Lab #2

Traverses

Preparing for this Lab

Read over the lab in advance.  Make sure you understand what you should bring.  If weather is inclement check with the instructor in advance.  Do not assume class will be cancelled.  Switching a lecture and proficiencies session indoors for a lab outdoors is an option.  Do not assume class is cancelled unless the University is shut down. 

Review the procedures for the lab.  Review the suggested style of taking notes.

What Will I Be Doing in this Lab

You will be doing a traverse around the Engineering Building.  During the traverse you will obtain the locations of the corners of the Engineering Building using sideshots.  You will work in two groups.  Groups will go in opposite directions around the building and meet (we hope) on the back side.  This is an example of a "Closed Traverse" in that the traverse essentially loops completely back to the point of beginning.  A "Closed Traverse" furnishes an accuracy check because obviously after going around the building the point of beginning should have the same coordinates when you finish as it did when you started.  You will use two class periods to do this work (and it will take every bit of that).  During this lab you will frequently switch instruments that you are using for your surveying so that each crew will get to traverse using a variety of instruments.  The exact instruments you will use will be determined based on what instruments you have been introduced to which will in turn have been influenced by the previous weather and how often we have been forced indoors.

What You Will Need

(Things Provided by the Department and Instructor)

1- Transits, Theodolites, and Total Stations compatible with your training to this point (because of slippage lectures for bad weather you will not all have the same equipment each year).

2- Wood Stakes

3- Nails

4- Hammer

5- A Philadelphia Rods, Reflectors, survey markers as appropriate

(Things You Should Bring)

1- Clothing compatible with cold, rain, wind, sleet, or snow (unless the weather and forcast clearly indicate you will not need them)

2- Paper for writing down survey notes including some sort of backing to make the paper rigid enough to write on.

3- A writing instrument

4- A tape measure at least 6 feet long.

5- A magnifying glass (or a very very good set of eyeballs - for reading transit vernier)

What You Will Do - Detailed Instructions

(Work to be done by both survey crews)

Go to the north side of the Engineering Building near the east - around where the funny looking blue artwork thingy is located.

Pick a point around the north east corner of the E wing of the Engineering building that affords a good view going both west and south around the Engineering building.  Set up the transit or theodolite provided to you by the instructor.  Stake the location.  Measure the height of your instrument.

Allow the instructor to step in a take a GPS reading on your position.  The instructor will give you an assumed height of your location.  Since you will be keeping track of elevations as well a horizontal coordinates this time you will need this initial elevation (use 440 feet).  The instructor will give you the coordinates of your initial position later.

Backsight the center of the smokestack on the SIU Power Plant.  (This time you will establish the direction of your initial backsight line from known coordinates of two points - ie your initial point and the location of the smokestack.  This is a common modern way of establishing an initial known point and known direction for a survey).  Now foresight a point going west around the Engineering Building.  Pick the spot that you foresight so that an instrument set at that point will have a clear view of the points around the north entrance to the Engineering Building as shown in Figure 1 below.  Have your "Rod Man" hold a Philadelphia Rod at that point keeping it straight up and down.  Sight a point on the rod at the same height as your instrument.  Reading the upper and lower rod intercepts record these entries in your field notebook and calculate the distance to the foresight point.  Record the angle right and the vertical angle - make sure to include a note about which way your instrument used as zero for the vertical angle.  Drive a stake at the point occupied by the "Rod Man".

Now backsight the center of the smokestack on the SIU Power Plant again.  This time turn the angle right to a point across Douglas Drive and in front of the Athletic Complex where you can get a clear view of the corners of the Engineering Building as shown in Figure 2.  Have your "Rod Man" hold a Philadelphia Rod at that point keeping it straight up and down.  Sight a point on the rod at the same height as your instrument.  Reading the upper and lower rod intercepts record these entries in your field notebook and calculate the distance to the foresight point.  Record the angle right and the vertical angle - make sure to include a note about which way your instrument used as zero for the vertical angle.  Drive a stake at the point occupied by the "Rod Man".

You have now set up the first points for the traverse team going west and the team going south around the Engineering Building.  Do Not Pull Up Your Stakes When You Move - These Will Be Your Backsight Points!

(Work to be done by Survey Crew West)

Set up your assigned instrument over the point established by the survey.  Take your height of instrument.  Send your Rod Man (who can be female - Surveys have not yet changed the name to Rod Person) to one of the corners of the building that is viewable from your present point.  For some of the corners the side walk almost blocks the view.  To measure these corners have your Rod Man extend the Rod so that it stands above the level of the side walk.  When you foresight the point you will not be able to center on the same elevation as your height of instrument.  Take your rod reading, upper and lower intercept, angle to the right and vertical angle.  Reapeat this process until you have shot in all the main corners of the building visible from your location (don't worry about little columns by the windows).  (You are establishing the location of the corner points using "side-shots" off a traverse.  Often the location of a point is of interest in a survey but it is not practical to set the instrument up at that point or use that point as a path to the next point.  In these cases surveyors shoot points in off of one of the points on the traverse.  This is called taking a side shot.  In your case on important reason you need to do side shots to get the building corners is that it is not possible to set your instrument up so it is partially inside a brick wall).

After you have finished shooting your building corners in with side shots look for a point further west around the Engineering building where you can shoot in the remaining corners of the west side.  Send your Rod Man to that vantage point.  Again taking a backsight on the original survey point turn the angle right and take the Rod reading, upper and lower Rod intercepts, angle to the right and vertical angle.  Drive a stake in at the location where your Rod Man stands.  (You are now establishing the location of the next point you will occupy.  Soon your present location will be your backsight.  Note that you are working around the Engineering building using one point to help you establish the location of the next point you move to.  You are "Traversing" your way around the Engineering Building).

(Work to be done by Survey Crew South)

Set up your assigned instrument over the point established by the survey over by the Athletic Complex.  Take your height of instrument.  Send your Rod Man (who can be female - Surveys have not yet changed the name to Rod Person) to one of the corners of the building that is viewable from your present point.  Have your Rod Man put his/her Philadelphia Rod up against the corner of the building keeping it a straight up and down as possible.  Take your rod reading, upper and lower intercept, angle to the right and vertical angle.  Repeat this process until you have shot in all the main corners of the building visible from your location (don't worry about little columns by the windows).  (You are establishing the location of the corner points using "side-shots" off a traverse.  Often the location of a point is of interest in a survey but it is not practical to set the instrument up at that point or use that point as a path to the next point.  In these cases surveyors shoot points in off of one of the points on the traverse.  This is called taking a side shot.  In your case on important reason you need to do side shots to get the building corners is that it is not possible to set your instrument up so it is partially inside a brick wall).

After you have finished shooting your building corners in with side shots look for a point further south around the Engineering building where you can get a clear shot of all the points around the little service parking lot on the east side of the building.  Send your Rod Man to that vantage point.  Again taking a backsight on the original survey point turn the angle right and take the Rod reading, upper and lower Rod intercepts, angle to the right and vertical angle.  Drive a stake in at the location where your Rod Man stands.  (You are now establishing the location of the next point you will occupy.  Soon your present location will be your backsight.  Note that you are working around the Engineering building using one point to help you establish the location of the next point you move to.  You are "Traversing" your way around the Engineering Building).

(Work to be done by Survey Crew West)

Move to your new point with your instrument and use your old point as your backsight.  You may have your instrument changed on you at any point.  If we have covered lectures dealing with Total Stations and use of EDMs you may at some point be given the total station and a reflector and be ask to make distance measurements with the EDM rather than using Tacheometry.  The instructor may also come around periodically and take a GPS reading on your position.

From your new location take sideshots to get the locations of as many of the main building corners as you can get from your present position.  When these side shots are complete and recorded look for your next vantage spot.  You can probably get around behind on the west side of the building at this point.  You will be moving into an area with a lot of trees and you should pay attention of whether you can get clear shots of all the corners on the north west half of the building.  You might be picking a point fairly close to the Campus Lake for your next series of shots.  Shoot in the location of your new Foresight point.

(Work to be done by Survey Crew South)

Move to your new point with your instrument and use your old point as your backsight.  You may have your instrument changed on you at any point.  If we have covered lectures dealing with Total Stations and use of EDMs you may at some point be given the total station and a reflector and be ask to make distance measurements with the EDM rather than using Tacheometry.  The instructor may also come around periodically and take a GPS reading on your position.

From your new location take sideshots to get the locations of as many of the main building corners as you can get from your present position.  You also will need to shoot in two special additional positions.  On the south side of the service parking lot, right next to the building is a steel gate over a subterranean level.  Use side shots to shoot in the south east and north west corners of that steel grate (we will use this information at a later date but it is very important that you survey these two points accurately).  When these side shots are complete and recorded look for your next vantage spot.

The next spot you will probably want to occupy will be near the circle drive in front of the Engineering Building.  From this point you can see the entrance to the courtyard, the south side of Engineering C and the east side of the College of Applied Science and Arts.  With the aid of your Rod Man shoot in the location of this point and drive a stake in at that point.

(Both Crews)

Continue working your way around the building shooting in building corners with side shots and progressing to the next point.  When you can see the other survey crew coming around the building the other way coordinate with them to make sure that between your two crews you will have sighted all the relevant points.  Then pick a point between you that both crews can sight to.  Send a Rod man to this intermediate point and have both crews shoot in this location.  If your survey "closes" properly when both crews calculate the X, Y and Z coordinates of this point there will be close agreement as to where that point is located.  Common problems to watch out for that can cause a "Bust" (a bust is a catastrophic failure in closure) include - turning angles left instead of right without a specific note in your field notes - failure to zero your angle reading on your backsight - failure to clamp the lower motion when you turn the angle to the foresight resulting in both the upper and lower motions moving as the angle is taken.

You should leave your stakes in the ground even when you break after the first day.  Driving your last stakes far into the ground is a good idea because it will make it more trouble than its worth for someone to pull them up.  It will also make sure that if the grounds crews need to cut the grass they will not mow your stake (or feel a desire to kill you for damaging their mower).

Comments on this Lab

In real field work the two known points establishing direction usually come from permanents survey markers established by previous precise survey work of others (not a GPS reading and coordinates off a map).  This requires surveys to start from known points that can be sighted and then traverse to a point where they can begin to survey what ever they were interested in.  While such points are available on campus the amount of time to traverse from those points to the engineering building would be prohibitive for the time limits of this class.  This lab none-the less illustrates how one can establish an initial backsight direction from two known points.

This lab also will have you switch instruments frequently - you will even have instruments that read in different units.  This would almost never be done in a commercial survey.  Switching instruments is an invitation for confusion and mistakes in reading and taking notes.  Any systematic errors in an instrument which might be identified and adjusted out becomes an untracable random error when one works with instruments at random.  It should be remembered, however, that one of the objectives of this class is to expose you to a variety of instruments and techniques so that what ever you are ask to work with or do in the future will at least be vaguely familiar.

This lab is also not a perfect example of a closed traverse.  In a closed traverse one works around a loop with the crew returning to the point of beginning.  In this assignment two crews work in opposite directions around the building meeting in the middle.  Thus the point that should have the same coordinates is the point where the crews met (the location of that point should not change depending on which direction someone went to get there).  This variation of "Closed Traverse" is used for the sake of time (a professional surveying crew could easily go around the building in the time allowed but novices will be and should not feel bad about being slow).

Taking Field Notes

While taking notes is important one of the problems you will encounter on this survey is that you will be shooting in the location of a large number of points.  Unless your memory is truly extraordinary (which it is not) you will not be able to remember what point is what when you may not be doing your map until up to three weeks later.   Therefore one of the things you should include in your field notes is a sketch of your survey with the location of each point written in.  This will help you greatly when it comes time to work with your tabulated data in your field notes.

A form similar to the one below is suggested for taking your field notes

Finishing the Lab

The instructor will give you the coordinates of your initial point and the direction of your first backsight line to the smokestack during the second class period of the lab.  Following completion of the lab each crew will provide a copy of their notes to the other crew, explaining (if necessary) their entries.  Each lab crew will submit a drawing of the plan view of the Engineering Building.  This drawing will be to scale and probably done with Autocad.  The drawing will show the coordinates and elevation of each major corner of the Engineering building as well as the coordinates and elevation of each point on the traverse.  For each point on the traverse (not the side shots) the drawing will show the azimuth and length of the line from one station to the next.  The drawing will show how closely the two crews came to finding the point of meeting to be at the same location (ie - how many feet or fractions of a foot are the coordinates from the two crews apart).  The assignment will include copies of the original field notes.  The drawing will be due one week after the lab is completed in the field.

Things You Will Need to Remember

Because of instrument switching you may have angles measured in degrees minutes and seconds, gons, and maybe even mils.  Lab #1 showed you how to convert angle measurement units.

Remember that when you backsight a point that you previously occupied the azimuth of your backsight line is 180º different from the azimuth when you were looking the other way from the backsight point to the point you currently occupy.

Remember that the azimuth of any foresight or side shot line is the backsight azimuth plus the angle right (remember to always turn your angles to the right - even if an angle to the left would be shorter).

Tools to Use

The spreadsheet below will calculate the coordinates of your instrument stations and side shots based on data you should have collected during your survey.

Traverse Calculator.xls