Études d'ensoleillement, diagrammes d'ombres (avec POV-Ray)

The following are very rough hints on how to proceed to obtain images useful to draw a shadow-casting diagram.

Project-preparation

When preparing your project, make sure you consider the following (this list is not intended to be a complete check-list).

Ensure your model is correctly georeferenced.
All buildings within a certain radius should be included. Significantly influent buildings need to be modelled with higher precision (think of roofs, balcons, etc).
In general, topography must be modelled in sufficient detail (e.g., think of the influence of a mountain).
Trees (esp. forests) might need to be included.

Camera definition (start in 3D-mode):

You can use the following to get a view from above with nearly no perspective effects (a nearly parallel projection):
1. Specify the camera coordinates:
  - camera_position: h=~2000–5000m
  - camera_lookAt: h=0, x:= camera_position.x + 1
2. use (zoom +) to get the wanted image size (press a few times; be sure you use the zoom button and not the one to get closer (nor the mouse-wheel)

To be able to reproduce the sun-study, keep the camera as a camera-element in the project (see tool in 3D-mode).

POV-Ray settings:

Model-content options:
- Show terrain: ground-surface color: white (for good contrast)
Light:
- sun-lighting level: ~10
- indirect and camera lighting levels: 0
Image:
- For efficiency, start using a low quality image ("draft" or less).
- For the final version of your images, you might want to increase quality (do so only once you're happy with all other settings)
Select "generate sun-study series" and specify
- wanted days of the year (and time interval for each wanted day),
- time-interval between instant-images,
- other options (in particular, the option to create an enhanced day-average image is very handy; see notes below)

Notes

There is an option (Create an encanced 'day-average' image in Realistische 3D-Darstellung (POV-Ray) > generate a sun-study series) that helps you to find the long-time-shadowed areas, by producing an additional day-average image in which areas that are shadowed above a certain number of instant-images are darkened.
To determine if a certain area is in shadows, the program compares each "normal" instant-image with a shadowless version of it, pixel by pixel: if a pixel in the normal instant-image is darker than in the shadowless image, it's considered to be in shadows.
Note (details): In the way the term "shadow" is used here, "not being directly illuminated by the sun" in an instant-image does not imply "being in shadows". For simplicity, let's consider a face of a very small and (infinitely) thin, planar wall (e.g., think of one that corresponds to a single pixel in an instant image). When it's not directly illuminated by the sun at a certain instant (dark in the corresponding instant-image), this can be
1. because there is anther surface blocking the rays coming from the sun (this other surface casts shadows on our wall-face), or
2. just because of its orientation (e.g., the sun is currently illuminating the other face of our wall).
In the second case, both the "normal" and the shadowless images will not differ: our face is not considered to be in shadows. Thus, when using the above-mentioned darkening option, such a face-part will never be darkened in the enhanced day-average image. Roughly speaking, this feature has the benefit of excluding regions that are not illuminated because of "themselves" (and not because of the presence of some object that might cast shadows on them, which is the focus in shadow-casting studies).

Concerning the time interval between instant-images, 30 min is often sufficient for simple cases. For complex cases (e.g. building(s) with distinct high "peaks"), you might often need to use a shorter interval.

You might sometimes want to use a raster element with plan information (see related options under 3d-model-content > Show DTM).

The use of textures (e.g. using grass instead of a plain color) increases the rendering time.

Example

The following are day-average images for a 30m-heigh cylindrical building (time-interval for instant-images: 30 min):

day-average image:
enhanced day-average image (base for a 2h-shadow diagram); see comments above:
2h-diagram (the red 2h-line was added "manually"):