- Prepare the map: Specify at least four control points whose exact coordinates you know. Mark them with a pencil and assign a number to each. Calculate their coordinates in decimal degrees. For example 90° 45' = 90.75. Pay attention that locations west of the 0 meridian are negative. Fix the map to the tablet with a masking tape.
- Turn on the digitizer tablet
- Restart the computer
- Open CalComp (Start / Programs / CalComp) to assign certain functions to the puck's buttons. Ensure that you have at least specified one button each for "left", "left double", "right" and "middle double" click. I usually assign the following buttons: 0 = "left click" 1 = "left double" 2 = "middle double" 3= "right" Do not close CalComp
- Open ArcVIEW
- Activate the Digitizer Extension (File / Extensions: checkmark Digitizer)
- Create a new View and specify its properties (View / Properties). The Projection in our case it's mostly "UTM" - "zone 14"
- Digitizer Setup (View / Digitizer Setup)
- Click on the puck icon
- Set units to "decimal degrees"
- Move the puck over the tablet and click once with the button that was specified before as the left-click (see above under CalComp). If the cursor works like the mouse (so called relative mode) press F2. If it works like a digitizer (absolute mode) don't change anything. (Remember: you can always switch between these two modes with F2)
- Click once exactly at the first control point of the paper map. Click once at the second point, at the third point etc. until you have at least four control points.
- Use the real mouse again, click in the field for the X-value of the first control point and type in the exact coordinates for each control point.
- If you did everything well the calculated error should be below the default value of 0.004 in. If so, save these points for further digitize-sessions and click on register. If not, re-digitize some or all control points. (By the way: the reference points and lines in the "geo-....shp" files are are digitized with an error of 0.0017 in)
- Create a new theme (View / Create a new theme), chose a theme-type ("point", "line" or "polygon") and specify the path and the filename for it.
- If the puck is in the absolute mode press F2. If it's in the relative mode don't change anything.
- Zoom in to your area of interest by activating the Zoom-in Icon
-
Click with the
puck a little left
and a little below the bottom-left corner of your area of interest of the
paper map.
- Click with the puck a little right and above the top-right corner of your area of interest of the paper map.
- Press F2
- Click on the drawing tool you need (see examples on the right)
- Press F2
- Finally: Digitize and enjoy it. If you are drawing a line or a polygon your last point has to be a left-double-click (whatever button you have specified to this function).
- Press F2
- Theme / Stop editing and save your new file.
- If you want to create another theme start again with Create a new theme.
2) Tracing lines or points of a scanned image directly on the screen
- Scan your map - all the scanners in Sutton Hall Computer Lab are hooked up to an Apple Macintosh
- Open Photoshop (Apple-Symbol / Applications / Photoshop)
- Click on File / Import / Scannername
- Click on Preview
- Specify whatever you want. Some rules of thumb: reflective, scale=100%, resolution=300 dpi, color=24 bit RGB
- Click on Scan and wait
- Save the image in the "TIFF" file format and if asked for a computer type chose IBM PC (do not activate the LZW compression)
- Close Photoshop
- Open Fetch (Apple-Symbol / Networking / Fetch)
- Connect to "mather.ar.utexas.edu". Username = anonymous, Password = your@emailaddress
- Specify the target folder (normally "pub\temp2weeks\")
- Click on Put, chose the file you want to transfer, chose "raw data" and click OK
- Wait until file transfer is complete
- Close Fetch
- Go to a PC
- Open WS_FTP (Start / Networking / WS_FTP). Help for FTP
- Connect to "mather.ar.utexas.edu". Username = anonymous, Password = your@emailaddress
- Specify the target folder in your local system (= left part of the window)
- Go to the source folder in the remote system (= right part of the window)
- Since you want to transfer an image click on Binary (the middle toggle at the bottom)
-
Click on the arrow from right to left in the middle
- Close the connection and exit
- Open ArcVIEW
- Open the project with the already geo-referenced shape-files in it (e.g. the shape-files you have created before with the digitizer tablet)
- Activate the "Image Analyst Extension" (File / Extensions. checkmark "Image Analyst")
- Add a theme (click on the big Plus Icon or: View / Add a theme), chose "Image Analyst File" as file type and go along the path to the TIFF file. Highlight it and open it.
- Make the new TIFF-Image visible (that is, checkmark it) and move it to the bottom of all your layers (just drag and drop)
- Zoom in to the area where the new TIFF-Image should appear.
-
Activate the theme with the TIFF-Image (just click on it once)
- Click the Align Tool once and be surprised!
- Zoom in to the area of a point which you can easily distinguish in both the TIFF-Image and in one of the already geo-referenced shapefile themes. Good points for this purpose are road intersections etc. (let's call such a point 'common point').
- Activate again the Align Tool and click on the first 'common point' on the TIFF-theme then click on the same point in the shapefile-theme. Do the same with as many other 'common points' you can find until you like the result. This procedure is also called "rectifying" or "rubber-sheeting".
- Now that your scanned image is aligned properly you can create a new theme (View / Create a new theme) by tracing along any line or point of the scanned image as you see it on the screen.
- If you want to keep the TIFF image in the rubber-sheeted position you have save it explicitly: Theme / Save image
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6 October 2000
The School of Architecture at UT Austin
Comments to: Barbara Parmenter