Adding earth curvature and atmospheric refraction corrections

[timchurches]

Hi, first of all thanks for viewscape, we're a citizen science association and we've been using it to provide principled, evidence-based information about the view shed and visual amenity impacts of proposed wind farm developments in our local area, given that information provided by the developers and opposition groups tends to be less principled and potentially too optimistic or too pessimistic about impacts. We are in the Central Tablelands of News South Wales, Australia, about 200km west of Sydney. So far viewscape seems to be coping with quite large DEM rasters, around 22979 by 19397 cells of 5 metre resolution data and calculating the view shed with a radius of 35 or 40 km. We are doing this because the major town in the region is about 25 to 30 km away from the proposed wind farms. Due to the distances involved, we are very keen to incorporate both earth curvature correction and atmospheric refraction correction into the view shed analyses. Are there any plans to implement these in viewscape? If not, do you have any suggestions for how we should go about implementing them? We have good R coding skills and moderate C++ skills, but access to high-level C++ coding help if required. We've been researching the various models for curvature and refraction corrections, and one of the well-known approximations should suffice, such as described here: http://walter.bislins.ch/bloge/index.asp?page=Advanced+Earth+Curvature+Calculator

[timchurches]

Here is an example of the calculated viewshed for a single hypothetical turbine: https://oberon-citizen.science/demo_viewsheds.html . Looking at the viewshed raster in Leaflet in the second map on that page, against the topographic or hill-shaded base map, it seems to have very good face validity. There seem to be linear north-south artefacts in the view shed raster visible at high zoom levels, which may be due to issues in the elevation map eg missing values which should be filled by interpolation, but they aren't showstoppers. We also hope to encode the apparent size in the view shed raster, with as a colour gradient or an alpha channel gradient, as well as some of the other metrics views cape provides if we can assemble the required additional data.