GNSS and Coordinate Systems

Question 1

What is a coordinate system?

Answer 1

A predefined reference with a unit to measure displacement.

Question 2

What is the actual shape of the Earth? (Undulated shape)

Answer 2

Geoid

Question 3

What is a Datum?
Give the steps to creating a datum. (3)

Answer 3

Orienting the suitable ellipsoid to fit to a focused area
1. Ellipsoid is scaled down
2. Moved linearly along x, y, z axises
3. Rotated along x, y, z axises

Question 4

What are the datums used for SL?
Give the coordinates for Piduruthalagala for each.

Answer 4

• Kandawala (200000, 200000)
• SLD-99 (500000, 500000)

Question 5

What is the best map projection for SL?

Answer 5

Transverse Mercator

Question 6

Define Global, Local and Projected Coordinate Systems

Answer 6

• Global - CS used for measurements all over the world.
• Local - CS used for measurements in specific areas in the world.
• Planar/Projected - converting 3D world to a 2D map

Question 7

Give an example each for global and local ellipsoids.

Answer 7

• Global - WGS84
• Local - Everest 1830