MapPad has been designed to provided accurate measurements based on GPS location or map interaction. To get satisfactory results following methods have been used for length and area calculation.
1. Vincenty formula for distance between two Latitude/Longitude points
Please follow this URL to get the detailed description of the method used.
2. Lambert azimuthal equal-area projection to calculate the polygons area
Please follow this URL to get the detailed description of the projection.
To calculate area the Lon, Lat coordinates are being projected on the fly to the Lambert projection, the origin (centre of the sphere) is being set up on the beginning of each measurement to X,Y of the first registered point.
This method has been used to convert coordinates from Lon, Lat to Lambert X,Y
3. Conversion of WGS84 to British National Grid
The method used has been described in my blog – you can read it here.
For the datum conversion Helmert transformation has been used and it was described very well by Chris Veness in article Convert co-ordinates between WGS84 and OSGB36