Why Is Parametric Concept Important?

[Anonymous]

What Does Parametric Mean, And How Does The Parametric Change Engine Keep Everything Updated When I Make Changes? Why Is The Concept Important?

[aRcHiTeCt.JM · Accepted solution]

… hi @Anonymous 

… the term parametric in this context refers to the relationships among and between all elements of the model that enable the coordination and change management that REVIT provides. These relationships are created either automatically by the software or deliberately by the user as they work.

… a fundamental characteristic of a BIM - building information modeling application is the ability to coordinate changes and maintain consistency. The user does not have to intervene to update drawings, links, tags, and so forth.

… this concept is important because it is this capability that delivers the fundamental coordination and productivity benefits of REVIT

… change anything at any time anywhere in the project and REVIT coordinates that change through the entire project

… this change management is also one of the fundamental characteristics of a BIM solution.

[ToanDN]

This topic is so broad that I am extremely impressed that you actually got an elaborated answer with nice picture along with it in a mere 3 minutes after posting the question.

[SteveKStafford · Accepted solution]

As it relates to Revit specifically, Leonid Raiz (one of the founders) wrote this article "What Does Full Bi-Directional Associativity Mean?" at AUGI's forums in 2004.

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Leonid wrote:

There is some amount of confusion regarding full bi-directional associativity and it may be useful to spell out what it means. I don't really want to focus on the "my software is better than yours" aspect but would rather describe the meaning of terms "live" and "bi-directional associativity". Any product making claims to support bi-directional associativity has to be able to support examples of parametric and associative changes listed below.

Many existing products have some ability to update elements of a design when other elements change. However with an exception of Revit in many cases such updates are not automatic. Every case when a user has to take an explicit action to do an update creates a possibility of error and uncoordinated design documents. It also necessitates additional work by an end user. We also should not confuse the ability to display or edit a single underlying data model in multiple views with full parametric associativity between various elements of design.

There are 3 main classes of elements in any building design
(A) Building components (walls, roofs, doors, windows, floors, etc.)
(B) Views including schedules and sheets
(C) Annotations (text notes, dimensions, spot elevations, etc.)

I do not want to diminish benefits of other products, they are quite good at what they do.
On the other hand Revit is the only product on the market today which was engineered from the ground up to provide full bi-directional associativity between all 3 main classes of elements.

Below are the examples of this associativity and corresponding parametric change propagation from elements of class to another.

Building components to building components
a. Move one wall and connected adjacent walls adjust to become longer or shorter
b. Move walls and a floor adjusts to cover area enclosed by walls
c. Raise/lower a roof and attached walls grow or shrink
d. Thicken a wall and door frames adjust to new thickness
e. Raise a level and all elements placed of this level will follow.

Building components to views
a. Change to a building component is automatically reflected in all graphical views without additional user actions
b. Move walls and room schedule updates room areas
c. Add or remove building components or change parameters of existing elements and schedules update automatically

Building components to annotations
a. Change geometry and dimension value updates
b. Move things higher or lower and spot elevation reflects new heights
c. Move walls and room tags update displayed area values
c. Changes to properties of wall, windows, doors, etc. are automatically reflected in their tags

Views to building components
a. Any graphical view (plan, elevation, section, callout) may be used to effect a change to building component
b. Changes to building components may be made by editing their parameters in schedules
c. Changes to view phase or level of detail automatically reflected in display of all building components shown by this view

Views to other views
a. Move section or detail view backward or forward and callouts move with their parent section
b. View and drawing schedules (view/drawing lists) may be used to change properties of other views and drawing

Views to annotations
a. Change view scale and all dimensions, text notes, etc. adjust to maintain their sizes on printed output
b. Place a view on a drawing sheet and view tags update to reflect sheet number
c. Change view scale and scale tag in view title on sheet updates

Annotations to building components
a. Change dimension value and building component changes accordingly
b. Changes to property values shown by tags automatically propagate to building components
c. Change elevation value displayed by level tag and level moves up or down
d. Impose dimension equality constraint or lock dimension value and building components behave accordingly

Annotations to views
a. Flip direction of section view tag and view forward direction flips.

Annotations to annotations
a. Change sheet number in a titleblock and the change will propagate through drawing to views placed on this drawing and then to their view tags (section and callout heads).

All these examples are made possible in Revit not only because it has a patent pending Parametric Change Engine (PCE) in the middle of its software architecture but also because all Revit's elements are implemented with parametric change in mind. There are countless other examples made possible by the PCE and the unifying notion of associativity between all 3 kinds of design elements.

Unless a product is implemented from the ground up with a PCE type of architecture its implementation may exhibit some examples of associativity but its change propagation capabilities are bound to be limited.

HTH

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