Terragen allows two ways of combining terrains. The first one is in the Generate Terrain options. Under Action, on the terrain genesis dialogue box, you can opt not to clear the existing terrain, but to add the newly generated terrain objects to it.
When you select this option, glaciation and canyonism are not available, but realism and smoothing are. The picture on the left is our control picture, and the one on the right the result of adding a new terrain to it, at the default settings for realism and smoothing. It is rather bland and featureless.
In the picture left I have used glaciate and canyonize from the modify terrain menu, which has made it a little more interesting, and you could go on to use bound vertical and stretch vertical to improve it more. But this method of adding to a terrain gives minimal control over the terrain, and the scene we have now bears little resemblance to the one we started with.
However, we can have more control over blending new features into the scene by using the Combine With feature. Let us suppose that I want to put this improbable looking mountain on the right into our control scene. I made the terrain for this mountain myself, deliberately making it an unusual shape so that you will be able to see that it has been inserted, and also making it on an otherwise flat terrain so that nothing else is there to change our original terrain.
The Combine With option allows two different terrains to be merged. At the time of writing this option is not yet completed and the facility for opening or importing a secondary terrain has not yet been implemented. However, you can use it by first loading a terrain into the terrain generator, and then selecting Combine With followed by Copy Existing. This will load that terrain as the secondary terrain. You can then load another terrain into the generator and this can be combined with the one you have already stored as the secondary one.
These are the two terrains I am going to combine. The one on the left is the terrain for the control picture, and the on the right the one for the tall spiky hill.
The viewpoint line is shown in both. The camera position is at the top right end of the line, and the target bottom left. The hill, as you can see, is directly in front of the sight line, and as the sun is on a similar line, when it is in the control picture it will be almost silhouetted against the sun.
There are six combination methods, each one giving a different effect. There is also a small preview of the combined terrain. When you select a method and click the Modify Terrain button, the new combined terrain shown in the preview is transferred to the terrain generator. You can then close the combine with window and use this new terrain just like any other, applying modifications if you wish and generating pictures from it. In the series of examples below, I have not made any modifications to the combined terrain.
In the top row of each section of the table, the control picture is the one I used for the secondary terrain, and the mountain the terrain being combined with it. For each picture I have reloaded the mountain terrain before producing a new combination, and left the control terrain unmodified as the secondary terrain. The terrain shown with each render is a scaled down copy of the merged terrain from the terrain generator.
Since the results can be subtly different in some of the methods if the terrains are reversed, in the second row of each section the secondary terrain is the spiky mountain, and the terrain being merged with it is the control picture.
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In the next section of the tutorial we shall return to the snow and lake picture I have been building up during the previous sections, and study the control of camera angles and their effect on the viewpoint