Quick experiment again with Sectional Views & General Updates

I am midway during exam season (two weeks) long and things seems to be going swimmingly which I'm happy to report.

Over the past two weeks I've just spent some time tidying up the code and trying to fix a pretty nasty crash in QGraphicsview, anytime you updated the view. I really hope this has gone, but if during testing you suddenly experience a crash when the view updates, please inform me. It seems to have disappeared but esentially was a problem with incorrect bounding boxes as the usual case is. Additionally I've just tidyied up the code and improved the performance by having QGraphicsView using a backend cache, so it doesn't have to constantly redraw features when it is unecessary.

Today, I decided to have a day off revision, as to be honest I am fed up with the mundane repetitiveness. Apart from what I mentioned earlier I wanted to take a quick diversion from the orthographic project stuff I've recently been looking at which I've also made a few improvements on.

I wanted to take a look back at sectional views which I had to give up on because I couldn't correctly produce faces by processing each edges in the correct order. I mentioned this in a previous blog entry some time ago.

Eventually I managed to find the problem and unexpectedly half of the result was from the drawing code itself, where although the edges were in the correct order there was a chance these could be reversed.  Eventually I got something working on most faces.

I then updated the work on the sectional view and behold...

This was taken from a simple planar cut through straight through the centre:

To be honest it's only a proof of concept that i've created over the past few hours. I have identified that some changes are needed to improve the structure to something less 'hacky'. The other limitation is there won't be use of 'true' dimensions because references are lost when the boolean cut is applied.

----------- UPDATE ---------

We all like updates. Spent this evening on it again, rather naughtily and tidied up the areas that I weren't happy with. The section plane is now it's own object in the drawing view, so I had to build up some infrastructure around there which I am more happy with. Now we can finally get some sectioning goodness!

I need to fix a bug that's causing a segfault, so hopefully soon I can push this for people to try and experiment with probably more complicated shapes. 

Drawing Module: Section Views

This past week has been a tremendously busy one at University, but in the few bits of time I do have available, I have been looking at incorporating section views into my experiments on the Drawing Module. For those unfamiliar what a 'Section' views, below is an example. These are highly important in mechanical design and allow complex features to be seen and also annotated

Sectional View Along Axis A-A

Yorik, already did some work within his arch module purely using the python capabilities within FreeCAD. This can be used in the latest release of 0.13. His solution is simple but works well. Below is a representation of the sectioning algorithm (I am currently waiting for a download to finish so found the time to draw it)

1. The user defines a 3D plane. The 3D Plane is then checked to see if it intersects with the object
2. The bounding box for the FreeCAD part is then projected onto the cutting plane - there are 8 points.
3. The maximum size of each projection on the principal axes of the plane are found. These are then turned into an extruded box prism and a boolean cut operation leaves the remaining part.
4. The remaining sectioned part remains. The faces are then projected and if they are coincident with the cutting plane it will be sectioned face.

Interestingly enough I decided to mimic such behavior in the Sectioned View of this. Although relatively simple, in c++ requires finding the correct modeling algorithms in OpenCascade. After some mind boggling, I eventually got something crude to work.

The functionality I am aiming towards is something similar to the functionality in other commercial CAD packages (namely Solidworks). My view is that using a 3D plane to section an object can be slightly tedious and awkward - atleast until we get a plane feature with the arrival on the Assembly Module. Instead I think it is more practical to create a section in the 2D Drawing User Interface.

 The user can create both 3D and Orthographic projections of the object and the user will 'draw' a section line AA in 2D. Upon completion this will create a new 'Section' View to the side that can be freely positioned.

The section plane is calculated simply by taking the cross product of the current view normal and the line, which produces the new normal of the plane.

This would hopefully cover most cases, but it should also allow an arbitrary plane to be set to create more flexibility when sectioning. 

The one complication that arises is that references will be lost because of the boolean operation. This will be of concern atleast until we get the more robust naming mechanism.

Hatching:

Any sectioned faces or even chosen ones should be fillable with a hatch pattern. This can be detected automatically if the face is coincident on the plane. I haven't yet decided the approach for storing hatching information but should be relatively straight forward.

I am hoping to get some more of this done tonight or tomorrow and have something to show but that all depends on University work...