Affine transforms - matrix algebra
martin.desruisseaux at geomatys.fr
Mon Jul 23 06:20:45 PDT 2012
Le 23/07/12 14:01, Pavel Safrata a écrit :
> On 23.7.2012 12:09, Martin Desruisseaux wrote:
> Unlike in J2D our Pts will have three coordinates, right? Or do we
> want transform2D and transform3D?
Yes, I was thinking about 3D-points. Maybe it is not necessary to
support 2D-points, since the existing Java2D classes can fit that need...
> I'm not sure about the floats. I don't mind adding those methods but
> is it OK for us to work with floats here and nowhere else? Shouldn't
> we then allow for floats at least for all the other arrays in Affine
I didn't though about the fact that 'float' are used nowhere else in
JavaFX... This is a good point.
Does JavaFX plans to support big geometries someday? For example
world-wide coast lines, in which case using 'float' instead of 'double'
make a huge difference on memory usage?
> To me this sounds a bit frightening. I may be wrong but I believe that
> the "ulps" are there to deal with representability of certain numbers
> in floating-point types but not with different math engines producing
> different results - I believe the results may be up to one ulp wrong
> but are reliably stable among all platforms. I'm a bit afraid that
> providing unstable results would violate at least some unwritten
> conventions. But I'm not an expert here, I might be wrong.
My (maybe naive) understanding was that StrictMath reliably produces
stable results among all platforms, while Math allow some
platform-dependent flexibility. In our implementation of a map
projection library making extensive use of Math.sin and the like, I do
have noticed slight platform-dependent variations.
Transform doesn't have to use the "ulps" wording; the actual question is
whatever Transform should allow hardward accelerations at the expense of
strict cross-platform stability. It may be worth to note that if my
understanding of java.lang.Math trigonometric functions is not wrong,
then this slight cross-platform variability already exists in Transforms
having a rotation calculated from an angle.
> We may use MAT for the getRow/getCol - it would specify from what
> matrix the col/row will be taken (each pair of values would provide
> similar behavior except for one of them allowing to read the last line).
This interpretation works for me. Anyone else?
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