Lab #3

Using GPS

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

This is relatively short lab utilizing a recreational grade GPS unit.  You will turn the unit on and get the coordinates of a point of your choosing (nearby).  You will then set the GPS unit to lead you to a permanent survey marker.  When you find the survey marker you will make a sketch showing what is on the marker.

What You Will Need

(Things Provided by the Department and Instructor)

1- A Garmin eTrex Legend handheld GPS unit.

(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

What You Will Do - Detailed Instructions

The class will be broken into two groups.  The first will go and find the survey point while the second group is instructed on GPS and Plane Survey Coordinate Systems.  When the first group returns the second group will take the GPS unit and go find the survey point, while the first group is instructed on GPS and Plane Survey Coordinate Systems.

(Lab Instructions - Part 1)

Take the GPS unit to an open spot away from buildings and trees.  On the right side of the unit, the second button from the top is the power button.  Push the button to turn the GPS unit on.  The unit will display an introductory screen and then go the Satellite Page.  This page displays a circle with little blips representing the location of satellites in the sky.  The closer to the center of the circle the blip is the more overhead the satellite is.  The closer to the outer edge of the circle the closer the satellite is to the horizon.  A text display just above the circle indicates the status of the unit.  Initially it will tell you to wait while it acquires satellite signals.  A little bar graph below the circle represents satellite signals the unit has tuned in to.  As the signal is locked in a black bar appears for that satellite signal.  When three for 4 signals have been locked in the text on the screen will say "Read to Navigate" and give you its accuracy.  The initial accuracy will probably be something around 100 feet.  If you wait a few more minutes the unit will acquire more signals and bring the accuracy down into the 10 to 25 ft range.

When the unit is ready to go, walk to the a near by point of interest.  At the bottom of the screen the unit will display position coordinates.  The will be N  XXº YY' ZZ.ZZ" W AAº BB' CC.CC".  The unit will also estimate your elevation (although be prepared for that elevation to be 50 ft wrong).  Write down the point that you went to (ie what building or parking lot or sign did you go to) and then write down the coordinates.  (Although your GPS unit has limited accuracy, commercial surveying GPS units can measure positions within a few millimeters.  A growing way of surveying if for the surveyor to mount a GPS unit on a pole and go stick the pole in the ground to get the coordinates of any point of interest.  Commercial grade GPS units will store and plot these points on a map for you.  What you have done is representative of how the most recent survey equipment can locate a point).

(Lab Instructions - Part 2)

Next you will have the GPS unit help you find a National Geodetic Survey Bench Mark.  The top button on the right side of your GPS is the screen button.  Pushing the button several times will page you through the screens to the Main Menu.  The Main menu has 6 little icon symbols on it.  The second over on top says "Find".

The button on the front of your GPS unit is a "joy stick".  Push it to the right to highlight "Find".  Then push the joy stick in to select Find.  The unit will display a menu asking you what you want to find.  Select "waypoint".  The unit will ask you whether you want to find the nearest or by name.  Select "by Name".  The unit displays a list of named waypoints.  Select Survey Point.  The screen will change to a description of the waypoint.  At the bottom of the page will be a menu saying "Goto" "Map" and "OK".  Select Goto.  The screen changes to the Navigation Page.

The Navigation Page displays a Bearing circle at the middle with an arrow pointed in some direction.  The arrow points the direction to the waypoint from your present position.  A display at the top tells you how far you are from the point.  Displays at the bottom tell you how fast you are moving and in what direction.  Of course in the real world you may not be able to blindly follow the little arrow.  If the arrow points to a lake it may be well telling you that the point is on the other side of the lake rather than suggesting that you should go jump in the lake.  Move in a practical and safe manner as guided by the arrow.

Eventually the unit will indicate that you are arriving at the point.  You are looking for a Geodetic Survey Marker.  This marker is a brass circle mounted inside a circular stub of concrete a little over a foot tall.  Not all survey markers are in this form although the brass circle in some sort of concrete base is popular for more recent permanent monument.  When you "arrive" according to the GPS unit, begin looking around for the monument.  When you find it, make a sketch showing what is on the brass circle.  The sketch should show all or most of the text including where it is located on the brass circle.  When you are finished, turn the GPS unit off by holding the on button down for several seconds.  Return to class to turn in the GPS unit.  (High precision GPS equipment is expensive and cannot be used at times or made accurate enough to use in all cases.  Despite this limitation of GPS, many surveyors now use GPS units to help them locate permanent reference survey points to work from in doing traditional surveys.  This exercise is representative of one use of low accuracy GPS by surveyors. - This is also being used by hobbyists who post coordinates to "treasures" on the internet for people to go out and find - this hobby is called Geocaching).

Comments on This Lab

GPS is the most significant new development in surveying in hundreds of years.  Visual lines of sight through telescopes between survey crew members are being replaced with radio signal lines of sight to satellites.  The types of motions illustrated in this lab are examples of things surveyors are using GPS for.  The unit you are using is not survey accurate however the difference between finding a point with a handheld recreational GPS and an RTK commercial grade GPS is a question of accuracy and software only.  Because software, antennas and microchips are changing rapidly the exact procedures and readouts one gets from GPS units is varied and not as standardized as with the regular machines and equipment of conventional surveying.  If you become involved in GPS surveying work you will have to spend significant time familiarizing yourself with screens, software and unit operations procedures.

Taking Field Notes

This lab is not suggesting a specific form of notes.  You must list your crew, the time and location of your survey, the lab #, as with previous labs.  You must indicate the point of interest that you found and its coordinates as reported by the GPS unit.  In finishing this lab you should convert these coordinates to the State Plane coordinate system as will be explained in the next section.  For the second part of the lab you will have a sketch showing what is on the brass survey point left by the National Geodetic Survey.

Finishing the Lab

Your GPS unit and almost all GPS units report coordinates in latitude and longitude, which is an excellent system for locating points on a sphere.  Unfortunately, conventional and local surveying work is done as plane surveys as if the earth locally in an area could be represented by a planer surface.  Indeed trigonometry and geometry on a spherical or ellipsoid surface is different and far for complex than Euclidian Geometry and planer trigonometry.  One problem then with GPS survey work is that it has an almost inherent disconnect with the planer surveys on which many traditional maps and property descriptions are based.  It is possible to convert GPS coordinates to planer coordinates.  The second part of this lab is a discussion and demonstration of software that can make these needed conversions.

To finish your lab assignment, transform the latitude and longitude coordinates for the point you located to State Plane coordinates for the Illinois west area (which Jackson County is in).  You will do this by entering the coordinates of your point into coordinate transform software in the computer lab.  The program will immediately give you the equivalent State Plane Coordinates.  Write down these equivalent State Plane coordinates on your notes next to the Latitude and Longitude of the point you selected and described and turn in your lab notes.