Hi,
I'm getting close to something that I like EXCEPT ... when I loft this model I loose the profile and the surface looks like it has stretch marks along the sides. The surface quality gets worse as you go toward the back. Also I can't sweep it, something funny happens at the front.
I like what I get with loft and think that may be the way (except for the problems) but at this point I really don't know.

Thanks for your time.

bz

Hi bz, those stretch marks look like just a display artifact from slightly long and skinny triangles in the display mesh, it looks like your actual surface is fine.

To really see more of the true surface, try doing an export to a polygon mesh format like OBJ for example, then crank the slider over to the right and also if you have things that are long but only slightly curved, putting in a distance value for "Divide larger than" can also be good as well to make sure the polygons are dense enough that you're not seeing polygonalization artifacts alone.

Like in your case here I exported to OBJ and cranked the slider all the way to the right (the slider controls the "angle" parameter), and also put in "divide larger than" = 2, and that makes the polygon representation nice and highly diced up so you won't see what are called "mach banding" artifacts that are associated with trying to make somewhat rough polygon structure look as if they are smooth.

When I do the OBJ export (which you can just cancel if you were only wanting to examine the overall true surface quality) with those settings, in the mesh preview that you see on screen you should see those "stretch marks" are not there anymore:



If you do go to export this object to a rendering program, you will also probably want to put in some amount of "Divide larger than" at that time as well, when polygons are long and skinny it can tend to make shading artifacts spread across a sort of larger area and thus become more noticeable. When things are diced up only by angular measurements alone (which is the case for the in-viewport display mesh) then a semi-tubular shape like this that is only gradually curved in one direction but tightly curved in the other tends to get long skinny triangles since the long gradually curved region does not end up with very many divisions in it. That's what putting in "Divide larger than" can correct, it forces divisions based on length rather than just on angular deviation of surface normals.

- Michael

Also since I'm fairly often doing this type of surface quality analysis by doing a "dummy" mesh export, I have a shortcut key set up for it, like this:

Key	Command
Space	SaveAs c:\temp\test.obj

With that shortcut key set up under Options > Shortcut keys, you can then push the Space bar and that will trigger a mesh file save out to OBJ format without you needing to put in any filename for it like a regular export. Then after you're done examining how the surface looks when it's finely diced up you cancel out from that rather than actually writing the test.obj file.


After a while you get kind of more used to the types of problems that are actually more just related to display glitches rather than problems in the real surface itself.


There are certain kinds of shapes as like you've got here with only gradual or shallow curvature in one direction which tend to have the most kinds of display problems.

Another thing is the display mesher has a big focus on generating things quickly so that you don't have to wait around all the time every time you do some editing operation on a model.

- Michael

Hi Michael,
Thanks for the GREAT advise !
I tried the export and see what you mean.
One thing I can't tell is if the solid is true to my upper profile line. In Moi it doesn't look like it is but in OBJ I can't see the line. Is it there and I just can't see it ?

Thanks again.



bz

Hi bz,

> One thing I can't tell is if the solid is true to my upper profile line. In Moi it doesn't look like it is
> but in OBJ I can't see the line. Is it there and I just can't see it ?

OBJ export does not do anything with curves, so you won't see them using that method for visualizing things.

But you can do something like set up the shortcut key as described above, then zoom in a bit to the area where you want to examine, then push the shortcut key and if you don't see a big shift in the silhouette of the shaded surface then you can tell that what you're seeing on the realtime display is what is really there.

Typically in the regular display you would see some amount of angularity as a display glitch due to a light display mesh, but that looks like a type of polyline where some points are on the true surface and you're seeing some straight line connections between them. Basically you wouldn't see a really major deviation from the true surface without seeing a lot of straight edged parts to the shaded display.

Since you don't see that in your case here you can tell that the surface really does not follow along to your midline upper profile - that's probably because you are using "loose" loft which works like that, it tends to make a surface that is somewhat shrunken down from the profiles instead of going directly through them but at the same time tends to make a smoother result with less wiggles and undulations in it.

If you want to make a loose loft that comes closer to that side profile, you would need to make the sections a bit larger than the profile rather than sitting right along it.

- Michael

Very Cool !!

Thanks.


bz