APSalin, a company specializing in “Software development and data management for radio and television broadcast engineering”, offers a free set of handy online calculators and reference materials:
- Converters to/from geographic/geodetic – Mercator – UTM – Cartesian coordinates
- NAD27 to NAD 83 converter (latitude/longitude only)
- Latitude/longitude DMS to decimal & vice versa
- Great circle distance/bearing between two points
- Destination (enter position-bearing-distance, get coordinates of destination)
- Reference tables showing what distances on map represent for various map scales, and what various distances in real life correspond to on a map at a specific scale. Tables are given for both metric and imperial units; if you ever need an argument for doing everything in metric, this is a good place to start.
- Reference tables for DEM resolutions in arc-seconds converted to meters and feet
- Ellipsoid parameters for various datums