PAGE 15

HEAVENS ABOVE

Sky and clouds are present in Terragen when you open the program, so you can render a scene without making any changes to the sky. But if you want to take control of the sky appearance, you need to use the sky generator.

cloudscape buttonThe cloudscape button, the middle one in the row down the left side of the workspace, brings up the cloud generator.

The top control is the layer manager. At the time of writing, although it possible to add several layers of clouds, the renderer will only render one layer correctly, and trying to use two layers will leave you with a sky that resembles neither. When Terragen is completed, it will be possible to have several layers of clouds, at different heights, in the sky, and produce very authentic skyscapes. Even with only one layer, the skies produced are very realistic.

The default clouds are light white fluffy clouds. Clouds are saved in the World File, and when you open a World file, the cloudscape generated is the one you were looking at when you saved it. The skies have changed in the examples throughout this tutorial because many of the illustrations were made in version 6, before cloud saving was introduced.

Before considering the effects produced with the various controls on the cloud generator, I want to deal with the problem of a black gap between sky and land at the horizon. A frequent cause of this is the target position having a lower altitude than the camera position. The camera pitch is a minus value. Less sky is generated and what there is does not meet the land horizon. If there are mountains to cover the gap, all well and good, but if not, you get the effect shown below.

gap at horizon

gap closedAlthough, in theory, raising the pitch or the height above the terrain at the target position, ought to correct it, it frequently does not, because although the camera is tilted back so that more sky is visible, less land is visible too and the gap is still there. Moving the sight line, camera and/or target positions, will usually clear it, but that will give a different view on the scene and may not be what you want.

On the cloudscape generator panel, halfway down on the right, there is a setting for cover size, and the default is 4096. If you raise this figure the sky will cover a bigger area of the image, and cover the gap. But if you raise it too much, so that the sky covers too great an area, the program may close down with a run time error, so I usually raise it 1024 at a time, and keep testing the rendering, until the gap is closed.

A cover size of 8192 closed the gap on this image.

Clouds casting shadows on the landscape was introduced in version 8. In order to use the feature you must first check Clouds Cast Shadows in the lighting controller. The effect is more pronounced if the figure for metres covered by the terrain is raised. Just as in nature, if you can see a larger expanse of the landscape, you are more aware of the changing light and shade caused by the clouds than you are with a closer view over a small area. For the picture below, which shows this effect, the figure was raised to 38400.

ex285.jpg - 15kb

In the tables below, illustrating the effect of the various controls, the left hand image shows the clouds generated by the default setting of the control in question.

ALTITUDE = 100 (default) ALTITUDE = 50 ALTITUDE = 200
height =100 height=50 height=200
First, cloud altitude. Lowering the altitude of clouds gives bigger clouds, but may also result in larger expanses of blue sky. Raising the altitude makes smaller, more distant clouds, but because they are further away more are visible, and the the blue sky between them seems less.

DEPTH/THICKNESS = 8 (default) DEPTH/THICKNESS = 4 DEPTH/THICKNESS = 16
thickness=8 thickness=4 thickness=16
The effect of changing cloud depth and thickness is most easily seen in the examples above in the cloud at the very left edge of the picture.

high thinlow thickAltitude and depth and thickness are often used in combination. On the left is high thin cloud (altitude=250 depth and thickness=2) and on the right, low thick cloud. (altitude=50, depth and thickness=25)

On the next page I shall conclude the survey of the cloud generating controls, and the tutorial will end with a final rendering of the picture I have been building up throughout it, after applying the cloud generating controls to produce a suitable sky.

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