Digitizing Data

Power On and Log In

Plug in the black block plug from the GTCO digitizing table into the wall.  You will note 4 sharp beeps and the lights on the GTCO pointing device (the "puck") will illuminate.

Logon at GEOS-09 (to the right of the digitizer) using your BEDROCK account and password.  A standard desktop will come up.

Initialize AutoCAD Map

Double click the AutoCAD Map icon.  The layout on the screen for this application is fairly complicated.  AutoCAD Map does have a lot of bells and whistles that we won't be using now -- don't let the complicated menus blow you away -- we will only be using a few commands.  The two windows we will be using today are the big black window (the drawing window) and the short wide white window (the text window) at the bottom of the screen.

AutoCAD Map is configured to start off with some useful wizards.  Click the "Start from Scratch" wizard button, select metric units. If you find floating menu bars cluttering up the windows you are using just drag them up to the top toolbar where they'll be out of your way.

One of the very powerful features of AutoCAD Map is its ability to create drawings in any of the common coordinate systems (geodetic or UTM systems using any of the commonly available datum's).  Because of this flexibility we need to specify the coordinate system before we start our map session.

Set Coordinate System

For this project we will be using the Fairbanks D-2, SW quadrangle (revised 1992).  Note (in the lower left hand corner) that this map is based on the North American Datum of 1927 (NAD27) and the 1000 meter grid used on this map is based on Zone 6.

From the Map … Map Tools pop-up menu select Assign Global Coordinate System

In the Assign Global Coordinate System Code dialog box click codes.  In the Global Coordinate Systems dialog box select the UTM - NAD27 category.  Next, from the Available Global Coordinate Systems window select NAD27 Universal Transverse Mercator, Zone 6 North, Meters.  The coordinate system code should read UTM27-6.  Click OK for the two dialog boxes.

Calibrate Digitizer

Note that the digitizer is initially uncalibrated, and we have to tell AutoCAD Map the UTM coordinates for a number of points on the map.  A minimum of two points are needed to calibrate, however 3 or 4 points will allow the program to adjust for shrinkage of a paper map.  Pick 4 points that enclose the features to be digitized and for which you can easily determine the UTM easting and northing in meters.  For example: 458000,7194000; 458000, 7192000; 462000, 7192000; 462000, 7194000 (On the Fbks. D-2 SW).

Tape your map down with drafting tape, be sure to use temporary tape.  The digitizer surface is delicate and we want to maintain its smooth surface.  The table can be damaged by denting, cutting, or scratching off old tape. Use only drafting tape and remove tape after use.

Note that the mouse and the puck are both active pointing devices.  Use the mouse to control the program and the puck to point at locations on the map.

From the Tools … Tablet pop-up menu select Calibrate.  Down in the white text window the program will prompt you for point #1.  Move the digitizing puck's crosshairs over the calibration point and press "0" on the puck.  The text window will prompt you for the coordinates of point #1; enter the easting and northing of point #1 separated with a comma followed by the enter key.  For example: 458000,7194000 <enter>.

The program will prompt you for point #2, continue with all 4 points.  Press <enter> when asked to digitize the 5^th point.  The program then generates statistics for the calibration.  If the residuals are "small" (how accurate do you want your map to be? Residuals ~ 10 meters would be reasonable for a 1: 25000 map).

The program now asks you if you want to accept the calibration -- if the residuals are acceptable then choose the orthogonal calibration <type "o">.  If the residuals are not acceptable type <escape> and start the calibration routine again.

If the paper shifts or if you close AutoCAD Map then you will need to recalibrate.

After Calibration

Note that if you move the puck over the calibrated area, the cursor in the black drawing window disappears and if you move the mouse the cursor reappears in the drawing window.  Note also that as you move the mouse around in the drawing window the coordinates (easting, northing) are small numbers (much smaller than the calibration point values).  This is because the drawing window is zoomed in on a very small window near the origin (easting =0, northing = 0).  If we want to view our digitizing as it progresses, we must move the view of the drawing window to values typical for the area we are digitizing.

Zoom in on digitizing area

To zoom to the digitizing area we will draw a rectangle around the area of interest and then fit the extents of that rectangle to the drawing window.  From the menu bar, click on draw … rectangle.  Note that the text box is prompting you for the first corner of your rectangle.  Move the puck to the northwest corner of the calibration rectangle, press "0" on the puck.  The text box is prompting you for the other corner of your rectangle.  Move the puck to the southeast corner of the calibration rectangle, press "0" on the puck.  You have drawn a rectangle around your project area - however, at present, AutoCAD Map is zoomed in on an area by the origin where nothing has been drawn.  This is such a common problem that AutoCAD Map has a command that automatically zooms to fit all of the drawing objects into the drawing window.  From the menubar select view … zoom … extents and the drawing box will be centered on the calibration rectangle.  Move the puck in the calibrated rectangle on the map and you'll see the cursor move within this rectangle on the computer.

You will want to decide whether you are drawing points or drawing shapes consisting of connected points (in AutoCAD Map jargon, "polylines").  When done, save your drawing: File … Save to your userspace on BEDROCK.

To draw polylines

Say you want to digitize the location of a geological contact.  Select Draw … Polylines.  Move the cursor over one end of the contact, click "0".  Then move to the next point on the line (depending on how you want to represent the line the next point could be a millimeter away or 10 centimeters away), click "0", and you can watch the line appear on the monitor.  To stop the process, take your cue from the text screen which has prompted you:

Arc/Close/Halfwidth/Length/Undo/Width/<Endpoint of line>:

Ignore the first 6 choices, the default choice (what you get if you don't specify otherwise) in AutoCAD Map is always shown in brackets like  <   >.  Press enter to accept the default <endpoint of line>.

Repeat this for as many lines as you want.

To draw points

Say you want to digitize the location of an observation or a sample which has been located on the topographic map.  Select Draw … Points … Multiple Point.  Move the cursor over your first location, click "0".  Then move to the next point, click "0", and you can watch the points appear on the monitor.  To stop the process, press the escape key.  The default point plots as a single pixel.  To change the plotting symbol go to Format … Point Style on the menubar.

Repeat this for as many points as you want.

Exporting the drawing to CorelDraw

AutoCAD Map is very powerful, however sometimes its user interface is overwhelming.  It is also very expensive piece of software (that's why the department only has two copies.  For these reasons, people often want to move to a more friendly, cheaper drawing program such as Corel Draw.  To do this, export  your drawing in the encapsulated postscript format (extension is .eps).  This is a format which is very readable by many different graphics packages (including Corel v.7 - v.8) and is distinct from the ACAD drawing file format (extension is .dwg).  From the menubar select File … Export.  Under save as type:  Select Encapsulated PS (*.eps) and pick a file name and location in your userspace.

In CorelDraw (ver. 8), select File … Open and select the *.eps file which contains the digitized data.  Note that the units in Corel Draw do not reflect UTM coordinates of the objects.  This is one of the tradeoffs with CorelDraw -- it is a lot less picky about scales and units and other details which make AutoCAD complicated.

All is not lost however, using the calibration box we digitized from the map one can properly scale the Corel drawing.  As imported into Corel, all of the objects are grouped together into a single group.  If we scale the calibration box (be sure no objects extend beyond the box), then the objects will be scaled properly.

For the class example the calibration box is 4km EW and 2km NS.  From the Tools menu select Options.  This Options Dialog is the central location for modifying the properties of a CorelDraw drawing.  Expand the Document heading (click once) and select Rulers.  Set the horizontal units to kilometers (do not uncheck the same units for horizontal and vertical rulers).  Click Edit Scale.  Set the page distance to 1 centimeter, and set the world distance to 0.25 kilometers (Scale in CorelDraw will be 1cm = 4km).  Click OK twice and your back to your drawing.  Now the paper is scaled, but we need to make the scanned-in calibration box the correct size.

Click on your drawing once and note that a number of little black shapes appear around the drawing objects (these are called handles).  Look up in the upper left hand corner (in the menu bar) and you'll see 6 white boxes with numbers in them labeled x:  y:, width height (indicated by arrows), and %.  X: and y: are the coordinates of the center of the group of objects that comprise your object, the arrow symbols indicate the dimensions (in scaled units), and the % values indicate scaling factors for height and width.  To properly scale your map simply set the width and height of the group to the e-w and n-s dimensions of the scale box.

Exporting the UTM coordinates of the digitized objects

Points

From AutoCAD Map select the points for which you want coordinates by clicking once on them with the mouse (when they get a blue "halo" it means they are selected).  If you to select a flock of points then click once to one side and above or below them and drag (hold down the mouse button the selection rectangle over the points you want to select.  Once you have your points selected then Click  Quicksurf … Export Data … Entity XYZ.  The Text box will prompt you for a file name, enter something like n:\points.txt.  The file will contain the easting, northing, and elevation of the points.  Elevation will be zero unless you specified it somewhere else.

Lines

Usually you won't want the coordinates for points on a polyline, it is possible however:  In AutoCAD Map select the polyline for which you want coordinates by clicking once on it with the mouse (when they get a blue "halo" it means they are selected).  At this point if you export XYZ you will get the coordinates of the center of the object.  If you really want the individual UTM coordinates of the clicked points on the polyline you must click Tools … Inquiry … List.  This will generate a text dialog box in which you can view the points.  To move the points to a text file, select the text data and copy and paste them into a text editor.  You can clean up the extra characters in notepad, excel, etc.
 

Revised January 2001
 

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Last modified August 3, 2006 by geology@uaf.edu