CoCreate User Forum  

Go Back   CoCreate User Forum > Applications > CoCreate Modeling

Reply
 
Thread Tools Search this Thread Rate Thread Display Modes
  #1  
Old 03-23-2007, 10:24 AM
dszostak's Avatar
dszostak dszostak is offline
Registered User
 
Join Date: Oct 2002
Location: Boston, MA
Posts: 292
Post Cadalyst - MCAD Modeling—History . . . or Not?

MCAD Modeling—History . . . or Not?
History and nonhistory-based modeling software each has its own advantages.

"If you've kept track of the 3D-modeling business for very long, you've heard of a great battle that is raging: history-based modeling versus nonhistory-based modeling. Both camps have strong supporters. In fact, sometimes it sounds like partisan politics. Just because a system is parametric, is it better than one that isn't? I don't think so. I have used many systems over the years, and I can tell you from first-hand experience that both approaches have merits. But what's at the heart of the debate?"

March 2007
Written by Mike Hudspeth

http://manufacturing.cadalyst.com/manufacturing/article/articleDetail.jsp?id=410493

Click here to read more published articles about CoCreate.
__________________
David@CoCreate

Last edited by dszostak; 05-04-2007 at 03:28 PM. Reason: Added URL
Reply With Quote
  #2  
Old 04-01-2007, 08:10 AM
Steve Steve is offline
Registered User
 
Join Date: Mar 2003
Location: Alabama
Posts: 309
Re: Cadalyst - MCAD Modeling—History . . . or Not?

You know, just last week the fellow in the cube next to me, who is an Electrical Engineer who knows nothing about CAD but has heard me rant over the last 4 years about the problems with non-history based systems, came up with a great analogy that exactly describes the problem with non-history-based CAD packages.

He said:

"From your description of the problem, it sounds like someone took an Excel spreadsheet, with many cells driven by the contents of other cells, did a 'select-all', 'copy', and then did a 'paste special' with the 'values' option checked, and thus gutted all the relationships in the spreadsheet so that you had to manually do all the calculations by hand from then on."

From a non-mechanical guy, I was astounded at his grasp of the situation. This is precisely the situation that a non-history based CAD package puts the designer in. In order to "save" the user from having to deal with imbedded logic errors, non-history based systems simply gut the logic altogether, leaving the designer, and every future designer who has to work with the model, to know, understand, and manually maintain all geometric relationships themselves. It's like taking the tires off of my car and then telling me how great it is since I will never have flat tires anymore.

Really, that's what this whole debate about the two approaches is all about. Do you want to be able to define relationships between geometric features or not? Do you want to be able to control things about the model that don't physically exist, like theoretical intersections, or basic diameters of tapered holes or bosses or not? Non-history based modelers today severely limit your ability to do these kinds of things. Yes, with history-based systems you sometimes have to think hard from time to time to debug these relationships. With non-history-based systems you have to think hard all the time to maintain those relationships yourself. Eventually, most CAD users wake up one day and think, "Gee, wouldn't it be great if I could get the computer to keep track of these design relationships?" That is how these systems came to exist over a decade ago.

I guess there must be a market for this kind of CAD - CAD for people who can't understand the concept of imbedded geometric relationships, I guess. Just last week I heard of a new player in the non-history-based CAD market, "Spaceclaim" ( www.spaceclaim.com ) and watched their webcast demo. It, too, is a Boolean-style modeler, and it, too, seems to suffer from all the limitations that arise by not being able to define relationships in your designs. But they claim that out of some 5 million folks who could be taking advantage of 3D data, only 1 million or so actually make use of feature-based, parametric CAD tools, supposedly because they are too complicated for most users to understand. So they see those other 4 million folks as a good market to cater too.

Fortunately just this week I am starting a position at a new company that uses Solid Edge. I've never used it before, but after just 2 days I am already breathing intense sighs of relief at being able to, once again, actually nail things down in my model and let the computer take over the drudgery of keeping those relationships straight! Here's to being back in the top one-fifth again!

Steve
Reply With Quote
  #3  
Old 04-04-2007, 07:44 PM
Lim Chee Beng's Avatar
Lim Chee Beng Lim Chee Beng is offline
Registered User
 
Join Date: Nov 2002
Location: Malaysia
Posts: 210
Re: Cadalyst - MCAD Modeling—History . . . or Not?

Quote:
Originally Posted by Steve View Post
"From your description of the problem, it sounds like someone took an Excel spreadsheet, with many cells driven by the contents of other cells, did a 'select-all', 'copy', and then did a 'paste special' with the 'values' option checked, and thus gutted all the relationships in the spreadsheet so that you had to manually do all the calculations by hand from then on
Since the command created and remains there so long, doesn't it mean "paste special" commnad with "value" option useful?
Reply With Quote
  #4  
Old 04-05-2007, 01:27 PM
Steve Steve is offline
Registered User
 
Join Date: Mar 2003
Location: Alabama
Posts: 309
Re: Cadalyst - MCAD Modeling—History . . . or Not?

Quote:
Since the command created and remains there so long, doesn't it mean "paste special" commnad with "value" option useful?
That was not the point of the analogy. I was not trying to say it wasn't useful, even if in special cases. The question is, is it useful if that is your only option.

Clearly, the whole point and power of a computerized spreadsheet is to be able to create logical, mathematical relationships between cells. Sure, sometimes we like to use it like dumb graph paper, but if that was all we could do with it it would certainly become a very limited tool and far less powerful than it is with the ability to create such relationships.

In Excel, you have the choice to alter the logic, or gut it altogether. With non-history based CAD systems, you have no choice.

Steve
Reply With Quote
  #5  
Old 04-07-2007, 03:23 AM
tim heeney tim heeney is offline
Registered User
 
Join Date: Feb 2003
Location: London,UK
Posts: 17
Re: Cadalyst - MCAD Modeling—History . . . or Not?

Steve.
Your contribution has been well appreciated by myself over the past few years.
I have enjoyed your well expressed alternative opinions and i hope, i would not be alone in thanking you for being a very active member in this forum.
Good luck with the new job.
Tim.
Reply With Quote
  #6  
Old 04-07-2007, 01:51 PM
stefano_ME30's Avatar
stefano_ME30 stefano_ME30 is offline
Registered User
 
Join Date: Oct 2002
Location: Italy
Posts: 169
Re: Cadalyst - MCAD Modeling—History . . . or Not?

Quote:
Originally Posted by Steve View Post
Do you want to be able to define relationships between geometric features or not?
Steve

Hello Steve
often I've been confused if you are talking on "relationship" or "history" issue.
Baut relationship between features, it seems not war, because parametric is on the route of CoCreate "not history" based CAD.
It has to be improved, no dubt, to make it stronger and useful.
About "history", maybe it can add some in several cases, but I think, contestual with strong 3D parametric (not "parametric profiles" based) has is chances.
Parameters needs, history may be, but, I think it os not so hard without.
Execel is not "history based", but "relationship" based.
Think working with excel trying to change a value watching "history" of a cell, I thing it would not help so much.
I ever use excel working with OSD, ever, and what I miss is a direct OSD/Excel dialog (I have to pass throug txt file, really boring).
I see CatiA users that "dream" to use Excel, but when they try "actually" it seems ever a nightmare, believe me.

Be happy switching on SE, it is a great history-parametric SW that I like much more of SWX and has a great sheet-metal module.
Jump here when u like it.
ciao

Stefano
__________________
AGC
Memory: 12K fixed (ROM), 1K eraseable (RAM)
Clock: 1.024 MHz
Computing: 11 instructions, 16 bit word
Reply With Quote
  #7  
Old 04-09-2007, 12:30 PM
Steve Steve is offline
Registered User
 
Join Date: Mar 2003
Location: Alabama
Posts: 309
Re: Cadalyst - MCAD Modeling—History . . . or Not?

Quote:
Execel is not "history based", but "relationship" based.
The thing is, in the CAD world, "history" is the means by which you define features to which you then assign relationships.

Without history, you cannot define relationships to theoretical geometric constructs.

The classic, trivial example: Applying taper to a cylinder.

Let us say we have a cylinder, and then we apply taper to it, but then we wish to change the diameter of the underlying cylinder. A non-history based system cannot do this, because it doesn't "remember" that there was ever a cylinder present. But a history based system does, so it is trivial to modify the basic diameter of the now-tapered cylinder.

In a more sophisticated example, history is what allows you to define features which only exist at certain levels in an assembly. This is what allows you to create machined components based off of a casting.

History and Parametrics are closely intertwined and equally important to be able to adequately capture and imbed design logic in a model. Parametrics are the dimensions, history is what allows you to dimension to underlying theoretical geometry. Without history, you cannot apply parameters to what you need to control.

Steve
Reply With Quote
  #8  
Old 04-09-2007, 03:03 PM
phamil1 phamil1 is offline
Registered User
 
Join Date: Aug 2005
Location: Fort Collins, CO
Posts: 46
Re: Cadalyst - MCAD Modeling—History . . . or Not?

#1 fact when discussing this topic: History and non-history is completely independent from geometrical relationships/parametrics (including features-a simple collection of faces). It does however track the relationship from one modeling operation to another. It has to, to be able to rebuild the model on a regeneration. Geometrical relationships can be assigned to geometry, regardless of history or no history, including features.

The big question is how and when do you add this intelligence into the model. For history-based users, you add it into the modeling steps so that the model will regenerate properly when modified. Some modelers won't allow you to finish a modeling operation until you add the relationships. Others will let you go back into the history and add them later. However, it has to be embedded into the history. These relationships are solved serially based on the modeling steps (history).

For the non-history based users, relationships - including features (collections of faces) can be defined anytime, regardless of how, when or where the geometry comes from. These relationships are solved simultaneously using a parametric solver rather than just playing through the recorded steps. One of the big issues with this methodology is getting users to take the time to add this intelligence into the model - as it is not mandatory to the development, and/or modification, of the model. Non-history CAD companies still don't make it too easy to add this intelligence, although it is all there. It would be nice, if while in the modeling process, if it would be easier to add persistent relationships on the fly. It is getting better, but there is still work to do.

Another question: what is a feature? A recorded modeling step - or - a collection of faces that is important to the design or perhaps manufacturing. Actually, a feature that is important to the designer, may be completely useless to the NC programmer. It is not too uncommon for a feature definition to change through the product development process. A shell with 2 bosses with threaded holes in them might be important to the CAD user for a while, but the CAM user sees it as a pocket with two islands, and then two holes. Bottom line, it is important for relationships to adjust while geometry stays consistent, or perhaps geometry adjust while relationships stay consistent - something that a history-based system has huge problems with. The practice of rebuilding models in the history-based world is very common - this is one of the reasons.

I think we can all agree that this intelligence is important. But is history the best way to apply relationship? - Only as long as history makes it easier to add the relationships, (and this will not always be the case). The problem is that since the intelligence is maintained in the history of the model - it is ONLY useful to someone that has that exact same CAD system and really knows how to use it. I’ve seen many users struggle for hours to figure out how someone else modeled the part just so they could make a little change. Also, history structures are proprietary - there is no industry standard for the exchange of this information. Data exchange and interoperability is probably the #1 issue in the CAD business today - and maybe 90% of this comes from history trees. Is history really worth the overhead? In some cases, today it is very much worth it - in others, it is a complete waste. Both have their place.

Too bad we don't capture this intelligence as meta data in a database rather than proprietary data imbedded in the geometry. THEN we would have something.

Oh - sorry this got so long
__________________
Paul Hamilton
Technical Sales Manager (PTC)
http://p-hamilton.blogspot.com
Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -8. The time now is 04:54 AM.



Hosted by SureServer    Forums   Modeling FAQ   Macro Site   Vendor/Contractors   Software Resellers   CoCreate   Gallery   Home   Board Members   Regional User Groups  By-Laws  

Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.