Designing shading devices by eye means simply lining up the shadows from obstructions with certain points in your model - based on the position of the Sun at different times of the year. There are a number of ways you can do this, each detailed in the following sections.
1. Lining up Shadows
The most obvious way is to display the effects of a shadow on a particular surface and then interactively manipulate the shading device until the right shadow length is reached.
2. Examining Sun Penetration
In a similar manner, if the aim is to prevent the direct Sun from penetrating into a space, you can also shape a shade by watching for Sun patches on the surface inside the window.
3. Viewing from the Sun's Position
By the time the Sun's rays reach the Earth, they are almost completely parallel. Thus, if we view the model in an orthographic projection from exactly the same direction as the Sun, then the objects and surfaces we can see will be exactly those exposed to direct Sun at that time. Within such a view, if we choose the right dates and times, we can manipulate the model an simply line things up accurately by eye.
4. Spraying Solar Rays
Taking the idea of solar rays one step further, ECOTECT allows you to visualise the actual solar rays from the Sun within the model. You can then track them as they bounce off surfaces such as a lightshelf and into the room. This way you can size and angle your lightshelf as accurately as you wish.