9.1. 3D Sky Maps¶

9.1.1. What’s a 3D Sky Map ?¶

Let’s imagine for starters that we’re at a point on a completely flat surface, without anything blocking our view. Our result would be something like this :

Of course in an urban setting, some of our rays would be blocked, and the associated dome faces would not appear :

9.1.3. What Can I Use Them For?¶

On their own and at a first glance, theses domes help you assess the openness of an area, the local skyline and roughly estimate the sky view factor. But they hold much more interesting information when used, for example, to assess solar radiation. As we’ve seen, we have methods to calculate the Sun View Factor after having drawn Sun
Paths.
What happens when we reproduce this procedure on our 3D Sky Maps ? To try this out, first create your domes, then click t4su > Edit > AutomaticReverseFaces because half of your dome’s faces are facing inwards. Then proceed to draw your Sun Paths and calculate your Sun View Factor over the layer containing your 3D Sky Maps. Finally, use ColorFaces to depict the differences in energy received by each face :

See also

Sun View Factors

Drawing Sun Paths

3D Sky Maps Created by Point-And-Click, Colored by Direct Solar Irradiation Value

We can see a lot more information at particular points in space than when doing a regular `SunViewFactor over a tesselated area:

We can see what parts of the sky contribute most (and least) to our direct solar irradiation. Naturally, North-facing faces receive the least sunlight, and Southern faces at a roughly 45° vertical angle receive the most. We can thus find which sections of the sky contribute most to the points’ solar energy gains.

9.2. 3D Sky Maps and Building Facades¶

3D Sky Maps and Building Facades both start from a half-dome, at the center of which is the point of interest. Rays start from the center point, pass through the center of each dome face and continue on, either hitting a facade or not.

Whilst Building Facades will only show the dome faces who’s rays have hit an obstacle, 3D Sky Maps will only show those that have not : They show complementary information. So when is one or the other more appropriate?

Sky maps are much more useful in showing which parts of the sky are visible at a certain point. They hold an advantage over 2D Sky Maps,in that the sky is not projected over a 2D surface: they are not deformed by any necessary spherical projection.

The BuildingFacade module works great for street-level visibility : it highlights the skyline, the openings in the urban space represented by “dips” in the dome formation, allowing you to assess the relative confinement of urban space.

Once built, the dome faces also hold an attribute, “dist_to_facade”(float). This feature expresses the distance between the point of interest and the obstacle represented by the dome face.

You can view it by clicking View > ColorFaces and choosing the dist_to_facade attribute.

Originally, the faces all turn inwards: the results may be more visible if the faces where reverted. This can be easily achieved by selecting Edit > AutomaticReverseFaces, and selecting your BuildingFacade layer. Sometimes, intersecting faces are not automatically reversed. For an optimal result, render your building layer invisible before reversing your BuildingFacade layer.

9.3. 2D Sky Maps and Vegetation Modelization¶

As we have seen, we can easily cover large areas by multiplying a single object, such as a person to make a crowd or a tree to make a forest. There are more than 1400 trees to choose fromin the 3D Warehouse, you really have a large choice. So are all SketchUp trees the same? What types are there and how do they affect the results of our visibility studies? Let’s take two concrete examples.

9.3.1. First Tree : the FaceMe Tree¶

If you’re familiar with Sketchup, you may know about the faceMe technique. Basically, a 2D Object is set to automatically turn to always face your camera, no matter which way you look at it (unless you look from above).

9.3.2. Second Tree : the Carboard Cutout¶

The Cardboard Cutout also uses the faceMe method for it’s vertical face, but also has an added horizontal face.

9.4. Sunny Sky Maps¶

We can project given sun paths onto our 2d sky map. This allows us to quickly understand buildings’ impact on solar availability at a point in space, over different periods of time.

First, create the sun paths you wish to have on your sky view graph.

In this example, we will be using the sun paths of Winter and Summer solstices, as well as an equinox, at a latitude of 47°. This allows us to see the range over an entire year.

Next, click on Extensions > Sun views > SunnySkyMap2D :

In the following command box, first select the layer containing your sun path:

• Enter the number of rays used for the calculation, ie: its precision in finding the contours of the surrounding buildings
• Set the visual range : this is the size of your graph. This depends your project and your personal preferences : the amount of space you have available to plot the graph, how far out you would like to zoom and still read it…
•  Select the height at which you would like to calculate your sky view factor (z0). If you would like to visualize projections at ground floor, 0.0 or 0.1 are an acceptable inputs.
• Select your unit of length. Be sure to always keep the same units throughout the entirety of the project!
• Next, select the type of projection you would like to use. If you’re not sure which one fits your needs best, check this page for more ample information.
• Finally, you can change the color of the building projections.

Once you hit OK, you can start clicking anywhere on your project to insert an graph at that location.

Reading such graphs are relatively simple. The disc represents a 360-view of the sky: the ground floor is projected at the circumference, whereas the center of the disk is the point in the sky directly above it (what happens in between depends on your type of projection). The filled-in parts of the graph represent parts of the sky that are blocked off by obstacles.

If a point of the Sun Path is contained in the filled in areas of the graph, it means that at that specific time and place the point you are studying is in the shade. Conversely, a sun path point that is not superimposed over a filled in area of the graph means there is direct sunlight at that specific time and place.