Logarithms: Better than bad, they’re good!

Yesterday’s work was focused on two different TO-DO items:

1) I did a little bit of work on the position dialog box, as requested on the forum a few days back. The position dialog has two modes, incremental and not-incremental (I’ve been calling that one absolute), where the position indicated to the dialog is either applied against an object’s current position (incremental), or against the origin of the coordinate space (absolute). That mode is selected by a checkbox, the requested feature was to make the state of that checkbox persist between uses.

Screen Shot 2015-04-24 at 2.13.25 pm

In addition to making the checkbox state persistent, I ended up also changing around the transitions between the two modes a little bit, so now that part works a little more intuitively. Now, when incremental mode is entered, the GUI widgets are initialised to reflect the equivalent incremental placement to the change in absolute position that had been in the GUI before.

I suppose a video clip would’ve been a clearer way to convey the original problem and my changes…

2) The auto-scale in Drawing had a few problems, so I’ve re-worked two areas to resolve those.

First, there’s a little function (Attributed to David Eppstein, whose blog led me off to reading about the Harriss spiral – neat stuff) that takes a scale value and computes a ratio of two integers that closely approximates that scale. The problem was that the function wasn’t really setup for handing big or small scales, so I wrapped it up with a little math to essentially deal with adding 0s onto either the numerator or denominator depending on the scale.

Second, the algorithm for calculating the initial scale to use didn’t handle small scales very well. The re-work there was a little more involved, but fortunately a lot of my earlier work on the placement of orthographic views was useful.

So, now it’s easy to use the drawing workbench for bigger or smaller things than it used to be, though there are still a couple issues. One of them is that there’s a hard-coded level of detail parameter somewhere, which I intend to do something about. So, right now if I try to draw a sphere the size of Earth, then it gets computed to some absurdly high resolution, 0.01mm or something along those lines. There’s a similar problem in the regular 3D view part of FreeCAD too, for instance at the default settings a circle drawn in Sketcher looks like a 30-something sided polygon, so maybe that issue requires a bit more thought.

One thought on “Logarithms: Better than bad, they’re good!

  1. Luke Parry

    Ahh yes,

    In Sketcher, unless this has changed, the discretisation of curves for arcs / circles was hard coded to something like PI/16, which I never liked. With Drawing Projections, I am not sure if there will be control:

    It is related to the class HLRBRep__Algo, but there is no parameter to control the resolution as this is fixed because it uses an exact representation.

    Possibly I have intepreted this wrong and you are talking about the GUI Drawing code. Arcs are drawn using a custom function ( void QGraphicsItemViewPart::pathArc) to ensure a consistent and correct arc orientation is used. I never solved it using a simpler primitive.

    I guess the discretisation is related to line ~626 in QGraphicsItemViewPart.cpp

    n_segs = qCeil(qAbs(th_arc / (M_PI * 0.5 + 0.001)));

    You could try tweaking this and see if it improves things. Then making this a Parameter Setting for the Drawing Module if it does.

    Hope that helps,



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