############################################################################### 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. ############################################################################### 1. Use a sphere of radius 1 as the ellipsoid model: ------------------------------------------------------------------------------- Hints: * Check the Mercator documentation to find out how to specify an ellipsoid: https://proj.org/operations/projections/merc.html ------------------------------------------------------------------------------- operation +proj=merc tolerance 1 cm accept 24.745 59.437 # Talinn expect 0.4319 1.2975 ------------------------------------------------------------------------------- 2. Specify the Hayford (International) ellipsoid ------------------------------------------------------------------------------- Hints: * Check the Mercator documentation to find out how to specify an ellipsoid: https://proj.org/operations/projections/merc.html * Running `proj -le` will return a list of ellipsoids and their parameters. ------------------------------------------------------------------------------- operation +proj=merc tolerance 1 cm accept 24.745 59.437 # Talinn expect 2754709.2020 8238786.4803 ------------------------------------------------------------------------------- 3. Specify the Hayford ellipsoid by its semimajor axis radius and inverse flattening ------------------------------------------------------------------------------- Hints: * Find the parameters in the list returned by `proj -le` ------------------------------------------------------------------------------- operation +proj=merc tolerance 1 cm accept 24.745 59.437 # Talinn expect 2754709.2020 8238786.4803 ------------------------------------------------------------------------------- 4. Set the Clarke 1866 ellipsoid by its semimajor and semiminor axis radii ------------------------------------------------------------------------------- operation +proj=merc tolerance 1 cm accept 24.745 59.437 # Talinn expect 2754630.7723 8238298.4968 -------------------------------------------------------------------------------