Intersecting patches

[Gorf]

Is it bad to have a model where two patches cut through each other?

 

I'm modelling a Harrier GR7, and the fuselage does not taper to the rear, as with most jets, it’s just a cylinder ending in a hemisphere.

 

The tailfin looks like it could be modelled as a single object with the lower part cutting through the fuselage and forming the small ventral fin, for simplicity and reduced splinage.

 

Is this sort of modelling frowned upon? Are there any rendering considerations I need to take into account?

 

The biggest question, though, is that if I should be modelling the whole thing as a single assembly, is there a quick and dirty way of turning the interface between the two patches into a spline?

 

While I’ve got your attention, I’m not happy with the amount of messing about I had to do to integrate the tailfin and the little air vent at its fore base. Was there a better way to do that?

[Stuart Rogers]

Generally there's nothing wrong with intersecting patches - I use them a lot for mechanical objects. They do raise some minor issues, for example...

 

Unless you have modified your patches with displacement maps, the intersection line will be very sharp. Depending upon your requirements, this could be good or bad. Taking yout tail fin as an example - does the real Harrier have a sharp intersection, or is there a raised 'seam' from the weld where the intersecting parts meet? If you decide you do want the fine detail of a seam, you could either (a) create a separate seam patch, which intersects both tail fin and body, or ( add a seam as a displacement map on either the tail fin or body. Creating and lining up the latter might prove tricky.

 

Your graphics card driver *might*, under certain circumstances, render one patch entirely over the other. This has happened to me in the past (in a chor - Shaggy was holding a cup, but the cup appeared to be in front of the fingers that were holding it). I should point out that this is a GFX card problem (which you may not get) and has no bearing on the final render.

[heyvern]

There is a "trick" I use sometimes.

 

On the tail fin where it intersects, add a few extra "extension" rings of splines and create a "curved" sort of "seam edge".

 

Instead of intersecting completely through the fuselage you can sort of nudge it up tight to fit against it. You can even slightly alter those splines to conform against the fuselage section.

 

It doesn't have to be a perfect fit. The tightly curved edge of the fin seam will hid that hard transition.

 

This gives you the benefit of low splinage and avoid that sharp line of intersection.

 

In this case the small ventral fin would be a separate mesh... but the same low splingae.

 

Vernon "!" Zehr