Publication detail

Komprimace vektorových geodat

Authors: Čapek Jan

Year: 2004

Type of publication: článek v odborném periodiku

Name of source: E+M Ekonomie a Management

Publisher name: Technická univerzita v Liberci

Place: Liberec

Page from-to: 120-129

Titles:

Language	Name	Abstract	Keywords
cze	Komprimace vektorových geodat	Článek se zabývá problémem komprimace vektorových geodat, problémem, kterému není věnována v literatuře pozornost patrně z vžité představy, že vektorová goedata jsou sama o sobě tak úsporná, že nemá význam je dále komprimovat, na rozdíl od geodat rastrových, kde se naopak komprimace hojně používá.Jsou diskutovány dvě nejběžnější transformace používané v komprimačních programech a sice Fourierova transformace a vlnková (Wavelet) transformace. První z nich zejména pro názornost jak komprimace funguje spíše než pro skutečné použití. Skutečná výhoda komprimace vektorových geodat se může ukázat u komplikovaných polygonů, nebo linií tvořených velkým počtem vytvářejících bodů.	Geodata, geografický informační systém, komprimace, Fourierova transformace, Wavelet transformace.
eng	The vector geodata comprimation	In this contribution is discussed possibility of the vector?s geo-data compression. At the first is introduction to the needs of compression data, as example is used geographical information system which works with geo-data in vector and raster forms. The difference between both data types is explaining, as well. It is notice that usually the compression methods are used for the raster data and no for the vector data. For the experiment was used circle polygon created by means of the 16 segments, so for creation was used 17 points with x-coordinate and y-coordinate so together was needs 34 points for data transmissions. As the first compression methods the Fourier transform was used. The first step was direct Fourier transform from which we obtain spectrum for both points coordinate. From the figure one should see which points, better speaking which coordinate are near zero, so these points is possible omits for future calculation. This way is fundament of the compression. Now one obtain reduced set of points and these point enter to inverse Fourier transformation. The results are on the figure 6 and tables 2 and 3. The second compression methods was used the Wavelet transformation. Basically the way of compression was the same. After the direct transformation one should find the nearest zero points. After these manipulations the reduced sets of points enter to the inverse Wavelet transformation. The results are on the tables 4 and 5 and figure 9. Concussion: The compression of the vector?s geo-data is possible only for the complicated shapes created sufficient number of created points.	Geodata, geographic information system, comprimation, Fourier transformation, Wavelet transformation.

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