Geodesy Projections

Question 1

What type of measurements are longitude and latitude?

Answer 1

Horizontal

Question 2

What type of measurements are geoids?

Answer 2

Vertical

Perpendicular to gravity fields

Question 3

Why are 2D maps never fully accurate?

Answer 3

Placing a 3D object onto a 2D surface

Distortion occurs

Question 4

What is a Cartesian grid?

Answer 4

Eastings- longitude lines

Northings - latitude lines

Question 5

What type of map projections are there?

Answer 5

Cylindrical
Conical
Planar / azimuthal

Question 6

What do conformal maps do?

Answer 6

Preserve local shape and angles

Question 7

What do equal area maps do?

Answer 7

Preserve areas of displayed features

Question 8

What do equidistant maps do?

Answer 8

Preserve distances between certain points

Question 9

Conformal projections?

Answer 9

Graticule lines intersect at 90° angles
At any point on the map the scale is the same in all directions
Commonly used for navigation or meteorology

Question 10

Equal area projections?

Answer 10

All mapped areas have the same proportional relationship to the areas on earth they represent

Used for reference and educational graphs

Question 11

Equal distance projections?

Answer 11

Cake constant in all directions

Used for radio, seismic mapping and navigation

Question 12

What projections do the UK use?

Answer 12

Transverse Mercator projections

Ordnance survey national grid
Universal transverse Mercator

Question 13

What is the Transverse Mercator Projection?

Answer 13

Cylindrical map projection - conformal so distance is distorted

The further away from the meridian the more distortion

Scale factor = 1

Question 14

How do you calculate scale factor?

Answer 14

F = 1 + e^2/2R^2

e - distance as a difference of eastings
R - radius of ellipsoid at the point

Question 15

What is the scale factor between sub parallels?

Answer 15

0.9996

Question 16

What is the universal transverse Mercator?

Answer 16

Low distortion projection 
60 zones
Constant longitude
Each zone = 6° of longitude 
Zone one is at 177° W

Question 17

Curvature of Geodesics?

Answer 17

A line on the projection must contain the same intermediate points as that on the ellipsoid

The angle between the tangent to any two lines on the ellipsoid should have a corresponding angle on the projection

Question 18

What is OSGB36?

Answer 18

The triangulation of GB
1783-1853

Retriangulation
Concrete pillars placed on hilltops
1935-1962

100 to now 6000 points
Used to create the ordnance survey national grid
Uses the Airy 1830 ellipsoid
Central meridian 2°W

Question 19

What is the Ordnance datum Newlyn?

Answer 19

Geoid model - mean sea level as reference

Corresponds to the average sea level measured by the tide gauge in Newlyn 1915-1921

Question 20

What is the WGS84?

Answer 20

Used for GNSS positioning
Designed for positioning anywhere on earth with the origin being the centre of earth

Established from 1600 points

Designed to best fit the global Geoid
Most widely used
Correct and valid New Year’s Eve 1993

Question 21

What is ETRS89?

Answer 21

Earth centred earth fixed
Eurasian plate is static
Uk national coordinate system for 3D GNSS positioning
Monitored by 250 GNSS tracking systems

Question 22

What are the ellipsoids relative to the UK?

Answer 22

Airy 1830
International 1924
GRS80

Question 23

What are the projections relative to the Uk?

Answer 23

National grid
Irish national grid
UTM zones 29,30 and 31