Hi Brian, I don't think there is any great thread on these specific subjects, so this thread here will be it!

Extend is included primarily so there would be a fairly complete set of standard CAD drafting tools. It's a common part of a CAD toolset to have a function to extend a line to match up with another object - in MoI that's extend.

So for example if you have these 2 lines, if you select the first one and run extend, and pick the second one as a boundary, you will get this:



Of course you can get the same thing by drawing a new line and erasing the old one, but if you have to edit complex blueprints with a whole bunch of lines in them, it can save time to have tools like this that save a few steps and also can work on batches of objects.

But unless you're doing drafting you'll probably not need to use it.


> Curve

Do you mean Construct / Curve here ? Right now this includes project which can project a curve on to a surface, and intersect which will calculate the curves of intersection between all the selected objects. Like for instance if you have 2 spheres that punch through each other, you can use Construct / Curve / Isect to create the circle curve where the 2 spheres intersect one another. Sometimes these curves are useful as one step in constructing a complex object.

Network - this is one of the powerful surface creation tools. You know how loft creates a surface through a series of cross sections? Network is kind of like a loft between 2 sets of cross sections simultaneously. It can give you additional control over the surface that is created. Here is one quick example - here is a network of curves:



It's kind of hard to tell from that angle, so here is another angle from the top that shows more of the "network" nature of that arrangement:



So there you can see that these curve are arranged in a kind of 2 directional grid. I've highlighted the curves in one direction there. For network surface, the curves should be arranged in this kind of a 2-directional grid style (although it is ok if they are arranged radially and come together at a point too). Like I mentioned, it's kind of like loft in 2 directions at once, the highlighted curves there are like one loft, and the other set of curves is the other direction loft. But in Network these are combined together into a single surface. So for example in this case that creates this object:



Anyway, that's a very simple example. You basically might use Network when you want more control over the created surface than just a loft gives.


Offset - offset works on either curves or surfaces, you might use it on curves to create a curve setup that has equidistant properties, like here for example is one curve and its offset forming an outline for a thick wall. There are different ways to create thickness, like you can use shell if you want to, but sometimes it is useful to do the more low-level offset approach to make individual parts:




Blend - blend is about creating a smooth pieces in the empty space between the ends of 2 existing parts. You can use it on curves or surfaces. Here's a curve example:



Starting with those 2 curves that have a space between them, selecting them near those ends and running blend created a new 3rd curve that connects between them smoothly.

Here's blend on surfaces - 2 surfaces with some space in between them, select the 2 edges and blend calculates a new 3rd surface that is smooth between them:



Hope this helps, let me know if you need any more info on any of these.

- Michael

Sorry you had to go to all that trouble. Terminology (nomenclature) is I think the main problem.

At least two items have completel different names to me--connect/bridge. Network, is that catmul/clarke or something?

Anyway will now work through those.

<Network, is that catmul/clarke or something?
I believe that you can compare with "Coons" if you have only 4 or 3 curves or "Gordon's" surfaces/curves" if you have more than 4 curves :)

Welp, as much as I use MOI, I'm still learning stuff also! (Never used extend before - boy is it handy though!)

Brian, you'll enjoy network once you get the hang of it - it's a great tool too have when you want to really define how your surfaces look! I was so glad to see it put in!

-Will

Hi Brian, yes Pilou has the other technical terms for Network there.

Catmull/Clark is the name of the algorithm used by polygon subdivision surface modelers to produce a smoothed down subdivided surface from an initial coarser polygon cage: http://en.wikipedia.org/wiki/Catmull-Clark_subdivision_surface

- Michael

Yes I meant Gordons--I was just too lazy to look up the name correctly. Thanks.

Offset seems to be creating some understanding difficulties. See attaced.

I though I would, in effect, get a duplicate in a new location sort of thing. I guess I need better education please.

Hi Brian, for an actual duplicate you would use something else, like Transform / Copy, Array, Ctrl+Drag, or copy/paste.

Offset creates a new curve or surface that is a given distance away from an existing one. It kind of traces an outline that is a distance away, it is not the same thing as a duplicate.

Here is another example - given this starting curve:



Doing an offset of distance 3, clicking to the top side (you can pick which side to offset to), will generate this:




The second curve is not an exact duplicate of the first, it is basically a parallel result, with extensions for corners.

You use it for things where you want parallel curves or surfaces that form a particular thickness between the 2 parallel pieces. You can't normally make a parallel curve by just an exact duplication except for the case of a simple line segment.

Let me know if that doesn't answer your question, that is more about the actual output of Offset, the workflow for using it has a couple of different modes you can set, like through point mode or given distance mode.

- Michael

Michael--but my offsets bear little, if any, visual relationships to the original? And more--

Hi Brian, on your first example, you've got a 5-sided polygon and the outside offset is 5 sided with rounded corners, and the inner one has 5 lines.

5 components in each thing, I'm not sure why you don't consider these to be related?

It looks like the differences in this case from what you are expecting are due to some of the options that you've changed - when you set Corners : Round you'll get rounded areas on corner extensions. If you set this to the default "sharp", then the larger shape would also be a straight-edged 5-sided polygon closer in resemblance to the original.

Also, you've unchecked the "Trim" option - that's why the inside one is made up of 5 overlapping lines. If you turn Trim on then the inside one would also be another 5-sided polygon as well.


On your second example, you've got something with tight bends in it, and your offset distance is a lot bigger than the curvature of the bend - this would create an offset that loops back around on itself with curly-cue type things, but with Trim turned on it will try and remove the loops. Sometimes MoI will get confused with this type of offset and you might not get the portion that you need - that's why there is a Trim option that you can turn off so that you can get the entire piece with curly-cues if you want which can then be cleaned up.


Try it with the default settings on your polygon (corners: sharp, and trim on), and with a much smaller distance with your one with the tight bends, and the results should be easier to understand I think.

- Michael

Hi Brian, here is another example to show you what happens in the case when you've got a tight bend in a curve and you ask for an offset distance greater than the curvature of the bend:



This tends to be easier to understand when you see it happening in small steps. Here are a sequence of 6 different offsets, each one slightly larger in size.

You can see that the first 3 everything is pretty simple, the distance involved is less than the curvature of the bendy part.

But after that you can see that portions of the offsets from either side of the bend start to overlap one another - this makes that kind of "curly cue" situation that I was describing previously (the results shown here were with the Trim option turned off). If there are a large number of these, it is not unusual for the offseter to get confused about which parts are the "main" parts and which parts are the loop parts to throw out, that's what happens when you get a small result curve from a complex offset. But you can turn off Trim to get back some raw results that you can then edit by manual trimming to get the final result.

You might experiment more with offset initially using the "Through pt" mode instead of a specific distance, the through point mode makes it easier to see how the offset shape changes as you move gradually away from the curve in small steps.

- Michael

Michael,

If you ever decide to give up on coding, I suggest you get a job teaching!

Thanks for all the great examples and explanations. They clarified a lot for me.

that was a great explanation thank michael , simple enough that even I could understand it!

I have spent more time trying to get to grips with "Offset".

I have come to the idea that both for solids and lines this is an unnecessary and maybe confusing "extra"

"Cut and paste" and "scale" seem to be more "reliable" alternatives?

(Or am I missing something?)

Hi Brian, just plain scaling does not do the same job except for special cases like a circle.

Here's an example (.3dm also attached):



There isn't any way just through scaling to create a parallel curve a constant distance away from that one, give it a try.

Here's another example:



Here you can see how the lines of the offset are of different proportions with one another. Scaling will not produce this result.

- Michael

Thanks Michael. It just seems that there is less "logicallity" in offset.

Well--maybe different illogicallity in both options??

How are made the offset?
Seems easy in 2D but in 3D?
Extremities control the result for have a sort of perpandicular form between them?

Hi Pilou, the offset is created by a kind of "tracing" procedure that marches along the curve and displaces a point sampled from the curve by the given distance.

You can do it on a 3D curve, but the displacement direction will happen relative to a plane. It tends to be more predictable when you do it just on planar curves.

- Michael

Hi Brian, I don't really have any ideas on how to make it more logical...

I mean right now the basic procedure goes like this:

Step 1 - select a curve:



Step 2 - click on Construct / Offset to launch the offset command.

Step 3 - click a little distance away from the curve to create a parallel one going through the point where your mouse is at:



That's all that you do to create a basic parallel curve... It can get more complex if you want to tweak various options or work with more complex curves, but I can't really think how to get more logical steps than that for the simple basic case...

Is there anything that you can pinpoint here that doesn't seem logical?

- Michael