Force nonnegative scale for Sim(3) #997
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As discussed in #995, for certain inputs,
Similarity3.Align()returns an object with negative scale.According to my derivation here, based on Zinnser05prip, the correct scale should not need an absolute value cast.
However, this PR adds an absolute value cast on the scale, and we can likely blame numerical instabilities as a reasonable motivation (the negative values I saw were relatively close to zero).