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// Ceres Solver - A fast non-linear least squares minimizer
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// http://ceres-solver.org/
//
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//
// Author: keir@google.com (Keir Mierle)
//
// A minimal, self-contained bundle adjuster using Ceres, that reads
// files from University of Washington' Bundle Adjustment in the Large dataset:
// http://grail.cs.washington.edu/projects/bal
//
// This does not use the best configuration for solving; see the more involved
// bundle_adjuster.cc file for details.
#include <cmath>
#include <cstdio>
#include <iostream>
#include "absl/log/initialize.h"
#include "absl/log/log.h"
#include "ceres/ceres.h"
#include "ceres/rotation.h"
// Read a Bundle Adjustment in the Large dataset.
class BALProblem {
public:
~BALProblem() {
delete[] point_index_;
delete[] camera_index_;
delete[] observations_;
delete[] parameters_;
}
int num_observations() const { return num_observations_; }
const double* observations() const { return observations_; }
double* mutable_cameras() { return parameters_; }
double* mutable_points() { return parameters_ + 9 * num_cameras_; }
double* mutable_camera_for_observation(int i) {
return mutable_cameras() + camera_index_[i] * 9;
}
double* mutable_point_for_observation(int i) {
return mutable_points() + point_index_[i] * 3;
}
bool LoadFile(const char* filename) {
FILE* fptr = fopen(filename, "r");
if (fptr == nullptr) {
return false;
};
FscanfOrDie(fptr, "%d", &num_cameras_);
FscanfOrDie(fptr, "%d", &num_points_);
FscanfOrDie(fptr, "%d", &num_observations_);
point_index_ = new int[num_observations_];
camera_index_ = new int[num_observations_];
observations_ = new double[2 * num_observations_];
num_parameters_ = 9 * num_cameras_ + 3 * num_points_;
parameters_ = new double[num_parameters_];
for (int i = 0; i < num_observations_; ++i) {
FscanfOrDie(fptr, "%d", camera_index_ + i);
FscanfOrDie(fptr, "%d", point_index_ + i);
for (int j = 0; j < 2; ++j) {
FscanfOrDie(fptr, "%lf", observations_ + 2 * i + j);
}
}
for (int i = 0; i < num_parameters_; ++i) {
FscanfOrDie(fptr, "%lf", parameters_ + i);
}
return true;
}
private:
template <typename T>
void FscanfOrDie(FILE* fptr, const char* format, T* value) {
int num_scanned = fscanf(fptr, format, value);
if (num_scanned != 1) {
LOG(FATAL) << "Invalid UW data file.";
}
}
int num_cameras_;
int num_points_;
int num_observations_;
int num_parameters_;
int* point_index_;
int* camera_index_;
double* observations_;
double* parameters_;
};
// 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 SnavelyReprojectionError {
SnavelyReprojectionError(double observed_x, double observed_y)
: observed_x(observed_x), observed_y(observed_y) {}
template <typename T>
bool operator()(const T* const camera,
const T* const point,
T* residuals) 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 = 1.0 + r2 * (l1 + l2 * r2);
// Compute final projected point position.
const T& focal = camera[6];
T predicted_x = focal * distortion * xp;
T predicted_y = focal * distortion * yp;
// The error is the difference between the predicted and observed position.
residuals[0] = predicted_x - observed_x;
residuals[1] = predicted_y - observed_y;
return true;
}
// Factory to hide the construction of the CostFunction object from
// the client code.
static ceres::CostFunction* Create(const double observed_x,
const double observed_y) {
return new ceres::AutoDiffCostFunction<SnavelyReprojectionError, 2, 9, 3>(
observed_x, observed_y);
}
double observed_x;
double observed_y;
};
int main(int argc, char** argv) {
absl::InitializeLog();
if (argc != 2) {
std::cerr << "usage: simple_bundle_adjuster <bal_problem>\n";
return 1;
}
BALProblem bal_problem;
if (!bal_problem.LoadFile(argv[1])) {
std::cerr << "ERROR: unable to open file " << argv[1] << "\n";
return 1;
}
const double* observations = bal_problem.observations();
// Create residuals for each observation in the bundle adjustment problem. The
// parameters for cameras and points are added automatically.
ceres::Problem problem;
for (int i = 0; i < bal_problem.num_observations(); ++i) {
// Each Residual block takes a point and a camera as input and outputs a 2
// dimensional residual. Internally, the cost function stores the observed
// image location and compares the reprojection against the observation.
ceres::CostFunction* cost_function = SnavelyReprojectionError::Create(
observations[2 * i + 0], observations[2 * i + 1]);
problem.AddResidualBlock(cost_function,
nullptr /* squared loss */,
bal_problem.mutable_camera_for_observation(i),
bal_problem.mutable_point_for_observation(i));
}
// Make Ceres automatically detect the bundle structure. Note that the
// standard solver, SPARSE_NORMAL_CHOLESKY, also works fine but it is slower
// for standard bundle adjustment problems.
ceres::Solver::Options options;
options.linear_solver_type = ceres::DENSE_SCHUR;
options.minimizer_progress_to_stdout = true;
ceres::Solver::Summary summary;
ceres::Solve(options, &problem, &summary);
std::cout << summary.FullReport() << "\n";
return 0;
}