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Images, spatial data and matlab

Images, spatial data and matlab. Data types and storage:. Vector data - making polygons, outlines, like coastline. Data types and storage :. Raster data , 2D arrays, gridded data Color, or rainfall, or elevation. Raster data storage. 2d data

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Images, spatial data and matlab

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  1. Images, spatial data and matlab

  2. Data types and storage: • Vector data- making polygons, outlines, like coastline

  3. Data types and storage: • Raster data, 2D arrays, gridded data • Color, or rainfall, or elevation

  4. Raster data storage • 2d data • Computer stores data as bits (ones and zeros) • 1-bit array Ex: (1=white, 0=black) • More complex data: eight bits=byte • 1 byte=28=256 possibilities => gray scale with 256 intensities of black to white, or 256 values of a colorscale (use colormaps) • Still not good enough for good maps… • 24-bit system; 8 bits for each RGB channel=2563=16,777,216 colors • 24 bit storage requires lots of memory!!!

  5. Data formats: • Compuserve Graphics Interchange Format (GIF): • 256 colors, Compression without data loss-Designed for fast transfer over the internet, Good for line art, simple maps, cartoons, logos • Microsoft Windows Bitmap Format (BMP) • Native bitmap format for Windows OS,Converters exist to read and write BMP files on other platforms • Tagged Image File Format (TIFF) • Includes an image file header, a drectory, and the data in all available graphics and image file formats;Vector and raster versions;Designed to be very portable- any computer platform • BUT, evolution caused incompatibilites…Thousands of Incompatible File Formats • PICT • Apple;Rasters and vectors;PICT not supported by other platforms

  6. Data formats, con’t: • PostScript (PS) Encapsulated PostScript (EPS) • Xerox/ Aldus (Adobe)/Apple; Vector format • PS-generally single-page format, illustration of a text • EPS- included in other pages, contain combination of text, graphics, and images • Joint Photographic Experts Group (JPEG) • Image compression and format;Irreversible compression (data lost);Three channel- 24 bit true color • Portable Document Format (PDF) • Adobe;Cross-platform;Contains complete formatting of vector illustrations, raster images, and text; Highly compressed;Fast internet download

  7. Importing, Processing, Exporting Imageslab activity: • http://asterweb.jpl.nasa.gov/gallerymap.asp • Make new directory in your matlab space • Download and save image

  8. Importing, Processing, Exporting Images, con’t • On command line ….( pg 231) • Picture1=imread(‘name of image.jpg’); • imshow (Picture1); • PictureGray=rgb2gray (Picture1); • imshow (Picture1), figure, imshow(PictureGray); • Follow remaining instruction on pg 233-235 • NOTE there is a TYPO in Book: iminfo(‘PictureGray.jpg’); • To hand in: the 3 images (rgb, grayscale, and indexed rgb)

  9. Spatial Data • Raster data: Digital Elevation maps • ETOPO1: 1 arc minute resolution • GTOPO30: 30 arc seconds (~1 km) resolution • Shuttle Radar Topography Mission (SRTM) 30, 90 m res.

  10. Spatial Data • Raster data: ETOPO1 • http://www.ngdc.noaa.gov/mgg/fliers/01mgg04.html • Custom grids- ngdc • Your grid ID: you pick a name, likemygrid01 • Grid databas: ETOPO1 • Latitude 30 E 60E Longitude20N 20 S • Grid Cell size 1 min • Grid Format ASCII raster • SUBMIT • w/software, w/ geography, w/coastline • Compress and retrieve • …wait while it processes…. • Retrieve • …wait while it downloads…. • Save your data in a folder that matlab sees • decompress (unzip)

  11. Spatial Data, con’t • Let’s look at the data and header info • On command line of terminal window type • !head MyGrid01.asc (or whateer the name of your data) • You are now viewing the first few lines of the data that you imported • You want to plot the data, so you have to remove the header info from your data file: NewMyGrid=dlmread(‘MyGrid.asc’,’’,6,0); • Now save your new data file save newMyGrid.matNewMyGrid • Now follow the directions from page 169-171 • With the same data, modify script on page 172

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