example.h

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// Ceres Solver - A fast non-linear least squares minimizer
// Copyright 2010, 2011, 2012 Google Inc. All rights reserved.
// http://code.google.com/p/ceres-solver/
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// Author: keir@google.com (Keir Mierle)
//         sameeragarwal@google.com (Sameer Agarwal)
//
// Some Ceres Snippets copied for testing

#pragma once

#include <gtsam/3rdparty/ceres/rotation.h>

// Templated pinhole camera model for used with Ceres. The camera is
// parameterized using 9 parameters: 3 for rotation, 3 for translation, 1 for
// focal length and 2 for radial distortion. The principal point is not modeled
// (i.e. it is assumed be located at the image center).
struct SnavelyProjection {

  template<typename T>
  bool operator()(const T* const camera, const T* const point,
      T* predicted) const {
    // camera[0,1,2] are the angle-axis rotation.
    T p[3];
    ceres::AngleAxisRotatePoint(camera, point, p);

    // camera[3,4,5] are the translation.
    p[0] += camera[3];
    p[1] += camera[4];
    p[2] += camera[5];

    // Compute the center of distortion. The sign change comes from
    // the camera model that Noah Snavely's Bundler assumes, whereby
    // the camera coordinate system has a negative z axis.
    T xp = -p[0] / p[2];
    T yp = -p[1] / p[2];

    // Apply second and fourth order radial distortion.
    const T& l1 = camera[7];
    const T& l2 = camera[8];
    T r2 = xp * xp + yp * yp;
    T distortion = T(1.0) + r2 * (l1 + l2 * r2);

    // Compute final projected point position.
    const T& focal = camera[6];
    predicted[0] = focal * distortion * xp;
    predicted[1] = focal * distortion * yp;

    return true;
  }

};