35 Replies Latest reply on Aug 22, 2018 11:03 AM by Roland Schwarz

# Parametric?........ What do you understand it to be?

Hi all,

Please don't go and use google, Wikipedia and the likes for generic answers, I'm actually interested in what your honest and at the moment understanding of "Parametric" is.

Dave.

• ###### Re: Parametric?........ What do you understand it to be?

I define parametric as the dynamic relationship between the part's definition of its geometry with its surroundings (constraints) and dimensions such that if the surrounding geometry or the part's dimensions change then the particular geometry updates accordingly.  ACAD is not parametric by my definition.  A part with a hole diameter that is constrained to be in the center of the part or that is setup to have a diameter one-third of the part width is parametric since changing the part affects the hole per the design intent.  Parametric is the key enabler of Design Intent in my book.

• ###### Re: Parametric?........ What do you understand it to be?

My first impression was, give a numeric value to a form/distance and this measure will be arranged any other chain of measure. Mechanical Desktop was my first tool who can give me something like this.

• ###### Re: Parametric?........ What do you understand it to be?

Parametric, define size using parameters instead of a constant.

Dimensions were constant.  Once you gave it an value, you need to delete it to give it a new one.

With parameter, dimensions can change.

Even better dimension can use equation.  Dimension can be related to other dimension.

• ###### Re: Parametric?........ What do you understand it to be?

Parametric = Design Ballet

• ###### Re: Parametric?........ What do you understand it to be?

Being the simple-minded guy I am, to me it's as basic as I change something in one place it updates somewhere else.

• ###### Re: Parametric?........ What do you understand it to be?

... and this is why I use the "actual" sketch dimensions where possible.

Steve C

• ###### Re: Parametric?........ What do you understand it to be?

Relationship controlled design.

An assembly can be as fluid as water or as solid as stone.

I have done design table heavy builds and builds where each individual part is fully defined prior to being put into an assembly.

I prefer a mixture of both and to me that is parametric modelling, the freedom to choose how I want to design and the tool to get there. Also changes applied at assembly level transfer throughout parts, drawings etc.

• ###### Re: Parametric?........ What do you understand it to be?

Parametric to me means that whatever the item is that is parametric will update as needed without additional user input.

Example:  My drawing title block note is linked to the part's custom property named "Part Number".  When I change the part number of the part, the drawing updates without additional input from me (other than a rebuild).  The Drawing note is parametric, while the part number custom property is not.

Another one:  The length of my part is driven by a dimension that is equal to (linked to) global variable A.   Global variable A is an equation which states, "Global Variable B/3"

Therefore, the length of my part, the dimension controlling it, and Global Variable A are all parametric.....but Global Variable B is not.

• ###### Re: Parametric?........ What do you understand it to be?

Parameter driven, interconnected, interrelated, dynamic, relational.

• ###### Re: Parametric?........ What do you understand it to be?

Parametric means that the model is defined by parameters rather than the position of its geometric entities.  Those parameters may be easily changed or adjusted to drive the positions of the geometric entities such that design intent may be followed.

Just curious... What is your reason for asking?  Is someone else defining it in a way that doesn't match your understanding of the term?

• ###### Re: Parametric?........ What do you understand it to be?

Parametric means that the model is defined by parameters rather than the position of its geometric entities. Those parameters may be easily changed or adjusted to drive the positions of the geometric entities such that design intent may be followed.

Just curious... What is your reason for asking? Is someone else defining it in a way that doesn't match your understanding of the term?

Hi Josh,

My reason for asking is that although I had a semi-grasp of what it meant I couldn't actually find the words to explain it to someone a couple of days ago. Doing the google thing mainly gave me highly convoluted ways of explaining it so I've turned to the professionals for all the different views of how they interpret it. There are some great and yet simple explanations of it here now. I like the KISS theory.....

Dave.

• ###### Re: Parametric?........ What do you understand it to be?

Dave

For me, in terms of CAD, a model having excellent parametric qualities can take a change to its initial features and yield the expected result with no errors. A model with good parametric qualities will throw some errors that need to be addressed but has no hidden flaws. The typical paranormal model I get from "others" will blow up entirely, contains surprises out of sight, and needs to be remade from scratch.

Dwight

• ###### Re: Parametric?........ What do you understand it to be?

Dwight Livingston wrote:

Dave

For me, in terms of CAD, a model having excellent parametric qualities can take a change to its initial features and yield the expected result with no errors. A model with good parametric qualities will throw some errors that need to be addressed but has no hidden flaws. The typical paranormal model I get from "others" will blow up entirely, contains surprises out of sight, and needs to be remade from scratch.

Dwight

Dwight, you caught my eye with that one!

• ###### Re: Parametric?........ What do you understand it to be?

Very well put Dwight!

• ###### Re: Parametric?........ What do you understand it to be?

All things modeled working together as intended, in the 3d graphics of the pc.  It is only as smart as the guy modeling the parts and assembly as there are some of us that can make parts grow when one part changes and others of us that must then update each part as one part changes.

edit.....

The cool thing is that once you have a drawing made for the part is that the drawing will update too.  Depending on company procedures the drawing dimensions changes could impact the part.

• ###### Re: Parametric?........ What do you understand it to be?

In an effort to keep it simple... To me it's any automation of adjusting the parameters of your geometry. Which is  the mindset to any piece of tooling I draw. I don't think at all about making it simple for me to create but instead how easy is it going to be for someone else to use my print and model (and assembly) to create a new part of similar geometry but different dimensions. This is the whole reason behind us going to 3D CAD software instead of sticking with AutoCAD. For others that do one of a kind models this doesn't hold true but our tooling is always so similar in shape it doesn't make sense to do it any other way. Have a great day and a HUGE welcome back to my good friend Dave Bear!

• ###### Re: Parametric?........ What do you understand it to be?

Certain parameters of part's dimensions or features, or a drawing's data, are setup to be driven by the user's input automatically in the background via references/macro/API.

• ###### Re: Parametric?........ What do you understand it to be?

Simply put, like my Texan friend Glenn Schroeder, if we change a dimension in the model (or drawing) it updates elsewhere.

Steve C

• ###### Re: Parametric?........ What do you understand it to be?

For me, Parametric is:

- When you model your assembly in a way that almost every mate is connected to a plane (not a surface).

- All your sketches and mating is as symmetric as possible.

- Add some "simple equations" that helps updating the assembly when changing some key dimensions.

- Using relations in the sketch can also be helpful to achieve a parametric design.

maybe there are some more points to add but this is what my understanding to "PARAMETRIC".

Regards,

• ###### Re: Parametric?........ What do you understand it to be?

I hate coming in on the tail end of these things, but its good there is so much feedback. Great question, by the way, Dave Bear!

To me, parametric is when you have a dimension or other parameter, like feature end condition, pattern type, etc. which can be changed to alter the model. I usually think of parametric as being within a single part (intra-part), but I guess we have to include associative (between parts) behavior and in-context (between parts in the context of an assembly) in there, because these can both be parametric as well.

One thing I often point out in discussions about parametrics is that history-based is not the same as parametric. CAD that is not history-based can absolutely be parametric. Sometimes when I suggest someone use direct edit, they say "I don't want to give up parametrics". Direct edit applies dimensions directly to the 3d solid, and you can change those directly. You can also apply relations between 3d faces in the way that you apply relations between sketch elements (parallel, perpendicular, concentric, etc).

So parametrics does not exclude all implementations of direct edit.

• ###### Re: Parametric?........ What do you understand it to be?

hmm,.. Parametric .. early on.. it meant Driven/Variable, either by equations or by dimensions.

.. for me, the are built in Parameters, mathematical rules which identify entities (curve, line, arc, circle, point,..)  and surface(boundaries) or bodies (brep)... and how they interact..  within CAD tools (Geometric modeling kernels; Parasolid, Acis, C3D, Granite,..) to parametrically drive or manipulate (push/pull, direct) geometry.

• ###### Re: Parametric?........ What do you understand it to be?

Like many have already stated, for me parametric means controlling the shape/size of sketch, features, models, assembly, etc. by changing the values that defines the shape/size.

• ###### Re: Parametric?........ What do you understand it to be?

Dave Bear wrote:

Hi all,

Please don't go and use google, Wikipedia and the likes for generic answers, I'm actually interested in what your honest and at the moment understanding of "Parametric" is.

Dave.

Good question Dave... Funny story about the word "parametric": One of the civil engineers here showed me a program they use to "parametrically" "model" bridge components.  Basically it is a dialog box where they enter data and hit a button and they get a 2D Cad file.  I asked, "What if you need to change one of those parameters later?" The answer was, you have to start over... The company that sold the Department the software is Bentley.  I got on there website back then and surely enough they were claiming it was parametric.

Fast forward a few years and I read somewhere that Bentley is now licensing the parasolid kernel and they are making a new product and have removed the word "parametric" from the description of the software I described above...Here's the funny part, they used to own the parasolid kernel and sold it in 1998 along with their real parametric program (which has now become SolidEdge).

To answer your question, parametric to me means driving or driven.  A dimension can drive another or several, up to and including the whole part and assembly... Oh, and you can make a change at any time...Stupid Bentley... Have I let my feelings for Bentley show?

• ###### Re: Parametric?........ What do you understand it to be?

Such a multitude of great answers.

All definitions should be worded in such ways, thanks guys, much appreciated.

Dave.

• ###### Re: Parametric?........ What do you understand it to be?

Controlled by constaints,rules or logarythms.

that's my understanding

• ###### Re: Parametric?........ What do you understand it to be?

logarhythms? you mean algorithms, right?

• ###### Re: Parametric?........ What do you understand it to be?

Maybe Largarhythms right next to the Smalarhythms

• ###### Re: Parametric?........ What do you understand it to be?

aye,

1 off them, n I bet I spelt it incorrectly as well??

• ###### Re: Parametric?........ What do you understand it to be?

Yeah, and you spelled "const(r)aints" wrong too, but who's counting? We're all engineering types here. I'm glad people don't point out all of my errors. I'd have to look up how to spell "logarithm", to be honest.

• ###### Re: Parametric?........ What do you understand it to be?

I am a lot more used to numbers

• ###### Re: Parametric?........ What do you understand it to be?

Going to basics...

Parametric = controlled by parameters

Parameters include (not limited to) variables, equations, constants, dimensions, constraints