Sunday, 27 March 2011

Wrapping and interfacing compiled code into more flexible and user-friendly programs using Zenity and Bash

Subtitles include:

1. How to reconstruct the three-dimensional shape of an object in a scene in a very inexpensive way using shadow-casting
2. How to write and execute a matlab script from a bash script

I've written a bash script - - which is a wrapper for a set of programs for the reconstruction 3D surface of an object in a series of photographs using the ingenious shadow-casting algorithm of Jean-Yves Bouguet and Pietro Perona

The script relies heavily on the GUI-style interfacing tools of Zenity and acts as an interface and wrapper for the algorithm as implemented by these guys. It will also write and execute a matlab script for visualising the outputs.

This script should live in a directory with the following compiled programs, all available here:
1. ccalib (performs the camera calibration to retrieve the intrinsic parameters of camera and desk)
2. find_light (performs the light calibration to find light-source coordinates)
3. desk_scan (does the 3d reconstruction)
4. merge (merges 2 3d reconstructions, e.g. from different angles)

and the following matlab script:
1. selectdata.m (available here)

When the makefile is run, it creates the compiled programs in the ./bin directory. It's important to consult the README in the main folder as well as within the 'desk_scan' folder to have a clear idea of what the program does and what the input parameters mean.

My program will check if the camera calibration and light calibration files exist in the folder and if not will carry them out accordingly then several reconstructions are carried out, and the outputs merged. Finally matlab is called from the command line to run 'p_lightscan_data.m' to visualize the results.

when the script finishes there will be the following output files:
1. xdim.txt - max dimension to scan to
2. params - camera calibration parameters
3. data - camera calibration data
4. light.txt - light calibration parameters
5. sample.pts - [x,y,z] of object, in coordinates relative to light source
6. sample_lightscan1.tif - filled colour contour plot of reconstructed object
7. sample_lightscan2.tif - mesh plot of reconstructed object

I've tried to keep it flexible. It will run only the elements it needs to. For example, if the camera or lighting has been carried out before for a different object it will pick up on that. Also, the program can be invoked by passing it two arguments (path to folder where sample images are, and what sequence of contrasts to use for the reconstruction), which avoids having to input with the graphical menus. Example usage:
1. bash
2. bash /home/daniel/Desktop/shadow_scanning/sample/bottle

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