Hey Michael,

Thanks for the feedback, I'll try the image snapping ASAP. I think what I basically need to know is if it would be more of an advantage to do this kind of modeling in MOI instead of my regular sub-d modeler. I've actually modeled about 60% of this car already, and just wanted to know if I could do it with greater accuracy using MOI.

I'm attaching the .3dm file to this post, but Im not sure if MOI packs the background images as well, so I suppose I should upload those too.

Anyway, if you could be kind enough to give me a quick runthrough of how to tackle the bonnet, I'll be able to figure out how to model the rest of the car. Then I can establish if MOI is the best solution for this kind of modeling. (which I hope it is btw, Im having a blast so far)

anyway, thank you.

Hi,

> but Im not sure if MOI packs the background images as well,

It doesn't, so thanks for including them.


So the background image snapping that I described won't help you in this case, it looks like you've already got the image perfectly centered because you snapped it to the grid. The problem here appears that the drawing itself is not centered within the bitmap image.

Instead of snapping on to a corner of the image, you can also just drag on the image to shift it around a little bit - so to center this one you want to zoom in to some reference area like the hood ornament, and then go to View/Image, and then click and drag on the image and shift it left or right until it looks more centered.


You'll need to approach the curve drawing slightly differently too - there you've got your curves as a bunch of line segments. That is going to be hard to surface with a smooth surface patch, you're going to want to draw smooth curves there instead. This is a lot different than the Sub-D style, things don't get smoothed down from a set of facets, instead with NURBS modeling you more construct smooth surfaces directly from smooth curves. Faceted curves will give you faceted surfaces.

I'll give you some details and examples tomorrow...

- Michael

Hi, here is one way to do this part.

I'd say probably the single biggest tip for this style of thing is not to try to model little cuts in the surface in the initial surface patching phase. If there is something that looks like a sharp cut in a flowing surface, try to model the extended flowing surface in one piece first, and then use trim to do the sharp cuts after the surface is created.

Otherwise if you try to include a sharp cut curve as part of your initial skin, it interrupts the topology and it will be difficult to get a smooth surfacing result - your surface will tend to bunch up or have creases in it when your input curves have creases in it.

So a quick overview of what I did (let me know if you need more details on any particular part).

First I went to View/Image to edit the position of top background image. I zoomed in to the hood ornament and clicked and dragged on the image horizontally (make sure Straight snap is on) until it was centered better.

Then I traced some new curves to follow the outline of the hood, including the center line. You previously didn't have the centerline, but I think you'll want that so you can make sure the center of the hood is shaped so the profile is correct.

To draw the curves, I used Draw curve / Freeform / Control points. Generally this should be the tool to prefer when tracing curves to surface later. I went along and placed points to guide the curve along the bitmap contours. Most of the time you place the points pretty much right on the contour, but since the actual curve is a slight bit shrunken down from the control point "hull", sometimes you may place a point slightly off of the contour so that the curve itself will be traveling on the contour. This gets more natural after you practice it for a bit. Try to make fairly regularly spaced points. Also try not to make the points wiggle around - I mean as you trace a curve, make sure each point is progressively slightly further over, avoid having any kind of unnecessary zig-zags in the point placement, even small ones. That's important to help avoid making lumps and bumps later on.

Oh, also for curves you intend to mirror pay attention to the first inside point, the direction of the end point and the first inside point define the tangent direction of the end of the curve. If you want to mirror the curve later on you want it to be smooth, so that means the tangent direction should be exactly perpendicular to the mirror axis. So for instance if you are going to mirror around the Y axis, you want to make sure the first and second point of the curve are lined up right along the x axis direction.

Ok, so I did all of that in the top view to get the initial curves. Then I switched to the side view and dragged points vertically (in the z direction) to shape them from that view as well, sometimes adding some points when necessary.

The part that is a bit tricky is for the corner - instead of tracing a short, sharp curve for the corner nearby the headlights, I instead drew the curves following a kind of imaginary extension path. Otherwise this is where having a short suddenly sharp curve would make it hard to surface with a nice smooth piece.

Let's see - then I mirrored those 3 pieces over, joined the top and bottom 2 pieces into single larger curves, and then this is ready to surface. In this case it worked best to use the Network command, select all the pieces (make sure the top and bottom ones that were halves are joined into a each a single longer curve).

Then to get the corner shape, I traced that little piece in the top view, make it overshoot a bit so that it will divide the surface where it intersects, then it is not necessary to move that using the other view, just use Trim and use that as a cutting piece, and it will get projected on to the surface. (Hmmm, looking at it now from the side view, the projection straight up wasn't quite the right shape, so this would need some tweaking).

And that's how that hood was built.

You could probably get a better quality surface with some additional control over it if you also did a kind of "imaginary extension" of the center line up towards the top so that the the surface was sort of more regular around the windshield area. Right now having those shapes that go towards sharp points have some side effects on the surfacing - sort of the sharp point tries to blend together to the other curves. If you again did a more extended surface that had more of a regular end to it instead of that sharp point, it would make a more predictable and even surface, and then you would trim out the windshield part.

Hope this helps some!

- Michael