A blended ISDX surface needs 2 or more disconnected curves to define a single direction for the surface (i.e. all primary curves, no cross curves). This is like a 'loft' in other packages (like Rhino).
A boundary surface needs 4 (you can have 3 but that is unadvisable) connected curves to define both directions for the surface.
The both have their plusses and minuses, but a boundary surface typically gives you more control, whereas a blended surface is sometimes easier to deal with.
The blended surface is more like a 1 or 2 rail sweep... Create 1 or 2 'rail curves', and then only as many curves as necessary to define the section (tip: less is more.. too many xsec curves make for 'wavy' surfaces). These curves should be connected to the rail curve .
Then, create a new surface, select the 2 rail curves and hit 'ok'.. Then hit 'cross curves' and select the xsec curves, and complete the surface.
A good practice for the blended surface is to create the xsec curves using a datum normal to one of the rails (aka Radial Plane). After you have made the rail curves, create a new curve and designate it as planar. Open up the 'Refs' tab and press the arrow button next to the word Reference. Select one of the rail curves as the reference and it will change the plane type to 'Radial Plane'. You can adjust the length parameter to put the plane at the correct location along the rail. This ensures that the section curves that you are creating is always a true representation of the section (at least in relation to the rail curve that you are using).
Has anyone tried ISDX in Wildfire 3? I am interested in finding out how well the "primitives" tool works... Apparently now you can create simple curve shapes (arcs, circles, polygons) inside the ISDX environment. My preproduction release isn't licensed for that, for some reason..
