BlomURBEX extended - adding detail
The Ordnance Survey base mapping will principally only have building outlines at ground level. In urban areas with complex multiple storey buildings this may need to be enhanced.
By using a combination of horizontal and bearing measurements, BlomURBEX can be used to build up a comprehensive building footprint and/or roof plan at various levels directly on to the Ordnance Survey base mapping.
Taking roof measurements using BlomURBEX vertical view:

Adding measurements to the base Ordnance Survey mapping:

>>Next step - BlomURBEX relative and absolute measurement