Galloper Wind Farm Project - National Infrastructure Planning

2842_LVIA
September 2011
GALLOPER WIND FARM SUBSTATION
Appendix 3. Methodology for Preparation of Visuals
ZTV Studies
17.1.39. ZTV studies are prepared using the ArcGIS Viewshed routines. This
creates a raster image that indicates the visibility (or not) of the points
modelled.
17.1.40. The visibility is modelled taking into account both the curvature of
the earth and light refraction, in accordance with Scottish Natural
Heritage guidance (Visual Representation of Windfarms Good
Practice Guide, SNH February 2007). Within a ZTV all observers are
presumed to be 2m tall (in order to compensate for the likely margin
of error within the ground model as indicated within the SNH
Guidelines). The ZTV also begins at 1m from the observation feature
(for example the development) and will work outwards in a grid of
the set resolution (generally 20-30 sq. m) until it reaches the end of
the terrain map for the project.
17.1.41. For all plan production LDA Design will produce a ZTV that has an
overlay of the 1:50,000 Ordnance Survey Raster mapping in a Bitmap
50% threshold form. The ZTV will be reproduced at either 1:50,000 or
1:100,000 scale depending on the study area. For a typical 25km radius
study area, the ZTVs will be printed on an A1 sheet at 1:100,000 scale.
Ground Model Accuracy
17.1.42. Depending on the project, different height datasets may be used.
Ordnance Survey Landform Profile (roughly linked to quality of 10K
mapping) and Landform Panorama (roughly linked to the quality of
50K mapping) are supplied as point datasets from which a
triangulated mesh is created within GIS (often referred to as a TIN).
Below is listed the different data products and their specifications: