7SpatialResolutionToolsLectureNotes

7SpatialResolutionToolsLectureNotes - 1 GIS 4037c Dr....

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1 GIS 4037c Dr. Charles Roberts Unit 7 Spatial Resolution Tools Spatial resolution tools are tools that you use every day, but take entirely for granted. ALL computer graphics programs use spatial resolution tools. VERY few users have any idea how they work. You will know the concepts behind them after today. It is unlikely that you will need to know them in any great detail this semester, but for more advanced work, they are important. They are not covered in any other class you are likely to take. Computer Screen Resolution We are often confronted with problems that have to with the size of the image display, the size of the image itself, or the running time of the software. For instance, the image size often does not match the size of the computer screen, so we have to reduce or enlarge the image to fit entirely on the screen. A typical satellite image is about 3000 by 2000 pixels. The best computer display monitor is 1024 by 1024 pixels. Most monitors are smaller than this. The number of rows and columns available is a function of the particular monitor. There are tradeoffs between having the largest number of rows and columns displayed and the largest possible combinations of colors. For this reason, you can often set the screen resolution in the operating system (windows) or in the particular software. The way the screen resolution is described works like this: 1024 x 768 x 256 The first two numbers are the dimensions of the video graphics display, in pixel rows and columns. The third number is the pixel depth, or number of grey tones that can be displayed at one time. If an image is too large, say, 512 x 512, we cannot display the entire image at one time. We might want to change to a higher resolution screen, if we have that option. If we are already at the highest resolution possible, we will have to consider other options. There are three techniques that we use to do this. Each is simple to understand, but you need to understand what they do, and when it is appropriate to use them. The three techniques are called IMAGE MAGNIFICATION AND REDUCTION, IMAGE SUBSETTING, AND IMAGE RESAMPLING. Magnification and Reduction The graphic display is limited in terms of the number of pixels that it can display. The best system we have displays 1600 by 1200 pixels. Most modern computer users have a screen resolution of 1024 x 768. TM imagery (30 meter resolution) is over 3000 by 3000. DOQQs are 1
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7SpatialResolutionToolsLectureNotes - 1 GIS 4037c Dr....

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