SUN-PATH DIAGRAM PROJECTION METHODS
Most of the real detail in a sun-path diagram is usually around the horizon. This is where adjacent buildings, trees and other site objects provide the greatest levels of obstruction. To increase detail at these low altitudes, different sun path projection methods can be used to essentially 'squeeze' altitude angles towards the zenith and expand them around the horizon. This applet demonstrates the most common altitude projection methods and shows how they can be mapped in both sky-dome and orthographic sun-path diagrams.
Description
The aim of this applet is simply to demonstrate how the different projections methods differ as they are mapped over sun-path diagrams. To do this, the diagram smoothly transitions between spherical and orthographic mapping as well as between spherical, linear and stereographic projections. Use the DIAGRAM button menu (F5) to switch between these settings.
Spherical projection involves simply mapping the altitude lines from the celestial sphere directly onto the ground for a sky-dome map or a surrounding cylinder for an orthographic map). Linear projection maps altitude lines linearly along the radius of a sky-dome map or the y-axis of an orthographic map. Stereographic projection is a little more complex, but you can read more details about it on Wikipedia .
Display Options
You can use the OPTIONS button menu (F4) to change the main display settings. This menu lets you toggle overlay panels that show solar information, the world map and simple instructions. You can also use it to change the size of the world map, overlay world time zones or select different views of the model.
Using the Display Options… menu item (Ctrl+F4), you can determine what components of the sun-path diagram are displayed and how they are shown. This allows you to tailor the image to suit your particular demonstration or application.
The only real way to understand the use of these applets is to experiment, so please feel free to simply play about with it.