History of Positioning Flashcards
a position can be determined in two different ways
- **Relative: **to other landmark or features
*** Absolute: **coordinates of a point in space
positioning in the pre-space era
- historically,the most important pratical application of positioning was to provide safe ocean navigation
Tringulation
historically triangulation, the mesurments of angles
Based on the trigonometric rule that if one side and two angles of a triangle are known, the remaining sides can be computed
Measuring Angles: Theodolites
- surveying instrument of high precision
- measures both vertical and horizontal angles
through the use of trangalation **Geodetic Network **was created
- the geodetic points are historical basis for the mapping of the earth’s surfaces
- it provides a number of fixed stations whose relative and absolute positions are accuratly established
- these points can then be used to calculate other points by using triangulation
the geodetic points
- are medal stucked in the ground
- if maddled with it could lead people to jail
relative positioning
Ocean Navigation
- Navigation on the ocean was very probemetic
Pilotage
- first method of navigation used
- **before the 15th century or in costal navigation,with sight of land
** - based on visual triangulation to known landmarks
- no need for accurate position ,but that one is in a safe position or on a safe line
- generally helped by maps or nautical charts
**Dead Reckoning **
- first method of navigation on the open sea
- used from 15th to 17th century
- calculates position by using previously determined position,and advancing that position based upon estimated speed on time
- fairly accurate at short distances
- requires very precise information on speed and direction over** long distances** > which could cause a lot of erros
relative positioning
Celestial Navigation
- Dead reckoning errors accumalete over time
- so navigators sought other reference points on the sea
* most found that :part of the solution was in the sky and the other part relied upon time
for long distance travels also absolute positioning
Calculating Latitude:changes in the sky
The night sky changes for most of us
on a daily and seasonal scale
* The daily rotation of the Earth causes
stars to sweep through the sky
* The seasonal revolution of the Earth
around the sun changes our
perspective
Estimating Latitude:north star as a reference point
- To measure latitude we can point to:
- **North star **in northern hemisphere
- The North Star is nearly directly above the north pole
- No matter what time of year or day, the North star is always directly above the north pole
- The angle to the North Star directly
measures your latitude
absolute positioning
Longitude challenges
- Longitude was much harder
- And resulted in many ship wreaks
- For decades no one was able to come up with a practical solution to the problem
- Some searched for the solution in the skies, others in building a precise clock..
The Longitude Challenge/Answer
- The key to calculating longitude is time
- The distance from a line of longitude to the prime meridian can be measured in hours and minutes
- The Earth revolves once on its axis every 24 hours at the equivalent of 1° of longitude in four minutes, or 15° an hour
- The comparison of time between a known place (e.g. Greenwich) and the local time would determine longitude
absolute positioning
The Marine Chronometer
- John Harrison came up with
his H4 chronometer design in 1761 - Requires that an observer knows exact Greenwich Mean Time (GMT) at themoment of observation
- Every four seconds of time error, the
position measurement will be off by
approximately one nautical mile
——————————- - an very currate clock, that portrais no matter what the local time is, the time of Greenwich
- local time was measured by the use of the sun9if not previosly known)
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