GY301 Geomorphology: Notes on Using DraftSight CAD for Constructing a Closed Traverse (Lab 1)
Introduction
Computer-Aided Design applications (AutoCAD, DraftSight, etc.) are often used to construct maps in the geosciences because of the multitude of precise drafting “tools” and the ability to easily edit existing drawings and plot hard copy maps to large-format plotters and printers. The ability to easily re-use existing maps and rapidly output multiple copies is another advantage. If you learn to use CAD applications you will find that skill very useful in future labs in GY301 and also other Geology courses, especially GY403 Structural Geology and GY480 Field Geology. Several students have completed their entire geologic map and cross-section GY480 project with CAD applications (DraftSight). For this example we will use DraftSight because it is free public-domain software and it is almost 100% compatible with the most popular CAD application AutoCAD. The below steps will take you through the process of constructing the GY301 Lab 1 closed traverse map. You will need to have your groups distance and azimuth values that were measured between the trees of the pace and compass course.
Step 1: Download and Install DraftSight Application.
Follow the directions in the below web site:
Note that you can also download DraftSight for a Mac or Linux system. Make sure that you match the 32 or 64 bit version to your operating system.
You will be asked to provide an email address after installing and running the application for the first time. I recommend using your USA email address. We have not had any problems with the parent company (Dassault Systems) misusing the contact information. They will periodically send you unsolicited emails but they are reasonably rare.
Step 2: Setting up the Drawing File.
After starting DrafSight you will see a blank drawing file window. Go ahead and select “File > Save As” to save the current drawing to a file. Use a meaningful file name like “GY301_Lab1”. The application will automatically append the standard file extension of “.dwg”.
The next procedure establishes the polar coordinate system that you will be using for the drawing. By default DraftSight initially uses “mathematical” polar coordinates with the 0 angle aligned with the positive x axis (east), and angle degrees increase in a anticlockwise direction. Therefore 90 would be aligned with the positive y axis (north), 180 the negative x axis(west), and 270 with the negative y axis (south). In the earth sciences we normally want to use azimuth angles:
0 = North, 90=East, 180=South, 270=West
To set azimuth angles use the menu sequence “Format > Unit System”. In the activated window set the “base angle” to 90, and check the “clockwise” checkbox. From this point on all angles used in the drawing will conform to the azimuth system. This is saved with the file so you should not have to reset the base angle again unless you want to switch to another angle system.
NOTE: there are some commands in the DraftSight system that use “mathematical” polar angles no matter the situation. If you find that angles are not aligning properly this is probably the cause so you may have to revert back to mathematical angles until those commands are processed.
To make sure that your map fits within the bounds of an 8.5 x 11.0 inch media it is a good idea to establish reasonable boundaries. Remember that your scale is 1 inch = 100 feet, so if you are going to work with “real world” units there should be 100 units (i.e. feet) per plotted inch when the map is printed. In reality the printer can’t actually print to the absolute edge of the paper so we will build in a “hardware” margin of 0.25 inches all the way around a letter size sheet of paper in portrait orientation, therefore, the “paper” rectangle is 800 by 1050 units. To construct this media edge follow the below steps:
- Use the “Format > Layer” menu sequence to create a new layer named “Paper” and make it the active layer. Assign it a color of light gray.
- Use the “Draw > Rectangle” menu sequence with the following input arguments:
: _RECTANGLE
Options: Chamfer, Elevation, Fillet, Thickness, line Width or
Specify start corner»0,0
Options: Area, Dimensions, Rotation or
Specify opposite corner»800,1050
{Note: the only numbers that I typed are in red}
At this point the paper media margin will be drawn but you are “zoomed” in so that you cannot see the full extent. Use the menu sequence “View > Zoom > Bounds” - you should now see the full media “rectangle”. When you construct the closed traverse you will want to keep all elements of the drawing inside the “paper” rectangle, otherwise they may not plot.
Step 3: Draw the Original Traverse Data
To complete this step you will need to have your azimuth and distance station-to-station data on hand for the drawing commands. Using “Format > Layer” create a new layer named “traverse” and make it the active layer. Leave the color to the default of “white” (which is actually a black color). Now use the “Draw > Polyline” command to begin the traverse:
_POLYLINE
Options: Enter to continue from last point or
Specify start point»{start with a left-click}
Options: Arc, Halfwidth, Length, Undo, Width, Enter to exit or
Specify next vertex» @153<19
Options: Arc, Close, Halfwidth, Length, Undo, Width, Enter to exit or
Specify next vertex»@138<42
Options: Arc, Close, Halfwidth, Length, Undo, Width, Enter to exit or
Specify next vertex»@235<153
Options: Arc, Close, Halfwidth, Length, Undo, Width, Enter to exit or
Specify next vertex»@205<210
Options: Arc, Close, Halfwidth, Length, Undo, Width, Enter to exit or
Specify next vertex»@318<156
Options: Arc, Close, Halfwidth, Length, Undo, Width, Enter to exit or
Specify next vertex»@257<214
Options: Arc, Close, Halfwidth, Length, Undo, Width, Enter to exit or
Specify next vertex»@291<316
Options: Arc, Close, Halfwidth, Length, Undo, Width, Enter to exit or
Specify next vertex»@222<12
Options: Arc, Close, Halfwidth, Length, Undo, Width, Enter to exit or
Specify next vertex» @217<6
Options: Arc, Close, Halfwidth, Length, Undo, Width, Enter to exit or
Specify next vertex»@227<12
Options: Arc, Close, Halfwidth, Length, Undo, Width, Enter to exit or
Specify next vertex»<enter>
The red text above are the responses to the polyline command prompts. Note that the polyline command is terminated with the <enter> key. The “@” sign in the above coordinates indicated that the next polyline vertex is relative to the previous point. The coordinates are in polar format:
{distance} < {angle}
Because we setup the drawing to use azimuth angles we can also use them in the polar coordinate specification.
The traverse should now be constructed but you are probably zoomed in too far to see all of it. Use the menu sequence “view > zoom > bounds” to zoom to the bounds of the drawing. You should now see all of the traverse.
Step 4: Draw in the Error Vector
The next step will construct the error vector and divide it into 9 equal segments. We need 9 segments because the traverse contains 9 “legs”. The 1/9 segments will be used later to systematically distribute the error so that a corrected perfectly closed traverse can be plotted.
At this point use the “view > zoom > window” and draw a window around the first and last vertex of the traverse. Right-Click on the bottom center tab named “esnap”. Select “settings” and make sure that only “enable entity snaps” and “end” is checked. This means that if you left-click near a vertex of a polyline the point will snap exactly to that point. Now create a layer named “error_vector”, color it red, and make it the active layer. Use “draw > polyline” to draw a line from the last traverse vertex to the 1st traverse vertex. Add a small polyline to make a simple arrowhead on the end of the error vector at the 1st traverse point.
Next, to divide the error vector into ninths use the menu sequence “Draw > Point > Mark Divisions” to place “points” at equal divisions along the length of the line. Indicate 9 divisions:
: _MARKDIVISIONS
Specify entity»{selectline with a left-click}
1 found
Default: 2
Options: Block or
Specify number of segments»9
The point objects are difficult to see because by default they are just a single pixel size. To make them more visible use “Format > Point Style > Points” to use a more visible symbol such as a circle with a centered cross. A size of 1 foot should be visible. Note that the “MarkDivisions” command inserts only 8 point objects on the line to mark the 9 divisions. In effect the end of the line is also the end on the 9th segment. In the future if you want to be able to snap to either a point object or the end of the error vector line you would want to use both “node” (point objects) and “end” (line objects) entity snap modes.
Step 5: Copy the Error Vector and Construct Adjusted Traverse
Do a “View > Zoom > Bounds” and then a “View > Zoom > Window” to zoom to the area that shows the error vector and the second traverse point. Use the “Modify > Copy” menu sequence to start the copy command:
: _COPY
Specify entities»wi
Specify first corner»
Specify opposite corner»
10 found
Specify entities»<enter>
Default: Displacement
Options: Displacement or
Specify from point»{snap to tail of error vector}
Options: Enter to use first point as displacement or
Specify second point»{snap to 2nd traverse point}
Default: Exit
Options: Exit, Undo or
Specify second point»<enter>
Note: the above assumes that the entity snap is still on, and that one of the entity snaps is “end”. Check this before using the copy command.
This should place the tail of the error vector precisely on the 2nd traverse point. Now create a new layer named “corrected” and color it blue. Change the “snap entities” to include “node” and “end”. The “node” snap allows you to snap to a point object. Draw a polyline from the 1st traverse point to the 1/9 segment of the error vector at the 2nd traverse point. Repeat this process until the corrected traverse is complete.
Step 6: Formatting for Plotting
In this step we will center the drawing and add a north arrow and scale bar. Finally, we will send the map to a printer for hard copy output.
Make sure you are zoomed out to “bounds” so you can see all of the map entities. If your traverse has strayed outside of the “paper” rectangle, or if you want to better “center” the traverse inside the media boundary use the menu sequence “modify > move”:
_MOVE
Specify entities»{Left-click on “paper” rectangle}
1 found
Specify entities»<enter>
Default: Displacement
Options: Displacement or
Specify from point»{Left-click anywhere in the drawing window}
Options: Enter to use from point as displacement or
Specify destination»{move the mouse to dynamically see where the rectangle will be moved, and then left-click}
: z {shortcut for ZOOM}
ZOOM
Default: Dynamic
Options: Bounds, Center, Dynamic, Fit, Left, Previous, SElected, specify a scale factor (nX or nXP) or
Specify first corner»e {shortcut for extents or bounds- will show all of drawing on screen}
You may need to try several “moves” to get the traverse centered as you wish.
Next, let’s make a north arrow. Legend items such as north arrow usually require a snap grid- this is a setting that forces the cursor to move up, down, left, or right in discrete increments. Because the scale is 1 inch = 100 feet and I wish to move around in 0.1 inch increments the snap will be set to 10 feet. Use the bottom center “Grid” and “Snap” buttons to set a 10 unit grid and snap. Next, use the “limits” command to make grid and snap apply over the entire drawing area:
: limits
DRAWINGBOUNDS
Default: (0.0000,0.0000)
Options: OFf, ON or
Specify lower left corner»{snap to lower left corner of “paper” rectangle}
Default: (12.0000,9.0000)
Specify upper right corner»{snap to upper right corner of “paper” rectangle}
:
The grid should now appear throughout the drawing area. You may have to zoom in to see the grid points. Note that the grid nodes will not print with your drawing.
Now zoom to the upper right corner of the drawing. Create a new layer named “Legend” and color it “white” (actually black). Make this the active layer. Proceed to draw a simple upward (North) point arrow with the polyline command:
Note how the cursor “jumps” to 10 unit increments making it easy to draw a perfect arrow. Now use the menu sequence “draw > simple note” to add a “N” at the base of the arrow:
: _SIMPLENOTE
Active TextStyle: "Standard" Text height: 0.2000 Annotative: No
Options: sEttings or
Specify start position»{left-click below arrow}
Default: 0.2000
Specify height»20
Default: 90
Specify text angle»<enter>
Note that we used 20 units for the text height (0.2 inches plotted). If the “N” is not aligned properly with the arrow left-click on it to highlight, then grab the blue “handle” and drag it to the correct position. Note that the “snap” is still in effect so the “N” jumps at 10 unit increments.
The next step will create a scale bar. Zoom window to an area at the bottom of the drawing and centered under the traverse. Use the polyline command to draw a line precisely 100 units (10 grid dots) long with tic marks on each end. Use the “Draw > Simple Note” command to add the label “0” at one end and “100 feet” at the other end of the scale.
Lastly, we will plot a hard copy of the drawing. If you are connected to a printer at this time make sure it is ready. If not you can output to a PDF file for printing at a later time. Because the “paper” layer is used only for centering the traverse let’s make it “non-printing” with the “Format > Layer” menu sequence.
Use the menu sequence “File > Print” to get tothe main print setup dialog window. These are the important settings that you must change:
- Printer/plotter name: select the name of the desired output device.
- Paper size: ANSI A (8.5 x 11 inches).
- Print Scale: uncheck the “Fit” option and then set 1 plotted inch = 100 units.
- Print Range: all geometry
- Geometry orientation: Portrait
- Print offset: uncheck the “center” option and make sure X and Y offsets are 0.0
At this point do a “Print Preview” before selecting the “OK” button. If the preview looks OK go ahead and plot, if not cancel the print and adjust the drawing so that everything fits.