# geometry¶

## Pose¶

Pose3 defines the 3D Pose as a 3D transform: [R|C] t = -RC

// Define two poses and combine them
Pose3 pose1(RotationAroundX(0.02), Vec3(0,0,-2));
Pose3 pose2(RotationAroundX(0.06), Vec3(-1,0,-2));
Pose3 combinedPose = pose1 * pose2;

// Apply the pose to a 3DPoint (World to local coordinates):
const Vec3 pt = combinedPose(Vec3(2.6453,3.32,6.3));


## Frustum & Frustum intersection¶

Define a camera Frustum from Pose3 and intrinsic parameters as:

• an infinite Frustum (4 Half Spaces) (a pyramid);
• a truncated Frustum (6 Half Spaces) (a truncated pyramid).

This structure is used for testing frustum intersection (see if two camera can share some visual content).

// Build two truncated frustum and test their intersection
Frustum frustum1(somedata, minDepth, maxDepth);
Frustum frustum2(somedata, minDepth, maxDepth);
bool bIntersect = frustum1.intersect(frustum2);

// Build two infinite frustum and test their intersection
Frustum frustum1(somedata);
Frustum frustum2(somedata);
bool bIntersect = frustum1.intersect(frustum2);


## 7DoF registration between point set¶

Find the rigid registration between point set using a scale, rotation and translation model.

// Simulate two point set, apply a known transformation and estimate it back:
const int nbPoints = 10;
const Mat x1 = Mat::Random(3,nbPoints);
Mat x2 = x1;

const double scale = 2.0;
const Mat3 rot = (Eigen::AngleAxis<double>(.2, Vec3::UnitX())
* Eigen::AngleAxis<double>(.3, Vec3::UnitY())
* Eigen::AngleAxis<double>(.6, Vec3::UnitZ())).toRotationMatrix();
const Vec3 t(0.5,-0.3,.38);

for (int i=0; i < nbPoints; ++i)
{
const Vec3 pt = x1.col(i);
x2.col(i) = (scale * rot * pt + t);
}

// Compute the Similarity transform
double Sc;
Mat3 Rc;
Vec3 tc;
FindRTS(x1, x2, &Sc, &tc, &Rc);
// Optional non linear refinement of the found parameters
Refine_RTS(x1,x2,&Sc,&tc,&Rc);

std::cout << "\n"
<< "Scale " << Sc << "\n"
<< "Rot \n" << Rc << "\n"
<< "t " << tc.transpose();

std::cout << "\nGT\n"
<< "Scale " << scale << "\n"
<< "Rot \n" << rot << "\n"
<< "t " << t.transpose();