SMU CSI Camp: Phone GPS Location


You will use trilateration to find the location of objects, just like how cell phone towers find your phone's position. Learn more about finding a location by reading Phones and GPS Location.




Demonstrate how to use a compass to draw circles with a given center and radius.

The worksheet bellow gives problems using 2 or 3 ranges, for problems such as locating a cell phone or sketching a crime scene. You will have to scale distances on paper, e.g., 1 inch = 1 mile.


Use a compass, ruler, and range information to solve the following:

1. Julie is driving on the highway and calls to say she has a flat tire. She's not sure where she is, but sees a sign that says Smalltown is 2 miles away. We're still not sure where Julie is. Mark 2 possible locations.

(3/4 in = 1 mi)


Fortunately, Julie notices another sign for a McDonalds in 4½ miles, in Springfield. Put a check by Julie's location.

2. A cell phone is 2 km from tower A, 3 km from tower B, and 1.75 km from tower C. Find the location using a compass and mark the spot. Where is the cell phone? _________________________________
(Hint: Scale is 2 cm for 1 km. Measure from the tip of the balloon.)








3. Use a compass to sketch a crime scene, given the 2 distances in the chart. dNW is the distance to the Northwest corner, so put the tip of the compass in the NW corner. dSE is the distance to the Southeast corner, etc. Label items on the sketch by Item # or draw a picture! Drawing scale is ½ in. = 1 ft.

 Item #  Description  Distance 1 (ft)  Distance 2 (ft) 
 1  Body  dSW = 7'  dSW = 5'
 2  Bloody Footprint  dNE = 7 1/2'  dSE = 7'
 3  Bullet  dSW = 5'  dSE = 6'
 4  Gun  dNW = 9'  dNE = 3'
 5  Can with Fingerprints   dNW = 5'  dSW = 8'
 6  Handwritten Note Signed "Mark"   dNW = 7'  dNE = 4'



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