English Glossary

impedance

Angle measured from directly overhead to the geometric centre of the sun's disc, as described using a horizontal coordinate system. The solar elevation angle is the altitude of the sun, the angle between the horizon and the centre of the sun's disc. If θs is the solar zenith angle, then the solar elevation angle αs = 90° – θs.

Efficiency of a collector when there are no thermal losses

ZTV - Maps produced are theoretical because they estimate exposure of proposed development based upon landform data only, and take no account of intermittent screening by vegetation or structures. ZTV maps estimate visibility of the proposed development in the surrounding landscape and not its 'visual influence'.

ZVI - Provides a visual representation, usually presented as a map with markings or colourings, of the area over which a site and/or a proposed development may be visible.

zone of theoretical visibility

zone of visual influence