Abstract of the Master's Thesis
Helsinki University of Technology
Department of Surveying

Henrik Broman

Three-dimensional positioning of a moving object

Chair Photogrammetry
Supervisor Prof. Henrik Haggrén
Instructor M.Sc. Esa Leikas
Date 20.3.1997
Number of pages 85
Keywords Videocompression, measuring objects in motion, Mapvision-system
Language Swedish

At the beginning the difference between photogrammetric on-line and off-line systems is briefly described and afterwards the functionality of real-time photogrammetric measuring system is explained. Mapvision-system is a photogrammetric measuring-system developed for industrial applications.

As part of the diploma-work an application was developed in Mapvision Ltd for the ship-laboratory in Otaniemi. The 3-dimensional positioning of a ship-model in motion is based on simultaneous framegrabbing with 2 CCD video-cameras. CCD cameras functioning with the European CCIR standard produce 25 images/second. This means that the data transfer rate must be essential. For this reason and because of the large storage requirements for digital images two computers has been used in this application, one for each camera. Videocompression technique based on the M-Jpeg standard has been used when compressing digital images.

A closer study of the image-coordinates accuracy when compressing images with the M-Jpeg standard was done. Further the variation of the compression ratios influence on the size of the compressed image was checked. The functionality of the compression algorithm we used was checked based on the number of skipped frames when increasing the compression ratio.

In chapter four the calibration method used for convergent photogrammetric measuring is described. Calibration of a Mapvision-station is based on bundle adjustment. This means that the mathematical model behind the calculations of the 3D-coordinates are directly related to the 2D-coordinates, in other words, no transformations or simplifications are needed. This is the reason for the high accuracy that has been achieved.

Chapter five is about videocompression. The redundancy in digital images can be reduced by videocompression but a too radical compression will cause decreased measuring results. The compression methods have been divided into two different categories, lossy and lossless. For measuring aims only lossless methods can be used. The lossy methods cause lost in image-quality and pixel-information as well as geometric and radiometric degradations. Further an inventory of video compression standards used today was done. A description of M-Jpeg, Mpeg and H.261 standards was done. Jpeg is a standard for compression of separate static images. M-Jpeg includes a video sequence with many compressed images one after another. Mpeg compresses images in video sequences also by using information from arounding images. The intended applications of H.261 standard are for videophone and videoconferencing.

In the last chapter was a summary of the diploma work done.


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