32[PM_PAR_SYY]*Y;
-    psF32 z  = 0.5*PS_SQR(px) + 0.5*PS_SQR(py) + params->data.F32[PM_PAR_SXY]*X*Y;
+ * this file defines the PGAUSS source shape model.  Note that these model functions are loaded
+ * by pmModelGroup.c using 'include', and thus need no 'include' statements of their own.  The
+ * models use a psVector to represent the set of parameters, with the sequence used to specify
+ * the meaning of the parameter.  The meaning of the parameters may thus vary depending on the
+ * specifics of the model.  All models which are used a PSF representations share a few
+ * parameters, for which # define names are listed in pmModel.h:
+ 
+ * PM_PAR_SKY 0   - local sky : note that this is unused and may be dropped in the future
+ * PM_PAR_I0 1    - central intensity
+ * PM_PAR_XPOS 2  - X center of object
+ * PM_PAR_YPOS 3  - Y center of object
+ * PM_PAR_SXX 4   - X^2 term of elliptical contour (sqrt(2) / SigmaX)
+ * PM_PAR_SYY 5   - Y^2 term of elliptical contour (sqrt(2) / SigmaY)
+ * PM_PAR_SXY 6   - X*Y term of elliptical contour
+ *****************************************************************************/
+
+# define PM_MODEL_FUNC       pmModelFunc_GAUSS
+# define PM_MODEL_FLUX       pmModelFlux_GAUSS
+# define PM_MODEL_GUESS      pmModelGuess_GAUSS
+# define PM_MODEL_LIMITS     pmModelLimits_GAUSS
+# define PM_MODEL_RADIUS     pmModelRadius_GAUSS
+# define PM_MODEL_FROM_PSF   pmModelFromPSF_GAUSS
+# define PM_MODEL_FIT_STATUS pmModelFitStatus_GAUSS
+
+psF32 PM_MODEL_FUNC(psVector *deriv,
+                    const psVector *params,
+                    const psVector *pixcoord)
+{
+    psF32 *PAR = params->data.F32;
+
+    // XXX this is fitting sqrt(2)/sigma_x, sqrt(2)/sigma_y
+    psF32 X  = pixcoord->data.F32[0] - PAR[PM_PAR_XPOS];
+    psF32 Y  = pixcoord->data.F32[1] - PAR[PM_PAR_YPOS];
+    psF32 px = X / PAR[PM_PAR_SXX];
+    psF32 py = Y / PAR[PM_PAR_SYY];
+    psF32 z  = PS_SQR(px) + PS_SQR(py) + PAR[PM_PAR_SXY]*X*Y;
     psF32 r  = exp(-z);
-    psF32 q  = params->data.F32[PM_PAR_I0]*r;
-    psF32 f  = q + params->data.F32[PM_PAR_SKY];
+    psF32 q  = PAR[PM_PAR_I0]*r;
+    psF32 f  = q + PAR[PM_PAR_SKY];
 
     if (deriv != NULL) {
-        deriv->data.F32[PM_PAR_SKY] = +1.0;
-        deriv->data.F32[PM_PAR_I0] = +r;
-        deriv->data.F32[PM_PAR_XPOS] = q*(2*px*params->data.F32[PM_PAR_SXX] + params->data.F32[PM_PAR_SXY]*Y);
-        deriv->data.F32[PM_PAR_YPOS] = q*(2*py*params->data.F32[PM_PAR_SYY] + params->data.F32[PM_PAR_SXY]*X);
-        deriv->data.F32[PM_PAR_SXX] = -2.0*q*px*X;
-        deriv->data.F32[PM_PAR_SYY] = -2.0*q*py*Y;
-        deriv->data.F32[PM_PAR_SXY] = -q*X*Y;
+        psF32 *dPAR = deriv->data.F32;
+        dPAR[PM_PAR_SKY]  = +1.0;
+        dPAR[PM_PAR_I0]   = +r;
+        dPAR[PM_PAR_XPOS] = q*(2*px/PAR[PM_PAR_SXX] + Y*PAR[PM_PAR_SXY]);
+        dPAR[PM_PAR_YPOS] = q*(2*py/PAR[PM_PAR_SYY] + X*PAR[PM_PAR_SXY]);
+        dPAR[PM_PAR_SXX]  = +2.0*q*px*px/PAR[PM_PAR_SXX];
+        dPAR[PM_PAR_SYY]  = +2.0*q*py*py/PAR[PM_PAR_SYY];
+        dPAR[PM_PAR_SXY]  = -q*X*Y;
     }
     return(f);
@@ -39,5 +54,5 @@
 
 // define the parameter limits
-bool pmModelLimits_GAUSS (psVector **beta_lim, psVector **params_min, psVector **params_max)
+bool PM_MODEL_LIMITS (psVector **beta_lim, psVector **params_min, psVector **params_max)
 {
 
@@ -58,6 +73,6 @@
     params_min[0][0].data.F32[PM_PAR_XPOS] = -100;
     params_min[0][0].data.F32[PM_PAR_YPOS] = -100;
-    params_min[0][0].data.F32[PM_PAR_SXX] = 0.01;
-    params_min[0][0].data.F32[PM_PAR_SYY] = 0.01;
+    params_min[0][0].data.F32[PM_PAR_SXX] = 0.5;
+    params_min[0][0].data.F32[PM_PAR_SYY] = 0.5;
     params_min[0][0].data.F32[PM_PAR_SXY] = -5.0;
 
@@ -66,6 +81,6 @@
     params_max[0][0].data.F32[PM_PAR_XPOS] = 1e4;  // this should be set by image dimensions!
     params_max[0][0].data.F32[PM_PAR_YPOS] = 1e4;  // this should be set by image dimensions!
-    params_max[0][0].data.F32[PM_PAR_SXX] = 2.0;
-    params_max[0][0].data.F32[PM_PAR_SYY] = 2.0;
+    params_max[0][0].data.F32[PM_PAR_SXX] = 100.0;
+    params_max[0][0].data.F32[PM_PAR_SYY] = 100.0;
     params_max[0][0].data.F32[PM_PAR_SXY] = +5.0;
 
@@ -74,27 +89,34 @@
 
 // make an initial guess for parameters
-bool pmModelGuess_GAUSS (pmModel *model, pmSource *source)
+bool PM_MODEL_GUESS (pmModel *model, pmSource *source)
 {
 
     pmMoments *moments = source->moments;
-    psF32     *params  = model->params->data.F32;
-
-    params[PM_PAR_SKY] = moments->Sky;
-    params[PM_PAR_I0] = moments->Peak - moments->Sky;
-    params[PM_PAR_XPOS] = moments->x;
-    params[PM_PAR_YPOS] = moments->y;
-    params[PM_PAR_SXX] = (moments->Sx < (1.2 / 2.0)) ? 2.0 : (1.2 / moments->Sx);
-    params[PM_PAR_SYY] = (moments->Sy < (1.2 / 2.0)) ? 2.0 : (1.2 / moments->Sy);
-    params[PM_PAR_SXY] = 0.0;
+    psF32     *PAR  = model->params->data.F32;
+
+    PAR[PM_PAR_SKY] = moments->Sky;
+    PAR[PM_PAR_I0] = moments->Peak - moments->Sky;
+    PAR[PM_PAR_XPOS] = moments->x;
+    PAR[PM_PAR_YPOS] = moments->y;
+    PAR[PM_PAR_SXX] = PS_MAX(0.5, moments->Sx);
+    PAR[PM_PAR_SYY] = PS_MAX(0.5, moments->Sy);
+    PAR[PM_PAR_SXY] = 0.0;
     return(true);
 }
 
-psF64 pmModelFlux_GAUSS(const psVector *params)
-{
-    psF64 A1   = PS_SQR(params->data.F32[PM_PAR_SXX]);
-    psF64 A2   = PS_SQR(params->data.F32[PM_PAR_SYY]);
-    psF64 A3   = PS_SQR(params->data.F32[PM_PAR_SXY]);
-    psF64 Area = 2.0 * M_PI / sqrt(A1*A2 - A3);
+psF64 PM_MODEL_FLUX (const psVector *params)
+{
+
+    psEllipseShape shape;
+
+    psF32 *PAR = params->data.F32;
+
+    shape.sx  = PAR[PM_PAR_SXX] / sqrt(2.0);
+    shape.sy  = PAR[PM_PAR_SYY] / sqrt(2.0);
+    shape.sxy = PAR[PM_PAR_SXY] / sqrt(2.0);
+
     // Area is equivalent to 2 pi sigma^2
+    psEllipseAxes axes = psEllipseShapeToAxes (shape);
+    psF64 Area = 2.0 * M_PI * axes.major * axes.minor;
 
     psF64 Flux = params->data.F32[PM_PAR_I0] * Area;
@@ -105,6 +127,7 @@
 // return the radius which yields the requested flux
 // this function is never allowed to return <= 0
-psF64 pmModelRadius_GAUSS  (const psVector *params, psF64 flux)
-{
+psF64 PM_MODEL_RADIUS (const psVector *params, psF64 flux)
+{
+    psEllipseShape shape;
 
     if (flux <= 0)
@@ -115,11 +138,17 @@
         return (1.0);
 
-    psF64 sigma  = sqrt(2.0) * hypot (1.0 / params->data.F32[PM_PAR_SXX], 1.0 / params->data.F32[PM_PAR_SYY]);
-    psF64 radius = sigma * sqrt (2.0 * log(params->data.F32[PM_PAR_I0] / flux));
+    psF32 *PAR = params->data.F32;
+
+    shape.sx  = PAR[PM_PAR_SXX] / sqrt(2.0);
+    shape.sy  = PAR[PM_PAR_SYY] / sqrt(2.0);
+    shape.sxy = PAR[PM_PAR_SXY] / sqrt(2.0);
+
+    psEllipseAxes axes = psEllipseShapeToAxes (shape);
+    psF64 radius = axes.major * sqrt (2.0 * log(params->data.F32[PM_PAR_I0] / flux));
     return (radius);
 }
 
 // construct the PSF model from the FLT model and the psf
-bool pmModelFromPSF_GAUSS (pmModel *modelPSF, pmModel *modelFLT, pmPSF *psf)
+bool PM_MODEL_FROM_PSF (pmModel *modelPSF, pmModel *modelFLT, pmPSF *psf)
 {
 
@@ -127,19 +156,28 @@
     psF32 *in  = modelFLT->params->data.F32;
 
-    out[PM_PAR_SKY] = in[PM_PAR_SKY];
-    out[PM_PAR_I0] = in[PM_PAR_I0];
-    out[PM_PAR_XPOS] = in[PM_PAR_XPOS];
-    out[PM_PAR_YPOS] = in[PM_PAR_YPOS];
-
-    assert (PM_PAR_YPOS + 1 == 4);  // so starting at 4 is correct
-    for (int i = 4; i < 7; i++) {
-        psPolynomial2D *poly = psf->params->data[i-4];
-        out[i] = psPolynomial2DEval(poly, out[PM_PAR_XPOS], out[PM_PAR_YPOS]);
+    // we require these two parameters to exist
+    assert (psf->params_NEW->n > PM_PAR_YPOS);
+    assert (psf->params_NEW->n > PM_PAR_XPOS);
+
+    // supply the model-fitted parameters, or copy from the input
+    for (int i = 0; i < psf->params_NEW->n; i++) {
+        if (psf->params_NEW->data[i] == NULL) {
+            out[i] = in[i];
+        } else {
+            psPolynomial2D *poly = psf->params_NEW->data[i];
+            out[i] = psPolynomial2DEval(poly, in[PM_PAR_XPOS], in[PM_PAR_YPOS]);
+        }
     }
+
+    // the 2D model for SXY actually fits SXY / (SXX^-2 + SYY^-2); correct here
+    out[PM_PAR_SXY] = pmPSF_SXYtoModel (out);
+
     return(true);
 }
 
 // check the status of the fitted model
-bool pmModelFitStatus_GAUSS (pmModel *model)
+// this test is invalid if the parameters are derived
+// from the PSF model
+bool PM_MODEL_FIT_STATUS (pmModel *model)
 {
 
@@ -164,2 +202,10 @@
     return false;
 }
+
+# undef PM_MODEL_FUNC
+# undef PM_MODEL_FLUX
+# undef PM_MODEL_GUESS
+# undef PM_MODEL_LIMITS
+# undef PM_MODEL_RADIUS
+# undef PM_MODEL_FROM_PSF
+# undef PM_MODEL_FIT_STATUS
Index: trunk/psModules/src/objects/models/pmModel_PGAUSS.c
===================================================================
--- trunk/psModules/src/objects/models/pmModel_PGAUSS.c	(revision 9730)
+++ trunk/psModules/src/objects/models/pmModel_PGAUSS.c	(revision 9770)
@@ -1,46 +1,58 @@
-#ifdef HAVE_CONFIG_H
-#include <config.h>
-#endif
-
 /******************************************************************************
-    params->data.F32[0] = So;
-    params->data.F32[1] = Zo;
-    params->data.F32[2] = Xo;
-    params->data.F32[3] = Yo;
-    params->data.F32[4] = sqrt(2.0) / SigmaX;
-    params->data.F32[5] = sqrt(2.0) / SigmaY;
-    params->data.F32[6] = Sxy;
-*****************************************************************************/
-
-psF32 pmModelFunc_PGAUSS(psVector *deriv,
-                         const psVector *params,
-                         const psVector *x)
+ * this file defines the PGAUSS source shape model.  Note that these model functions are loaded
+ * by pmModelGroup.c using 'include', and thus need no 'include' statements of their own.  The
+ * models use a psVector to represent the set of parameters, with the sequence used to specify
+ * the meaning of the parameter.  The meaning of the parameters may thus vary depending on the
+ * specifics of the model.  All models which are used a PSF representations share a few
+ * parameters, for which # define names are listed in pmModel.h:
+ 
+ * PM_PAR_SKY 0   - local sky : note that this is unused and may be dropped in the future
+ * PM_PAR_I0 1    - central intensity
+ * PM_PAR_XPOS 2  - X center of object
+ * PM_PAR_YPOS 3  - Y center of object
+ * PM_PAR_SXX 4   - X^2 term of elliptical contour (sqrt(2) / SigmaX)
+ * PM_PAR_SYY 5   - Y^2 term of elliptical contour (sqrt(2) / SigmaY)
+ * PM_PAR_SXY 6   - X*Y term of elliptical contour
+ *****************************************************************************/
+
+# define PM_MODEL_FUNC       pmModelFunc_PGAUSS
+# define PM_MODEL_FLUX       pmModelFlux_PGAUSS
+# define PM_MODEL_GUESS      pmModelGuess_PGAUSS
+# define PM_MODEL_LIMITS     pmModelLimits_PGAUSS
+# define PM_MODEL_RADIUS     pmModelRadius_PGAUSS
+# define PM_MODEL_FROM_PSF   pmModelFromPSF_PGAUSS
+# define PM_MODEL_FIT_STATUS pmModelFitStatus_PGAUSS
+
+// the model is a function of the pixel coordinate (pixcoord[0,1] = x,y)
+psF32 PM_MODEL_FUNC(psVector *deriv,
+                    const psVector *params,
+                    const psVector *pixcoord)
 {
     psF32 *PAR = params->data.F32;
 
-    psF32 X  = x->data.F32[0] - PAR[2];
-    psF32 Y  = x->data.F32[1] - PAR[3];
-    psF32 px = PAR[4]*X;
-    psF32 py = PAR[5]*Y;
-    psF32 z  = 0.5*PS_SQR(px) + 0.5*PS_SQR(py) + PAR[6]*X*Y;
+    psF32 X  = pixcoord->data.F32[0] - PAR[PM_PAR_XPOS];
+    psF32 Y  = pixcoord->data.F32[1] - PAR[PM_PAR_YPOS];
+    psF32 px = X / PAR[PM_PAR_SXX];
+    psF32 py = Y / PAR[PM_PAR_SYY];
+    psF32 z  = PS_SQR(px) + PS_SQR(py) + PAR[PM_PAR_SXY]*X*Y;
     psF32 t  = 1 + z + z*z/2.0;
     psF32 r  = 1.0 / (t + z*z*z/6.0); /* exp (-Z) */
-    psF32 f  = PAR[1]*r + PAR[0];
+    psF32 f  = PAR[PM_PAR_I0]*r + PAR[PM_PAR_SKY];
 
     if (deriv != NULL) {
         psF32 *dPAR = deriv->data.F32;
-        psF32 q = PAR[1]*r*r*t;
-        dPAR[0] = +1.0;
-        dPAR[1] = +r;
-        dPAR[2] = q*(2.0*px*PAR[4] + PAR[6]*Y);
-        dPAR[3] = q*(2.0*py*PAR[5] + PAR[6]*X);
-        dPAR[4] = -2.0*q*px*X;
-        dPAR[5] = -2.0*q*py*Y;
-        dPAR[6] = -q*X*Y;
+        psF32 q = PAR[PM_PAR_I0]*r*r*t;
+        dPAR[PM_PAR_SKY] = +1.0;
+        dPAR[PM_PAR_I0] = +r;
+        dPAR[PM_PAR_XPOS] = q*(2.0*px/PAR[PM_PAR_SXX] + Y*PAR[PM_PAR_SXY]);
+        dPAR[PM_PAR_YPOS] = q*(2.0*py/PAR[PM_PAR_SYY] + X*PAR[PM_PAR_SXY]);
+        dPAR[PM_PAR_SXX] =  +2.0*q*px*px/PAR[PM_PAR_SXX];
+        dPAR[PM_PAR_SYY] =  +2.0*q*py*py/PAR[PM_PAR_SYY];
+        dPAR[PM_PAR_SXY] = -q*X*Y;
     }
     return(f);
 }
 
-bool pmModelLimits_PGAUSS (psVector **beta_lim, psVector **params_min, psVector **params_max)
+bool PM_MODEL_LIMITS (psVector **beta_lim, psVector **params_min, psVector **params_max)
 {
 
@@ -49,27 +61,27 @@
     *params_max = psVectorAlloc (7, PS_TYPE_F32);
 
-    beta_lim[0][0].data.F32[0] = 1000;
-    beta_lim[0][0].data.F32[1] = 3e6;
-    beta_lim[0][0].data.F32[2] = 5;
-    beta_lim[0][0].data.F32[3] = 5;
-    beta_lim[0][0].data.F32[4] = 0.5;
-    beta_lim[0][0].data.F32[5] = 0.5;
-    beta_lim[0][0].data.F32[6] = 0.5;
-
-    params_min[0][0].data.F32[0] = -1000;
-    params_min[0][0].data.F32[1] = 0;
-    params_min[0][0].data.F32[2] = -100;
-    params_min[0][0].data.F32[3] = -100;
-    params_min[0][0].data.F32[4] = 0.01;
-    params_min[0][0].data.F32[5] = 0.01;
-    params_min[0][0].data.F32[6] = -5.0;
-
-    params_max[0][0].data.F32[0] = 1e5;
-    params_max[0][0].data.F32[1] = 1e8;
-    params_max[0][0].data.F32[2] = 1e4;  // this should be set by image dimensions!
-    params_max[0][0].data.F32[3] = 1e4;  // this should be set by image dimensions!
-    params_max[0][0].data.F32[4] = 2.0;
-    params_max[0][0].data.F32[5] = 2.0;
-    params_max[0][0].data.F32[6] = +5.0;
+    beta_lim[0][0].data.F32[PM_PAR_SKY] = 1000;
+    beta_lim[0][0].data.F32[PM_PAR_I0] = 3e6;
+    beta_lim[0][0].data.F32[PM_PAR_XPOS] = 5;
+    beta_lim[0][0].data.F32[PM_PAR_YPOS] = 5;
+    beta_lim[0][0].data.F32[PM_PAR_SXX] = 0.5;
+    beta_lim[0][0].data.F32[PM_PAR_SYY] = 0.5;
+    beta_lim[0][0].data.F32[PM_PAR_SXY] = 0.5;
+
+    params_min[0][0].data.F32[PM_PAR_SKY] = -1000;
+    params_min[0][0].data.F32[PM_PAR_I0] = 0;
+    params_min[0][0].data.F32[PM_PAR_XPOS] = -100;
+    params_min[0][0].data.F32[PM_PAR_YPOS] = -100;
+    params_min[0][0].data.F32[PM_PAR_SXX] = 0.5;
+    params_min[0][0].data.F32[PM_PAR_SYY] = 0.5;
+    params_min[0][0].data.F32[PM_PAR_SXY] = -5.0;
+
+    params_max[0][0].data.F32[PM_PAR_SKY] = 1e5;
+    params_max[0][0].data.F32[PM_PAR_I0] = 1e8;
+    params_max[0][0].data.F32[PM_PAR_XPOS] = 1e4;  // this should be set by image dimensions!
+    params_max[0][0].data.F32[PM_PAR_YPOS] = 1e4;  // this should be set by image dimensions!
+    params_max[0][0].data.F32[PM_PAR_SXX] = 100.0;
+    params_max[0][0].data.F32[PM_PAR_SYY] = 100.0;
+    params_max[0][0].data.F32[PM_PAR_SXY] = +5.0;
 
     return (TRUE);
@@ -77,32 +89,35 @@
 
 // make an initial guess for parameters
-bool pmModelGuess_PGAUSS (pmModel *model, pmSource *source)
+bool PM_MODEL_GUESS (pmModel *model, pmSource *source)
 {
 
     pmMoments *moments = source->moments;
-    psF32     *params  = model->params->data.F32;
-
-    params[0] = moments->Sky;
-    params[1] = moments->Peak - moments->Sky;
-    params[2] = moments->x;
-    params[3] = moments->y;
-    params[4] = (moments->Sx < (1.2 / 2.0)) ? 2.0 : (1.2 / moments->Sx);
-    params[5] = (moments->Sy < (1.2 / 2.0)) ? 2.0 : (1.2 / moments->Sy);
-    params[6] = 0.0;
+    psF32     *PAR     = model->params->data.F32;
+
+    PAR[PM_PAR_SKY]  = moments->Sky;
+    PAR[PM_PAR_I0]   = moments->Peak - moments->Sky;
+    PAR[PM_PAR_XPOS] = moments->x;
+    PAR[PM_PAR_YPOS] = moments->y;
+    PAR[PM_PAR_SXX] = PS_MAX(0.5, moments->Sx);
+    PAR[PM_PAR_SYY] = PS_MAX(0.5, moments->Sy);
+    PAR[PM_PAR_SXY]  = 0.0;
 
     return(true);
 }
 
-psF64 pmModelFlux_PGAUSS(const psVector *params)
+psF64 PM_MODEL_FLUX(const psVector *params)
 {
     float norm, z;
+    psEllipseShape shape;
 
     psF32 *PAR = params->data.F32;
 
-    psF64 A1   = PS_SQR(PAR[4]);
-    psF64 A2   = PS_SQR(PAR[5]);
-    psF64 A3   = PS_SQR(PAR[6]);
-    psF64 Area = 2.0 * M_PI / sqrt(A1*A2 - A3);
+    shape.sx  = PAR[PM_PAR_SXX] / sqrt(2.0);
+    shape.sy  = PAR[PM_PAR_SYY] / sqrt(2.0);
+    shape.sxy = PAR[PM_PAR_SXY] / sqrt(2.0);
+
     // Area is equivalent to 2 pi sigma^2
+    psEllipseAxes axes = psEllipseShapeToAxes (shape);
+    psF64 Area = 2.0 * M_PI * axes.major * axes.minor;
 
     // the area needs to be multiplied by the integral of f(z)
@@ -122,5 +137,5 @@
     norm *= DZ / 3.0;
 
-    psF64 Flux = PAR[1] * Area * norm;
+    psF64 Flux = PAR[PM_PAR_I0] * Area * norm;
 
     return(Flux);
@@ -129,22 +144,32 @@
 // define this function so it never returns Inf or NaN
 // return the radius which yields the requested flux
-psF64 pmModelRadius_PGAUSS  (const psVector *params, psF64 flux)
+psF64 PM_MODEL_RADIUS (const psVector *params, psF64 flux)
 {
     if (flux <= 0)
         return (1.0);
-    if (params->data.F32[1] <= 0)
+    if (params->data.F32[PM_PAR_I0] <= 0)
         return (1.0);
-    if (flux >= params->data.F32[1])
+    if (flux >= params->data.F32[PM_PAR_I0])
         return (1.0);
 
-    psF64 sigma  = sqrt(2.0) * hypot (1.0 / params->data.F32[4], 1.0 / params->data.F32[5]);
-    psF64 radius = sigma * sqrt (2.0 * log(params->data.F32[1] / flux));
-    if (isnan(radius)) {
-        fprintf (stderr, "error in code\n");
-    }
+    psF32 *PAR = params->data.F32;
+
+    shape.sx  = PAR[PM_PAR_SXX] / sqrt(2.0);
+    shape.sy  = PAR[PM_PAR_SYY] / sqrt(2.0);
+    shape.sxy = PAR[PM_PAR_SXY] / sqrt(2.0);
+
+    // this estimates the radius assuming f(z) is roughly exp(-z)
+    psEllipseAxes axes = psEllipseShapeToAxes (shape);
+    psF64 radius = axes.major * sqrt (2.0 * log(params->data.F32[PM_PAR_I0] / flux));
+
+    if (isnan(radius))
+        psAbort ("psphot.model", "error in code: never return invalid radius");
+    if (radius < 0)
+        psAbort ("psphot.model", "error in code: never return invalid radius");
+
     return (radius);
 }
 
-bool pmModelFromPSF_PGAUSS (pmModel *modelPSF, pmModel *modelFLT, pmPSF *psf)
+bool PM_MODEL_FROM_PSF (pmModel *modelPSF, pmModel *modelFLT, pmPSF *psf)
 {
 
@@ -152,17 +177,24 @@
     psF32 *in  = modelFLT->params->data.F32;
 
-    out[0] = in[0];
-    out[1] = in[1];
-    out[2] = in[2];
-    out[3] = in[3];
-
-    for (int i = 4; i < 7; i++) {
-        psPolynomial2D *poly = psf->params->data[i-4];
-        out[i] = psPolynomial2DEval(poly, out[2], out[3]);
+    // we require these two parameters to exist
+    assert (psf->params_NEW->n > PM_PAR_YPOS);
+    assert (psf->params_NEW->n > PM_PAR_XPOS);
+
+    for (int i = 0; i < psf->params_NEW->n; i++) {
+        if (psf->params_NEW->data[i] == NULL) {
+            out[i] = in[i];
+        } else {
+            psPolynomial2D *poly = psf->params_NEW->data[i];
+            out[i] = psPolynomial2DEval(poly, in[PM_PAR_XPOS], in[PM_PAR_YPOS]);
+        }
     }
+
+    // the 2D model for SXY actually fits SXY / (SXX^-2 + SYY^-2); correct here
+    out[PM_PAR_SXY] = pmPSF_SXYtoModel (out);
+
     return(true);
 }
 
-bool pmModelFitStatus_PGAUSS (pmModel *model)
+bool PM_MODEL_FIT_STATUS (pmModel *model)
 {
 
@@ -174,12 +206,12 @@
 
     dP = 0;
-    dP += PS_SQR(dPAR[4] / PAR[4]);
-    dP += PS_SQR(dPAR[5] / PAR[5]);
+    dP += PS_SQR(dPAR[PM_PAR_SXX] / PAR[PM_PAR_SXX]);
+    dP += PS_SQR(dPAR[PM_PAR_SYY] / PAR[PM_PAR_SYY]);
     dP = sqrt (dP);
 
     status = true;
     status &= (dP < 0.5);
-    status &= (PAR[1] > 0);
-    status &= ((dPAR[1]/PAR[1]) < 0.5);
+    status &= (PAR[PM_PAR_I0] > 0);
+    status &= ((dPAR[PM_PAR_I0]/PAR[PM_PAR_I0]) < 0.5);
 
     if (status)
@@ -187,2 +219,10 @@
     return false;
 }
+
+# undef PM_MODEL_FUNC
+# undef PM_MODEL_FLUX
+# undef PM_MODEL_GUESS
+# undef PM_MODEL_LIMITS
+# undef PM_MODEL_RADIUS
+# undef PM_MODEL_FROM_PSF
+# undef PM_MODEL_FIT_STATUS
