PTV Files

The PTV program generates several files for each frame.

1. File Extensions

Each file is encoded according to the Experiment and Frame number as follows: ****.XXXYYYYY, where **** is the file name (see further on), XXX is the experiment number and YYYYY is the frame number in the experiment. (e.g. cam1.18612740 is file cam1 for frame 12,740 in experiment 186.)

2. File names

a.In the Image folder

The image folder contains data from all (4) cameras in the experiment, each frame has 8 files (frame is the extension as described above):

  1. Image Files

    cam1.*frame*, cam2.*frame*, cam3.*frame* and cam4.*frame* - are files representing the images encoded in tiff format. Thus e.g. cam1.18612740 is the tiff image shot from camera 1 at frame 12740 of experiment 186.

  2. Targets Files

    Each image file has a target file associated with it, and named the same as the image with _targets added (e.g. cam1_targets.18612740). These files contain information on all the detected particles in the image, and is formatted as a tab-delineated text file, with the following structure:

    • The first row contains only one column, specifying the number of particles detected in the image.

    The other rows contain 8 columns each:

    • Particle number, x_location, y_location, area (pixels), x_length(pixels), y_length(pixels), sum of grayscale values in the particle, and correspondence.

    The particle ID is arbitrary, and is given by the detection algorithm.

    The x and y location are the location of the particle center of mass, and can thus have sub-pixel value.

    The area is the actual number of pixels taken up by the particle.

    The x and y length are the lengths of the major and minor axes of the particle (i.e. the length and the height of the particle if it were rotated to a horizontal position)

    The sum of grayscale is the sum of all greyscale values of the particle

    Correspondence is a flag that gets 1 if this particle was detected in more than one camera (i.e. if the particle is located on the intersection of 2 or more epipolar lines). A particle that with a positive number in the correspondence flag gets an ID in the rt_is file (see below), and is located at the corresponding line there.

  1. In the Res folder

    The res folder contains the tracking results from the whole sequence, and has 3 files per frame.

    1. rt_is Files

      These files contain the summary of the particles found in the frame, formatted as a tab-delineated text file, with the following structure: + The first row contains only one column, specifying the number of particles in the file.

      The other rows contain 8 columns each:

      • Particle number, x_location, y_location, z_location, id1, id2, id3, id4

      The particle ID is arbitrary, and is given by the tracking algorithm.

      The x, y and z location are the location of the particle in 3d, measured in mm.

      id1, id2, id3, and id4 are the particle IDs of that particle in corresponding camera frames. If the particle was not detected in a certain frame, its corresponding ID is -1.

      Note: rt_is files start with 1 and not 0, so the IDs need to be incremented by 1!

    2. ptv_is Files

      These are files used to track particles, and is essentially similar to the rt_is file, but with the following columns: + previous_particle, next_particle, x_location, y_location, z_location + Previous Particle is the particle ID of that particle in the previous frame, or -1 if it was first detected in the current frame. + Next Particle is the particle ID of that particle in the next frame, or -2 if it was not detected in the next frame.

    3. added Files

      These are files used to track particles added to the list of particles during the forward-backward-forward projection. It is essentially the same as the corresponding ptv_is file (see above), with the addition of a last column which is (always?) 4, and could signify the number of cameras over which the particle was identified.

For more information regarding to the PTV file system, look at the PTV file system descrption manual in the additional documentation section