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I'd like a comparison of how various CAD programs handle the task of creating relationships among objects that have been created independently and where the uses wants to change some parameters of one object and have the program adjust the parameters of the others automatically.
I'm interested in the variety of program interfaces - how the process "looks to the program user", not the underlying mathematics of the code that implements it.
For example, suppose I've created 4 rectangular solids that represent legs of a table. How would various CAD programs handle the task of establishing typical relations among the legs. For example, I might want the distance between the left front leg and the left rear leg to be the same as the distance between the right front leg and the right rear leg. I might want all the legs to have the same dimensions etc.
Establishing relations among independently created objects and then updating them when the user edits some parameter seems to be a complicated mathematical problem. Users might attempt to establish a set of relations that is self-contradictory. But I'd think that the task is so important that CAD programs would have discovered an efficient way of doing it.
My one data point is from the FreeCAD forum. The suggestion was to use "expressions". i haven't tried it yet, but I think it involves creating something like a spreadsheet whose cells have data for the objects. In a typical spreadsheet program, one "cell" in the sheet can be defined as a function of other cells.
Is that way things are done in other CAD programs?
(In my example, one could create a rectangular sold and then create the 4 posts in a dependent fashion by subtracting volumes from it, but I'm not sure this would allow the dimensions of the posts to be adjusted indepndently of the spacing between them - and my question still stands because surely other situations will arise when objects have been created independently before the designer considers how to assemble something from them.)
I'm interested in the variety of program interfaces - how the process "looks to the program user", not the underlying mathematics of the code that implements it.
For example, suppose I've created 4 rectangular solids that represent legs of a table. How would various CAD programs handle the task of establishing typical relations among the legs. For example, I might want the distance between the left front leg and the left rear leg to be the same as the distance between the right front leg and the right rear leg. I might want all the legs to have the same dimensions etc.
Establishing relations among independently created objects and then updating them when the user edits some parameter seems to be a complicated mathematical problem. Users might attempt to establish a set of relations that is self-contradictory. But I'd think that the task is so important that CAD programs would have discovered an efficient way of doing it.
My one data point is from the FreeCAD forum. The suggestion was to use "expressions". i haven't tried it yet, but I think it involves creating something like a spreadsheet whose cells have data for the objects. In a typical spreadsheet program, one "cell" in the sheet can be defined as a function of other cells.
Is that way things are done in other CAD programs?
(In my example, one could create a rectangular sold and then create the 4 posts in a dependent fashion by subtracting volumes from it, but I'm not sure this would allow the dimensions of the posts to be adjusted indepndently of the spacing between them - and my question still stands because surely other situations will arise when objects have been created independently before the designer considers how to assemble something from them.)
