Re: Constraint finishing: "Ideal"

On 9/17/14 8:05 AM, Harald Alvestrand wrote:
> On 09/16/2014 11:00 PM, Harald Alvestrand wrote:
>> https://github.com/w3c/mediacapture-main/pull/20
> +                        For all numeric non-required constraints
> +                        (height, width, framerate, aspectRatio,
> +                        sampleRate and sampleSize), use the
> +                        formula <pre>(actual == 0) ? ideal : |actual -
> +                        ideal|/actuall</pre>.

Great! I've raised nits in git, but thought I'd raise discussion-worthy 
points here on the list:

 1. I thought the algorithm was to divide by ideal, not actual [1]

 2. Doesn't "All numeric ... constraints" include future numeric
    constraints? I suggest:

      * change text to: (currently: height, width, frameRate,
        aspectRatio, sampleRate and sampleSize)".
      * change algorithm to tolerate negative numbers: |(actual -
        ideal)/ideal|.

 3. By summing up distances of different numeric constraints, we're
    comparing apples to oranges, which is fine as I don't have a better
    idea. But, shouldn't we at least give equal weight to each numeric
    constraint? I think having distances converge toward 1 would produce
    fairer comparison between constraints [2], and suggest:

      *   change algorithm to have distance converge toward 1: |(actual
        - ideal)/max(|ideal|,|actual|)|


> + For all non-required string and enum
> +                        constraints (sourceId, groupId, facingMode,
> +                        echoCancellation), use the
> +                        formula <pre>(actual == ideal) ? 0 : 10</pre>.

I think 1 rather than 10 would be the "equal weight" number, and that 
anything larger trumps the algorithm, and users should just use exact 
instead. The edge-cases lost by this were too complicated anyway, and 
should be weighed against the edge-cases afforded by 1.

.: Jan-Ivar :.

[1] 
http://lists.w3.org/Archives/Public/public-media-capture/2014Aug/att-0005/Finding_an_-Ideal-_Algorithm__2_.pdf#Page=4
[2] 
http://lists.w3.org/Archives/Public/public-media-capture/2014Aug/0041.html