England-2011-lab1-orange

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Lab Write-up for the Orange Group (Charlie)

Overview

Greenwich, England is home to the Prime Meridian, the arbitrary line that signifies 0 degree longitude for global navigation. The lab assignment, Where am I?, asks us to determine where a particular location in Greenwich is located using different tools/methods to determine the latitude, longitude, elevation and distance to the Prime Meridian of that location.

Data Collection

The spot I was assigned was just outside the Starbucks in Greenwich:

View of the store at 54-56 Greenwich Church St

The lab instructions specify that we should use three different tools/methods to determine the latitude, longitude and elevation. Listed below are the choices I made:

Next the instructions ask us to determine what is due North and due South of that location:

Lastly the instructions ask us to determine the distance from that spot to the Prime Meridian using two different tools/methods, I used Google Earth and estimation for this quantity.

Equipment and Procedures

  1. Garmin etrex handheld consumer GPS unit, software version 3.5.0
    • Using the GPS involves powering it on, waiting for it to acquire enough satellite signals, noting the margin of error, and then switching the mode to waypoint which displays the latitude, longitude, and elevation. To obtain three readings I slowly spun in a full circle while chanting "umm" and then stopped and waited for the GPS to produce a new reading.
  2. Google Earth software, version 6.0.1.2032 (beta), running under OSX 10.6.6
    • Once Google Earth is launched you can enter the location of interest in the search box and then zoom-in to the appropriate magnification for the task at hand. To obtain three readings I moved the mouse around on the screen and then returned it to the point of interest and re-read the latitude, longitude and elevation from the status bar on the bottom of the screen.
  3. Estimation using a 48 year old white male American with a background in science and engineering
    • For the latitude I used the lamp post across the street and noted the latitude marked on it.
    • For the longitude I used the lamp post across the street and noted the longitude marked on it.
    • For the elevation I used the lamp post across the street and noted the elevation marked on it.
    • For the distance to the Prime Meridian I calculated my pace by walking the length of the Cutty Sark 3 times, averaging the number of paces, and then dividing the known LOA of 280' [1] by that value. Using this method my pace was determined to be 2.5'. Using the hand-held compass as a guide I walked a line due East from the spot to the Prime Meridian keeping track of the number of paces. I then reversed my direction and walked back to the spot following the same path. I averaged the number of paces from the two trips and then multiplied that value by 2.5' to obtain an estimate of the distance.
  4. Silva bog standard hand-held compass, circa 1975
    • While holding the compass on the outstretched palm of your hand, and using the centering bubble to ensure that it's level, a reasonably accurate reading can be taken if you hold your head directly above the compass and look straight down.

Measurements for each dimension were determined by averaging the three readings together.

Sources of Error

There are many sources of error, built-in and human, when using navigation instruments such as those employed for this lab. Below is a discussion of those as they apply to each instrument.

Results

Dimension Instrument Measurement
Latitude GPS xx.xx +/- 3m
Google Earth xx.xx +/- 3m
Estimation xx.xx +/- 3m
Longitude GPS xx.xx +/- 3m
Google Earth xx.xx +/- 3m
Estimation xx.xx +/- 3m
Elevation GPS xx.xx +/- 3m
Google Earth xx.xx +/- 3m
Estimation xx.xx +/- 3m

Directly North of the location is the intersection of two roads.

Directly South of the location is something really interesting.

The distance to the Prime Meridian as determined by Google Earth is xx.xx +/- 10m, by estimation it is xx.xx +/- 20m.

Appendix A: Raw Data

Dimension Instrument Reading 1 Reading 2 Reading 3
Latitude GPS xx.xx xx.xx xx.xx
Google Earth xx.xx xx.xx xx.xx
Estimation xx.xx xx.xx xx.xx
Longitude GPS xx.xx xx.xx xx.xx
Google Earth xx.xx xx.xx xx.xx
Estimation xx.xx xx.xx xx.xx
Elevation GPS xx.xx xx.xx xx.xx
Google Earth xx.xx xx.xx xx.xx
Estimation xx.xx xx.xx xx.xx

 

Dimension Instrument Reading 1 Reading 2 Reading 3
Distance to Prime Meridian Google Earth xx.xx xx.xx xx.xx
Estimation xx.xx xx.xx xx.xx

References

  1. Cutty Sark
  2. Prime Meridian
  3. Google Earth - Resolution and Accuracy
  4. Magnetic Declination Explanation
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