Friday, 12 April 2013

Parametric dimensions in the Drawing Module


After about three weeks, of having to work on various assignments (nearing completion) and revision, I finally had a day off to work on dimension support in the Drawing Module (see above and compare to previous post).

Obviously the dimensions look much better and are correctly positioned and it also shares similar behaviour to sketcher where if the datum label lies outside the arrow lines change position accordingly.

Additionally the dimension can be set to the edge length in X or Y direction now quite easily by changing the dimension mode. Currently the dimensions only work for Straight Line edges, but I plan to address some support for vertexes and obviously circular arcs.

One of the interesting things that had to be thought was how to reference edges that are broken up into smaller segments by any geometry in front.


My first attempt at this failed miserably, where I thought I would reference each segment of the edge and find the ends from there but clearly it wouldn't work. After scratching my head, I thought the best way to go was getting the reference to the original geometry and projecting the whole edge and using this instead for dimensions.

The limitation with this strategy is that if the original reference isn't available you won't be able to get true parametric dimensions. Generally this isn't a problem - nearly all the time I have found references are available and if they aren't usually it is for curves projected onto a 3D view.

It was a bit of work to get to work, because I was using HLRBrep_Curve and that require figuring out what type of curve was produced when finished. I kept to this OpenCascade Algorithm to allow perspective projections if they were ever needed. Luckily it worked!

Behold Parametric Dimensions!

The big test really was to change the projection direction and see what happens...


And yes it worked - although the datum label positions need correcting, nothing else had to be changed. Now changing the geometry (nothing too drastic)...



It's a pleasing result because it's been several months in the works to get this working, not knowing if this would be even possible. Obviously there's a lot left to do.One of my biggest problems at the minute is that if there are changes in the Document Structure, the drawing view must be closed and re-opened

The next priority is to tidy the module up more as it's still feels experimental.