Parametric is not the same as History-Based
The risk of using a lot of buzzwords is that eventually the words begin to have no meaning at all. One of the words that gets thrown around a lot is the word “parametric”. I wind up writing an article like this, or at least complaining about the public mis-use of the word every couple of years, and you guys probably get sick of hearing me complain. After all, it’s the people who don’t read this blog that are likely the worst offenders.
To be honest, I don’t even really want to complain about what the word means, I mainly want to complain about what it doesn’t mean.
Too often when a part or an assembly changes someone says “oh, that’s parametric change”. And when you start talking about direct edit, someone inevitably says, “yeah, but I like parametric modeling”, as if it’s something different.
Here’s the thing. When a lot of people say “parametric”, they really mean “history-based”, or maybe “sketch/feature based”. They might even mean “associative”, which generally means links between files. Parametric, as we are all sick of hearing, is when you use a parameter to drive geometric change in a model. A parameter could be a number, or maybe even a check box. It’s a dimension, or a number of pattern instances, or an option, or something in a dialog box. It is not necessarily anything that has anything to do with history-based changes, like reordering, or links between files in an assembly.
Parametrics can be driven by equations, tables, excel, direct input, etc.
And here’s the thing that blows history-based users minds – Synchronous Technology (direct edit suited up with a lot of additional tools) is parametric. You can make changes using equations, tables, dialog boxes, dragging, you name it. One of the best things about ST is that you determine at the time you make the change what the design intent is. You don’t have to create it, then try to remember what you did 6 months ago. One of my favorite things is that you can change which end of a dimension moves by selecting one side of the dimension or the other. In fact, you determine at the time you make the change which faces will be involved in a change, and those faces don’t have to line up with the features you used to create the model. Whatever you select is what the change will apply to.
If you want to characterize what’s different between SW and ST, the big difference is that SW is history-only. ST allows history and direct. They are all parametric.
So please, when you’re referring to stuff that includes direct edit tools, don’t call them non-parametric. Call them history-free.
Yup Fusion 360 has some intelligent Direct Modeling tools built in. For example if you “Press/Pull” a fillet it can actually change the original radius value. You can also use it and have a feature in a timeline of a “direct” tool. Fusion gives some flexibility to how you want to “record” or “not-record” history, make “base features” etc.
Definitely agree with you on terms here.
Good blog post. “ST allows history and direct.” So does Fusion 360, gotta try it Matt, really. I’m looking forward to your comments on F360, and I’m guessing a couple of hundred other people are too. 🙂
Just for the heck of it I once did a file in SE and exported it as an .xt file where it was opened up in SE and a friends copy of SW a few years back. The immediate thing to notice was that I could do what I wanted in SE with edits and I don’t remember the specifics but my buddy had trouble doing the same. But what was an eye opener was the ever increasing pile of history data added to the SW file each time compared to the SE file which reflected only the new features which could add or subtract from the total data size. SW grew and grew and grew and added considerable data to be considered under the hood. Inventor is so bad compared to SE that I never used it for modeling in the three years I had a full seat of it so I have no idea what it would do with data but I suspect nothing good. Taking the same edit and doing and undoing it caused SW to grow each time and SE varied hardly at all. Creating and then removing features and SW faithfully added them all and once again SE changed in size only to reflect the increase or decrease of geometry complexity and not every single thing every single time in a cumulative fashion like SW did.
The ability to click on a dimension and assign how they relate to other faces or to the center is a powerful tool I use all the time. I remember having a discussion with an Autodesk Inventor guy who was puzzled about direct editing and thought all flavors were the same. The big difference I had to explain to him was the assignable intelligence Synchronous brings to the table.
There may be a number of parametric modelers by your correct definition but only one brings a complete professional roll around direct editing tool box with it’s presence. I am sure NX does the same but I don’t like to talk about or use Brand (N)X ;D
Have a good 4th Matt and nice to see you back and writing on a regular basis again.