Specifying ellipsoid models

In this exercise we will introduce some of the many ways one can specify the ellipsoid model used in projections and transformations.

We will be using the Mercator projection to illustrate the different ellipsoid settings, but note that the same parameter settings can be used for setting the ellipsoid used for most PROJ projections and transformations.

Download the gie file for the exercise: ellipsoids.gie.

Exercise 1: Ellipsoid radius

Use a sphere of radius 1 as the ellipsoid model

Hint

Check the Mercator documentation to find out how to specify an ellipsoid

operation   +proj=merc  <your answer here>
tolerance   1 cm

accept      24.745          59.437          # Talinn
expect      0.4319          1.2975

Exercise 2. Specifying a ellipsoid

Set up a Mercator projection that uses the Hayford (International) ellipsoid

Hint

Check the Mercator documentation to find out how to specify an ellipsoid

Hint

Running proj -le will return a list of ellipsoids and their parameters.

operation   +proj=merc  <your answer here>
tolerance   1 cm

accept      24.745          59.437          # Talinn
expect      2754709.2020    8238786.4803

Exercise 3. Semimajor axis and inverse flattening

Specify the Hayford ellipsoid by its semimajor axis radius and inverse flattening

Hint

Find the parameters in the list returned by proj -le

operation   +proj=merc  <your answer here>
tolerance   1 cm

accept      24.745          59.437          # Talinn
expect      2754709.2020    8238786.4803

Exercise 4. Semimajor and semiminor ellipsoid axes

Set the Clarke 1866 ellipsoid by its semimajor and semiminor axis radii

operation   +proj=merc  <your answer here>
tolerance   1 cm

accept      24.745          59.437          # Talinn
expect      2754630.7723    8238298.4968