Page 1Page 2Page 3Page 4Page 5GEO/EVS 425/525 Unit 5Overview of Vector ImagesSo far in this course, you have concentrated on raster images. In this exercise, you will deal with severalsorts of vector images and explore the differences between raster and vector images.Vector images represent objects, just as raster images represent space. Vector objects do not need totake up all of the space in the image (although they may), just as raster images to not need to distinguishspecific objects. All vector images are stored in Arc/Info Arc Coverage format by ERDAS Imagine. There are three types of vector coverage: Point, Line, and Polygon. Point vectors are just that – theobjects represented are individual points. Line vectors are polylines: they begin and end at nodes, andstraight line segments connect the nodes via intermediate vertices. A given line may connect thousandsof points, but it remains a line. Polygon vectors are irregular polygons of various sizes. Typically theyare formed from lines which intersect at nodes. A polygon may be formed by a single line which beginsand ends at a single node, or it may comprise many lines in which one line begins at a node whereanother ends. Typically, points, lines, and polygons are handled in separate files, but they need not be. Obviously, point vectors and line vectors cannot even begin to express all of the space in an image. Polygon vectors can, but they often do not.The statement that “all vector images are stored in Arc/Info Arc Coverage format by ERDAS Imagine” isdeceptively simple. The Arc Coverage format is fairly complex, and each image constitutes several filesin two directories. As a result, you have to use some special tools to deal with vector files. These arefound in the buttons under the “Vector” icon on the main Imagine Control Panel. To operate on vectorfiles in Imagine, you MUST use these tools. Point VectorsCopy the SHSCHOOLS vector file into your X: drive and then open it. To copy a vector file, you mustuse the vector tools built into Imagine. Click on the “Vector” button on the main Imagine Control Paneland click on “Copy Vector File.” Your input file is Q:SHSCHOOLS; your output file is X:SHSCHOOLS.When you have copied the file on your X: drive, open the point vector file SHSCHOOLS. Rememberthat vector files are stored in Arc Coverage format; their icons are fuzzy green things. This image showsthe locations of all schools in the Shaker Heights, Ohio quadrangle. Let’s make the points easier to see. Click on Vector-Viewing Properties. Note that “points” is checked, and that the default “point” designatoris a small blotch. Click on the pop-up to the right of the blotch window, and choose “other” from thechoices presented to you. Click on the black filled circle, and then click on the pop-up to the right of theblack color blotch at the right of the window. When the color palette opens, pick an interesting color (butnot black, yellow, or blue). Then change the size of the circle from 2.0 points to around 4. Click on OK. When the window closes, click on “Apply” in the Viewing Properties window. What happens to thepoints?Note that the Viewing Properties window has no “OK” button. It will remain open until you click on the“Close” button, to let you design an image that is easiest for you to interpret. When you like the nature ofyour dots, click on “Close.” You are asked whether you wish to save the symbology to a file. Choose todo so. When naming your file, you have two choices: to give the symbology the same name as the fileand to give it a different name. Give it the same name: SHSCHOOLS.EVS. Note that you have to typein the “.EVS”. If you don’t, the program will go into the SHSCHOOLS directory and invite you – again –to pick a name. You want the .EVS file on your X: drive. Use the eraser icon to remove the file from your viewer. Now open it again. The dots are as youchanged them, because when Imagine finds a symbology (*.evs) file in its vector working directory withthe same name as a vector file being loaded into a viewer, it automatically uses the symbology file.Let’s look some more at the symbology file. In the viewer, click on Vector-Symbology. The symbologywindow opens, but it contains no records. Click on Automatic-Unique Value. This will create a uniquesymbol for each item you choose. The Unique Value dialog opens, asking that you select an attribute touse for the symbology value. Choose “Board", which indicates the school system to which the school inquestion belongs. Check the “Generate New Styles” box to generate the new symbols, and click OK. The symbology dialog fills with the newly generated styles. When you click “Apply”, these symbols areapplied to the viewer. Pick one of the school systems. Click on its row number in the “Row” column toselect the record. The record will turn red. Click on the symbol. The symbol dialog opens. Click on“other.” When the Other dialog opens, click on “filled black circle”, change the color to something morestriking than it currently is, and increase the size a couple of points. Click on OK and Apply. Whathappens to the dots? Now right-click in the “Row” column of the symbology table to bring up the hidden functions. Select Allrows. Then click in the symbol field of one of the rows to open the symbol dialog. Again click on “other”. When the Other dialog opens, click on the popup beside the “Menu” field to open the various menusavailable to you, and choose USGS. Within the USGS menu, choose the school symbol. Increase itssize to about 10 points or so, click on OK and Apply. What happens now to the dots? Again click on therow column of one of the school systems to select it, then click on the symbol field, then “other”. Changethe color to something more striking, then click on OK and Apply. Close the symbology dialog. You will be asked if you want to save it. Choose to do so. You don’t needto choose a name, since you are saving the new symbology to the default location of the image in yourviewer. Erase the SHSCHOOLS image from the viewer and then reload it. Your new symbology isautomatically used. Line VectorsLoad the SHSTREAMS file from the Q: drive into your viewer. Within Vector Options, choose to Clearthe Viewer so that only the streams file is there. This is an image of the hydrologic objects in the