IMAGES, SPATIAL DATA AND MATLAB

Data types and storage:

Vector data- making polygons, outlines, like coastline

Raster data, 2D arrays, gridded data

Color, or rainfall, or elevation

Data types and storage:

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!!!

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

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

Importing, Processing, Exporting Images

lab activity:

http://asterweb.jpl.nasa.gov/gallerymap.asp

Make new directory in your matlab space Download and save image

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)

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.

Spatial Data 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)

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.mat NewMyGrid

Now follow the directions from page 169-171 With the same data, modify script on page

172