>> Sketckup is a lot of fun, 
> 
> Can it export stuff POV-Ray can use?

It can export data as some kind of XML format. (Apparently it's an open 
standard - I don't know how well documented!) If you wrote a converter, 
then... supposably.

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>> welcome to 3D visual modelling! :D
> 
> *That* is what I want Minority Report gloves for! :-)

Ah, Minority Report. How often does a film come along that makes 
everybody want a particular fictional technology?

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>> ...you need to get a proper 3D CAD program? :-)
>
> Yeah, figures.

Most CAD programs I've used store a tree of features/actions used to get to 
the final shape, this means you can go back and edit any of those previous 
steps.  In your example the shape you drew to make the hole is stored 
exactly as that in the file, then of course you can edit it and see the 
result.  I saw partly this kind of behaviour in 3D Studio Max (or whatever 
it's called now), in that you could keep two separate objects and see the 
intersection of them, but most mesh editors just store the mesh and no extra 
data.

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> Most CAD programs I've used store a tree of features/actions used to get 
> to the final shape, this means you can go back and edit any of those 
> previous steps.

That sounds like a more logical way to work.

Presumably CAD also allows you to do things like "find a point 3/5 along 
the length of this edge". SketchUp automatically marks the 1/2 point for 
you, but for any other point you've got to get out a calculator.

Other annoying SketchUp features include the lack of the ability to 
manipulate a circle be its center. (Because, of course, once you've 
created it, it's not a circle any more. It's 24 unrelated edges.) And 
the best feature of all is the way surfaces "stick" to each other as 
soon as they touch...

> I saw partly this kind of behaviour in 3D Studio Max 
> (or whatever it's called now), in that you could keep two separate 
> objects and see the intersection of them, but most mesh editors just 
> store the mesh and no extra data.

Yeah. How SketchUp does intersection is that you line up the two 
objects, press "intersect", and then delete the geometry you don't want. 
Manually. Which, for curved surfaces, takes a really long time. 
(Because, naturally, those surfaces aren't really curved. Stupid 
idea...) Also, you can't delete any item smaller than a certain size on 
screen. You have to zoom in first. And the minimum size is significantly 
larger than you'd expect.

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> Presumably CAD also allows you to do things like "find a point 3/5 along 
> the length of this edge".

AFAIK there is not usually any automatic way to do that, you'd just need to 
add a formula to one of the point dimensions that says something like 
"Edge1.Length * 3/5".  That way, whenever the length of that edge changes, 
the point is always fixed 3/5 of the way along.  You could then draw some 
geometry referenced to that point, then of course that would all move with 
the point too.  It gets a bit like POV, where you can just define a variable 
for something like "screw position", and then drive lots of other features 
like holes and cut-outs in lots of parts from that one variable.  The 
benefit of this is when your customer says "ok we need that screw moved 
1.2mm" it only takes you a few seconds to update all your parts rather than 
an hour or two.

> the best feature of all is the way surfaces "stick" to each other as soon 
> as they touch...
...
> Also, you can't delete any item smaller than a certain size on screen. You 
> have to zoom in first. And the minimum size is significantly larger than 
> you'd expect.

I would expect there would be settings for these sorts of things?

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>> Presumably CAD also allows you to do things like "find a point 3/5 
>> along the length of this edge".
> 
> AFAIK there is not usually any automatic way to do that, you'd just need 
> to add a formula to one of the point dimensions that says something like 
> "Edge1.Length * 3/5".  That way, whenever the length of that edge 
> changes, the point is always fixed 3/5 of the way along.

Right.

> You could then 
> draw some geometry referenced to that point, then of course that would 
> all move with the point too.  It gets a bit like POV, where you can just 
> define a variable for something like "screw position", and then drive 
> lots of other features like holes and cut-outs in lots of parts from 
> that one variable.  The benefit of this is when your customer says "ok 
> we need that screw moved 1.2mm" it only takes you a few seconds to 
> update all your parts rather than an hour or two.

SketchUp allows you to draw precise sizes easily, and it allows you to 
line things up easily. What it does not do is allow you to "link" things 
so that when something changes, other things change to match. You'd have 
to propogate any necessarily changes manually yourself. SketchUp makes 
it quite easy to adjust everything by exactly the right amount, but you 
still have to know what to adjust and how to adjust it.

>> the best feature of all is the way surfaces "stick" to each other as 
>> soon as they touch...
> ...
>> Also, you can't delete any item smaller than a certain size on screen. 
>> You have to zoom in first. And the minimum size is significantly 
>> larger than you'd expect.
> 
> I would expect there would be settings for these sorts of things?

The delete size, maybe. (I haven't found the setting anywhere though. 
There are surprisingly few settings you can adjust.) The sticking 
appears to be a design feature - annoying as it is. (You can prevent it 
by using layers or grouping surfaces into seperate entities.)

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>> Now, sure, if your window is rectangular, the push/pull tool makes it 
>> easy enough to continue. But what if you made a *circular* window? Or 
>> some even more complex shape?...
> 
> ...you need to get a proper 3D CAD program? :-)

On the other hand, weren't you the guy complaining that "propper 3D CAD 
programs" are too crash-happy? At least SketchUp is reliable. ;-)

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> On the other hand, weren't you the guy complaining that "propper 3D CAD 
> programs" are too crash-happy?

Not me, I can't remember the last time Catia crashed on me.  Don't ask me 
about the thermal simulation software I use though...

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Invisible wrote:
> Yeah. How SketchUp does intersection is that you line up the two 
> objects, press "intersect", and then delete the geometry you don't want. 

Blender too.  I usually move the original forms to another hidden layer.

> Manually. Which, for curved surfaces, takes a really long time. 
> (Because, naturally, those surfaces aren't really curved. Stupid 
> idea...)

What makes you think really curved surfaces would be faster?

BTW, if you want curved surfaces, subdivision surfaces is the way to go 
(no idea if Sketchup handles them).  That way, you may keep and handle 
operations on very simple "cage" mesh while having a very "curved" final 
surface... I'm guessing intersecting between 2 "low-poly" cage meshes is 
way faster than between 2 high-poly ones.  You intersect 2 low-poly 
cages and give the resulting mesh a subdivision "modifier"...

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>> Yeah. How SketchUp does intersection is that you line up the two 
>> objects, press "intersect", and then delete the geometry you don't want. 
> 
> Blender too.  I usually move the original forms to another hidden layer.

Well, it does mean that you have one "intersect" operator rather than a 
seperate union, intersection and difference. But for complicated meshes, 
it takes forever...

>> Manually. Which, for curved surfaces, takes a really long time. 
>> (Because, naturally, those surfaces aren't really curved. Stupid idea...)
> 
> What makes you think really curved surfaces would be faster?

Treating a curve as one edge, rather than 25,000 edges, makes it far 
faster for a human to work on. (I make no claims about how easy or hard 
it is for the computer to work with.)

> BTW, if you want curved surfaces, subdivision surfaces is the way to go 
> (no idea if Sketchup handles them).

Nope. SketchUp handles only straight lines. The whole program is 
optimised for working with geometry with lots of lines in it. If you 
want fluid, organic shapes, SketchUp is a very bad choice.

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