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u35-RASTER STORAGE

# u35-RASTER STORAGE - UNIT 35 RASTER STORAGE...

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Sheet1 Page 1 UNIT 35 - RASTER STORAGE <toc.html#UNIT35> UNIT 35 - RASTER STORAGE Compiled with assistance from Donna Peuquet, Pennsylvania State University # A. INTRODUCTION <#SEC35.1> * Why use raster? <#SEC35.1.1> * Objectives <#SEC35.1.2> # B. STORAGE OPTIONS FOR RASTER DATA <#SEC35.2> * What if there is more than one layer? <#SEC35.2.1> * What do raster systems store in each pixel? <#SEC35.2.2> * Raster/Vector combinations <#SEC35.2.3> # C. RUN ENCODING <#SEC35.3> * Problems <#SEC35.3.1> # D. SCAN ORDER <#SEC35.4> * 1. Row order <#SEC35.4.1> * 2. Row prime order (Boustrophedon) <#SEC35.4.2> * 3. Morton order <#SEC35.4.3> * 4. Peano scan (also Pi-Order or Hilbert) <#SEC35.4.4> * Comparing scan orders <#SEC35.4.5> # E. DECODING SCAN ORDERS <#SEC35.5> * Method <#SEC35.5.1> * Generalization <#SEC35.5.2> # REFERENCES <#SEC35.6> # DISCUSSION AND EXAM QUESTIONS <#SEC35.7> # NOTES <#SEC35.8> The latter portion of this unit and the following two require familiarity with numbering systems in base 2 and 4 as well as techniques for conversion between these and decimal. You may wish to provide your students with some background material on these topics before tackling these units. UNIT 35 - RASTER STORAGE Compiled with assistance from Donna Peuquet, Pennsylvania State University A. INTRODUCTION <#OUT35.1>

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Sheet1 Page 2 Why use raster? <#OUT35.1.1> * data are acquired in that form from remote sensing, photogrammetry or scanning * is a common way of structuring digital elevation data * raster assumes no prior knowledge of the phenomenon, sampling is done uniformly o knowledge of variability would allow us to sample more heavily in areas of high variability (rugged terrain) and less heavily in smooth terrain * data are often converted to raster as a common format for data interchange * for merging with remote sensing images or DEMs * raster algorithms are often simpler and faster o e.g. buffer zone generation is simpler in raster * raster may be appropriate if the solution requires uniform resolution, e.g. in finding optimum routes for linear features such as power lines, or in inferring the locations of stream networks from DEMs Objectives <#OUT35.1.2> * there are many options for storing raster data (many data structures) * some are more economical than others in use of storage * some are more efficient in access and processing speed * this unit looks at some of the options and issues involved * many of these issues were introduced in Unit 4, they are expanded upon here B. STORAGE OPTIONS FOR RASTER DATA <#OUT35.2> * by convention, raster data is normally stored row by row from the top left o this is the European/North American reading order o is also the order of scan of a TV image * example * the image A A A A A B B B A A B B A A A B
Sheet1 Page 3 o would be stored in 16 memory positions, one for each pixel, in the sequence: A A A A A B B B A A B B A A A B What if there is more than one layer? <#OUT35.2.1> * two options: 1. store the layers separately o this is the normal practice 2. store all information for each pixel together o this requires extra space to be allocated initially within each pixel's storage location for layers which might be created later during analysis o this is usually difficult to anticipate

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u35-RASTER STORAGE - UNIT 35 RASTER STORAGE...

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