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The Making of "Four Seasons in One Day"

Positioning the sun

There were a couple of options available to me for positioning the sun.  Terranim provides an option for animating the sun but this is not practical as it only provides a straight line between two points.  If the sun position is not defined in the TGS script then Terragen reads it from the TGW file. Since I was using Terratweak to create a TGW file for every frame, it would be relatively easy to simulate the path of the sun with a number of key frames.

Rather than produce a 100% accurate sun path I decided (for simplicity's sake) to use a simple inverted V-shaped path. 

Lighting Control

With atmospheric effects having a greater impact on the amount of light "reaching" the terrain I also had to consider keyframes for lighting and atmospheric settings based on the sun's altitude above the horizon. I experimented with adjusting exposure via the TGS script but this was too limiting in it's effectiveness. Apart from some minor tweaking of atmospheric settings, the main adjustments needed to be made to sunlight strength and glow amount, which could only be done via the TGW file.

There is a bit of "jumping" of lighting in the animation which may be due to a problem in TerraTweak but my main suspicion is with the range of values I used. I suspect that I should have included a key frame at a sun altitude of 8°

Clouds

While not technically impacting on the lighting I probably didn't do enough with clouds to warrant a separate page.  The first time I animated clouds I was disappointed with their appearance. While it was great that they moved across the sky, the fact that they did not change shape at all was too obvious and destroyed the illusion.  Throughout this animation, changes to cloud density contrast and density shift provided some interesting effects although the main changes were done over very short periods... so pay attention!  ;-) 

It would be great to be able to vary the random seed used to generate the cloud pattern so that clouds could change shape completely as they moved across the sky.

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This page, its contents and style, are the responsibility of the author and do not represent the views, policies or opinions of The University of Melbourne. All photographs © Ben Kreunen 2000

Ben Kreunen <bernardk@unimelb.edu.au>
Department of Pathology
Last modified: 13-Aug-2003