Transcript Lab #5 ppt
Vector data- making polygons, outlines, like coastline Raster data, 2D arrays, gridded data Color, or rainfall, or elevation 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!!! Compuserve Graphics Interchange Format (GIF): Microsoft Windows Bitmap Format (BMP) 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 PICT Apple; Rasters and vectors; PICT not supported by other platforms 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 http://asterweb.jpl.nasa.gov/gallerymap.asp Make new directory in your matlab space Download and save image 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) 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. Raster data: ETOPO1 http://www.ngdc.noaa.gov/mgg/fliers/01mgg04.html 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 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) 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.mat NewMyGrid Now follow the directions from page 169-171 With the same data, modify script on page 172