Please see the following compilation. I always thought it was important to understand the following reality once I first learned about it many years ago:
Unfortunately, it’s very difficult to get newusers to understand this, no matter how many times I reiterate it to them.
So, this is good now cause I’m focused on bringing this to attention, and may reference this in the future or create a new thread or find a current more appropriate thread if this one isn’t appropriate.
Why is it most newusers can’t get it through their head that " Whenever a NURBS surface is shaded or rendered, the surface first converts into a polygon mesh."?
I think it’s because most users don’t care about the details, cause they just want to be users.
Bear with me as I get to my main point.
As newbs(newusers) or rather ‘users’ that just want to be users and don’t care about the scientific details behind all of Rhino’s characteristics, these ‘users’ completely disregard ‘mesh properties’ and in most cases disregard file tolerance.
In fact, most of the time if not all of the time these ‘users’ will just use default settings everywhere.
Therefore, as these newbs go forward throughout their work, they will model and propagate errors through bad habits caused from this said ignorance.
As these particular users model they use what they ‘see’ and snap to those ‘edges’ and ‘vertices’.
Over time, they can end up with problematic models that will only join into a ‘closed’ manner under higher and higher ‘file tolerances’.
Hence, as ‘edges’ get pulled away from ‘original 3D surface edges’, these particular users will end up chasing their own tail per say. They will be fighting for ‘vertices’ to be ‘coincident’ – truly.
They wont even realize they’re relying on a so-called ‘render mesh’ to visualize where vertices are and edges are – without understanding they’re seeing a mesh and snapping to edges that aren’t ‘original’ or true.
Instead, they’re falling victim to chasing around these edges and vertices that are ever changing as they go forward changing their models and trying to succeed with compounding errors.
The more the tolerance, the more the ‘pulling away from original’, the more the compounding error over time.
Have you ever seen a newb try to make a model where there’s 4 or more surface vertices that need to be coincident to 0.0005" but they can’t do it? And one moment they think they got it, and another where they don’t?
To overcome the mystery of this problem I have derived the following sequence over the years, in order to more quickly analyze a newbs geometry and see exactly where the ‘true’ problems are.
<><><><><><><><
1.) selpolysrf
2.) explode
3.) refresh shade
4.) rebuild edges <1xe-05>
5.) refresh shade
6.) join
7.) show edges
<><<><><><><><><
Then if, under file tolerance of say 0.0005", there’s any naked edges – I’ll see the true problem areas and address them accordingly if necessary.
Sometimes yes you can just cheat and do things like switch the file tolerance to 0.001" or 0.01" and join everything – ignoring the fact you’re letting edges and vertices getting yanked away from originals.
But that’s bad habit – imo.
I prefer to model with a strict tolerance of 0.0001", but over the years I’ve become dampened to allow 0.0005", and on occasion 0.001".
Still, under a tolerance of 0.001" a user should follow good habits, and understand the underlying nature of Rhino’s characteristics. But sadly, some users don’t care to pay attention to what’s happening behind the scenes such as “Joined and exploded polysurface Edges are pulled away from the surface” – for example, along with " Whenever a NURBS surface is shaded or rendered, the surface first converts into a polygon mesh" – to reiterate another example.
Now on to challenge your claim further, I’ll focus for a moment on a common thing newbs do, associated with using default mesh properties:
And follow it up with the following:
Point here being is there certainly is an entangled effect of a user persisting to model with bad tolerances and bad mesh properties.
Because usually if not always, “water tightness” should be the end result in the 3D modeling realm.
In modern times yes 3D printing slicer programs etc. may have ways to patch things and fix “errors”, or CAM programs can ‘stich’ or ignore solids or lack thereof.
But a nice clean accurate truly solid and water tight .step model is ideal as an origin for most work – imo.
So, I often will encourage ‘users’ to follow the mesh settings I prefer in most cases, shown in the following:
