Update quaternions to prevent sign flipping

AustinSanders commented 2 weeks ago

Licensing

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Closes #603

We've had a few discussions on the dev team about how to accomplish this, and, for the most part, we decided on implementing these changes through subclassing. This PR does not do that, but instead makes a quick and easy change that accomplishes the same thing but without isolating the change to LineScan cameras.

In order to access the quaternions from a LineScanner, it is necessary to go the route of LineScanner.FrameChain.Rotation.quats, and there are two types of rotations -- TimeDependent and Constant, so we would need at least 3 subclasses to achieve this (a custom frame chain + two types of custom rotations). TimeDependentRotation and ConstantRotation classes have methods that instantiate other TimeDependentRotation or ConstantRotation, so a lot of the methods can't use simple inheritance -- they'd need to have their logic copied and objects changed.

Ultimately, subclassing is turning out to be pretty bloated and messy. It's still possible, but this seems significantly cleaner, and I don't think the functionality inherently needs to be isolated to LineScanners.

acpaquette commented 2 weeks ago

@AustinSanders Looks like a dawn test is failing from the change

AustinSanders commented 1 week ago

Running isd_generate on the image linked in the issue now results in quaternions that are represented correctly.

New representation:

[
        -0.00014084959512966424,
        0.06988009226932775,
        -0.9799806108855965,
        -0.18642627270348733
      ],
      [
        -5.113202307559794e-05,
        0.0698602605370718,
        -0.9799805775003425,
        -0.18643392691595587
      ],
      [
        3.8327611438555095e-05,
        0.06983938596985084,
        -0.9799806386052183,
        -0.1864414295623614
      ],
      [
        0.0001291419108749148,
        0.06981977990312137,
        -0.979980865507725,
        -0.1864475392580358
      ],

Old representation:

[
        0.00014084959512966424, <<< positive, decreasing
        -0.06988009226932775,
        0.9799806108855965,
        0.18642627270348733
      ],
      [
        5.113202307559794e-05, <<< positive, decreasing, about to flip sign
        -0.0698602605370718,
        0.9799805775003425,
        0.18643392691595587
      ],
      [
        3.8327611438555095e-05, <<< Should be negative, but flips all signs to keep scalar positive 
        0.06983938596985084,    
        -0.9799806386052183,    
        -0.1864414295623614
      ],
      [
        0.0001291419108749148, 
        0.06981977990312137,
        -0.979980865507725,
        -0.1864475392580358
      ],

Note that the positive scalar criterion is no longer enforced, and the sign performs a "natural flip" when crossing the 0 boundary, but the other quaternions do not flip.

DOI-USGS / ale

Update quaternions to prevent sign flipping #623

Licensing