Lab #5 ppt

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 Vector data- making polygons, outlines, like coastline
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Raster data, 2D arrays, gridded data
Color, or rainfall, or elevation
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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…
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24-bit system; 8 bits for each RGB
channel=2563=16,777,216 colors
24 bit storage requires lots of memory!!!
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Compuserve Graphics Interchange Format (GIF):
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Microsoft Windows Bitmap Format (BMP)
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256 colors, Compression without data loss-Designed for fast transfer over the internet,
Good for line art, simple maps, cartoons, logos
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
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PICT
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Apple; Rasters and vectors; PICT not supported by other platforms
PostScript (PS) Encapsulated PostScript (EPS)
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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
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Joint Photographic Experts Group (JPEG)
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Image compression and format; Irreversible compression (data lost); Three
channel- 24 bit true color
Portable Document Format (PDF)
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Adobe; Cross-platform; Contains complete formatting of vector illustrations,
raster images, and text; Highly compressed; Fast internet download
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http://asterweb.jpl.nasa.gov/gallerymap.asp
Make new directory in your matlab space
Download and save image
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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)
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Raster data: Digital Elevation maps
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ETOPO1: 1 arc minute resolution
GTOPO30: 30 arc seconds (~1 km) resolution
Shuttle Radar Topography Mission (SRTM) 30, 90 m res.
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Raster data: ETOPO1
http://www.ngdc.noaa.gov/mgg/fliers/01mgg04.html
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Custom grids- ngdc
Your grid ID: you pick a name, like mygrid01
Grid databas: ETOPO1
Latitude 30 E 60E Longitude 20N 20 S
Grid Cell size 1 min
Grid Format ASCII raster
SUBMIT
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w/software, w/ geography, w/coastline
Compress and retrieve
…wait while it processes….
Retrieve
…wait while it downloads….
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Save your data in a folder that matlab sees
decompress (unzip)
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Let’s look at the data and header info
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On command line of terminal window type
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!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.mat NewMyGrid
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Now follow the directions from page 169-171
With the same data, modify script on page 172

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