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add comments about tangent space and covariance matrix ordering

release/4.3a0
John Lambert 2021-07-21 10:27:31 -06:00 committed by GitHub
parent 5fee983ff1
commit 28ecc3331b
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gtsam/sfm/ShonanAveraging.cpp
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@ -955,6 +955,8 @@ static BinaryMeasurement<Rot2> convertPose2ToBinaryMeasurementRot2(
"parseMeasurements<Rot2> can only convert Pose2 measurements " "parseMeasurements<Rot2> can only convert Pose2 measurements "
"with Gaussian noise models."); "with Gaussian noise models.");
const Matrix3 M = gaussian->covariance(); const Matrix3 M = gaussian->covariance();
// the (2,2) entry of Pose2's covariance corresponds to Rot2's covariance
// because the tangent space of Pose2 is ordered as (vx, vy, w)
auto model = noiseModel::Isotropic::Variance(1, M(2, 2)); auto model = noiseModel::Isotropic::Variance(1, M(2, 2));
return BinaryMeasurement<Rot2>(f->key1(), f->key2(), f->measured().rotation(), return BinaryMeasurement<Rot2>(f->key1(), f->key2(), f->measured().rotation(),
model); model);
@ -1001,6 +1003,8 @@ static BinaryMeasurement<Rot3> convert(
"parseMeasurements<Rot3> can only convert Pose3 measurements " "parseMeasurements<Rot3> can only convert Pose3 measurements "
"with Gaussian noise models."); "with Gaussian noise models.");
const Matrix6 M = gaussian->covariance(); const Matrix6 M = gaussian->covariance();
// the upper-left 3x3 sub-block of Pose3's covariance corresponds to Rot3's covariance
// because the tangent space of Pose3 is ordered as (w,T) where w and T are both Vector3's
auto model = noiseModel::Gaussian::Covariance(M.block<3, 3>(0, 0)); auto model = noiseModel::Gaussian::Covariance(M.block<3, 3>(0, 0));
return BinaryMeasurement<Rot3>(f->key1(), f->key2(), f->measured().rotation(), return BinaryMeasurement<Rot3>(f->key1(), f->key2(), f->measured().rotation(),
model); model);