find equation of model's surface or equation of datum curve

Hello, I have a mold that I created in ProE (not using the manufacturing "mold cavity" option, this is just a PART file. This mold is used to create a rubber model that looks like two hills with a valley in between on top of an elliptical disk (problem uploading image) My issue is that I want to find the exact equation of the surface of the model. Note: this means finding the equation of the indented surface of the "mold". Is there a way that this can be done in ProE? Or maybe, is there a way to extract the equation of a datum curve given that it wasn't created with an imported equation? Any help would be great. (If ProE knows the location of the contours, created by cross-sections, doesn't it know the location of the surface? I've tried picking plenty of points along the contours (datum curves) and fitting a polynomial through them (for each contour) but this is still not the exact equation of the contours. It seems like I should be able to click a surface, define some boundary (ellipse) and ProE will spit out an equation of that surface.)
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