5/4/2023 0 Comments Raster formatsHence the given point lies between chains 3 and 4. Of all chains that line segment S participates in, chain 4 is the leftmost one. We find that it lies to the left of chain 5 since it lies to the left of line segment S. According to the tree, we must next test to determine on which side of chain 5 the point lies. And of all chains that line segment K participates in, chain 3 is the rightmost one. Hence for the point shown in Figure 14, it lies to the right of chain 3 since it lies to the right of line segment K of chain 3. Since chain 5 is above chain 4 on the search tree line segment S only need be tested on chain 5. For example, line segment S is shared on chains 4 and 5. If the test for chain B is below the test for chain A in the tree of Figure 14 then any line segment on chain A which is also on chain B will only appear in the test for chain A. Preparata and Lee also point out that even though line segments can be shared between chains, in the binary search of chains, each line segment need be accessed only once. The notation x:y means to the right of chain x and to the left of chain y. illustrates a binary search tree which can be used to determine between which pairs of successive chains in figure 13 a given point lies. The algorithm described by Preparata and Lee is based on organizing the line segments of the region boundaries into monotone chains.įigure 14. The worst algorithm to use in solving this problem is the simplest one: search through all regions and determine the first region in which the given point lies. The point in region problem is given a point, determine which region it is in. Because a complete review of these algorithms would be quite lengthy, in the next few paragraphs we give the reader a feel for them by describing only one of them, an algorithm to solve the point in region problem published by Lee and Preparata (1977). Each finds some way to use the order in a data point set to increase the search efficiency.Ī bibliography of papers discussing and describing these fast geometric search algorithms for vector format data is given at the end of this chapter. This research has shown that the typical brute force searching algorithms for vector format data are not the most efficient. This point of view which admits the possibility of data sets executing quicker in vector format is possible because of the recent advances made in the field of computational geometry. Rather it should be the worry of the system itself. The thesis of this chapter is that the data format question and its associated algorithm should not be the worry of a user of a spatial information system. ![]() Which algorithm will execute quicker depends on the characteristics of the data set being operated on. However, it is not necessarily the case that the simpler algorithm for raster format data will execute faster than the corresponding algorithm for vector format data because raster data typically has a much higher data volume. ![]() Raster format data has an advantage over vector format data in that the algorithms to determine in what region a pixel lies, to determine the boundary of a given region or to do polygon overlay, are simpler algorithms than the corresponding algorithms for vector format data. Haralick, in Map Data Processing, 1980 IV RASTER FORMAT VS. A popular program is Adobe Photoshop.A SPATIAL DATA STRUCTURE FOR GEOGRAPHIC INFORMATION SYSTEMS Most users use a paint program or image editor to create and edit raster images. ![]() What program can create a raster image?Īny program capable of opening one of the image formats mentioned above can also create a raster image. Vector images are used for logos, graphics, and text because they can be resized in any direction without distortion. For example, increasing the size of a small raster image distorts the image because the image editor is resizing each pixel in the image.īecause of this disadvantage, many printing companies that print business cards, posters, or any other large printing require the image to be a vector image. One of the biggest disadvantages of a raster image is the inability to resize the image without getting jaggies or other types of distortion. Today, almost all of the images you see on the Internet and images taken by a digital camera are raster images. The number defines the location, size, or color of the pixels. A raster image is an image file format that's defined by a pixel with one or more numbers associated with it. Raster may refer to any of the following:ġ.
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