Disclaimer: The code merely concentrates on how to obtain a rectlinear image (undistorted for our human eye) manually without fancy 3D rendering and texture mapping. It is not optimized to be efficient, just a small experiment project to understand the theory better.
The maths behind the reprojection is pretty staight forward [1]: The panorama is reprojected on the final image plane by determining the normalized 3D ray for each pixel in the rectlinear output image and converting it to spherical coordinates.
With these spherical coordinates we obtain the latitude and longitude of the point on the sphere and compute the corresponding position on the equirectangular panorama to determine the source pixel intensity value.
After acquiring the correspondence between output image pixel and equirectangular source pixel,
bilinear interpolation is used to reproject the image.
The c++ code uses OpenCV (>= 3.0) to read/ output the images.
The input image should be a 2:1 360x180 degrees field of view image to work properly.
[1]: Szeliski book "Computer Vision: Algorithms and Applications" p439
- OpenCV >= 3.0 (should be compiled with GUI support, using e.g. libgtk2.0, otherwise
cv::imshowwill fail) - libyaml-cpp-dev (
sudo apt install libyaml-cpp-dev)
From the project root, run:
mkdir build
cd build
cmake ..
make
cd .. && ./build/equi2rect_example
The output image is written to the specified path in the config.yaml file. A window will additionally pop up, showing the output image (might take some seconds).
You can play around with the values in the config file to get different output images.
Example images:
Rectified image with 20 degrees pan angle and 10 degrees tilt angle.
camera:
focal_length: 672
files:
img_dst_path: images/pano_rect.jpg # relativ path from directory where binary is executed
img_src_path: images/pano.jpg
viewport:
height: 1080 # px
# angles are in radians
pan_angle: 0.349066
roll_angle: 0.0
tilt_angle: 0.174533
width: 960 # px