Again, in the glaciation and canyonism comparisons, the control picture on the left shows all settings at zero.

The effect of glaciation is to widen the base of valleys and so decrease the number of hills and mountains in a scene. At the same time, the mountains become steeper, with pointed peaks, and this effect becomes very exaggerated at the higher settings. Increasing glaciation settings can be useful in scenes containing water, because it gives larger low-lying areas where water is created. When the low-lying parts of the scene are not water, the valley floors are very rocky and uneven, and the rocks too have the exaggerated pointed shape.

Normally you would balance the effects of glaciation by raising realism to smooth out the low lying and flat areas of the landscape, but in all the examples below I have set all settings at 0 except the one being studied. The results at higher settings are very exaggerated, but they show you the nature of the the option.

 all settings 0 glaciation default glaciation 60 glaciation 100

Canyonism has the opposite effect from glaciation. Valleys are narrowed, and the sides of mountains made almost vertical, with flat tops. The effect is very like scenery such as the Grand Canyon in Arizona. Although the low lying areas are reduced by canyonism, effective water scenes can be created because the results are rather like fjords - narrow strips of water between high, steep mountains.

 all settings 0 canyonism default canyonism 60 canyonism 100

All of the examples of the four settings, on this and the previous page, are giving exaggerated impressions of their effects because I have used them in isolation. Normally you would start from their joint default positions, and raise and lower one or more a little to get the effect you want - perhaps raising glaciation a point to widen valleys or get more sea area, or lowering smoothing a point because you want a more rocky landscape, or lowering realism to give more rocky flat areas. It would be very unusual, and give an artificial looking scene, to take one or more of them out altogether.


We turn now to the group of commands accessed by the Modify Terrain button. These are all applied after the terrain has been generated, so I am now able to generate one terrain at the default settings, to which these modifications can be applied one by one, so that you get an idea of their effect. It will be the control scene in each group of examples. After each modification I reloaded the control terrain and world file, so that direction and lighting remained the same for the next one.

I am going to begin by studying the effects of glaciation and canyonism when applied as modifications after the scene is generated, rather than when it is generated which we have been considering hitherto. We no longer have any control over the degree of each applied, but they can each be applied more than once and they can be applied singly or in combination.

Glaciation still widens the valleys and makes the mountains more isolated, but there is not the same degree of exaggerated point in the mountain shape, and the valley floor is no longer rocky. This is a more natural version of the effect.

Canyonism still narrows the valleys and steepens the mountains, but again the effects are more natural that those achieved when increasing canyonism in the generator. The mountains are not quite so vertical and their tops not so flat.

If both canyonism and glaciation are used on the same terrain, the qualities of both are subtly combined. If you look closely at the examples below you can see that in the last picture, the general shape of the mountains is that given by canyonism, but the space between them conforms to that given by glaciation. The mountain on the left is halfway, in height, between the height it became in the two separate modifications. It is about the height it was in the original terrain, but is now much steeper. The valley area in the foreground is smooth, as it is in the glaciation example - smoother than in the original.
control scene glaciation canyonization glaciate and canyonize

Bound Vertical allows you to specify a range between which the heights of objects in your terrain must lie. After setting the levels, when you click the bound vertical button, the lowest points in your terrain will be set to the lowest in your bound vertical settings, the highest points to the height you give as your maximum, and everything in between scaled accordingly. The control scene and viewpoint is still the one used for the last set of examples, but I have not repeated it here so that I can give four different bound vertical settings. Again, I have reloaded the original terrain for each example.

In the first picture, you see the result of tightening the bounds so that the range of heights is very small. With the default settings in the second one, a wider range is given, and the mountains appear higher and we are aware of a hollow in the foreground.

You would expect the settings in the third picture to give lower mountains, but the lowering of the lowest levels has increased the hollow in the foreground, and the camera is now in it. It has to be tipped back to view the target position and the mountains look higher than they are because of this. We shall be studying camera position and height later in the tutorial, but I included this here so that you can see that the apparent height of the mountains is affected by other things than the height you have specified in bound vertical.

In the last picture of the series I have raised the lower setting to 0 and the upper to 70. Although at first glance you would expect the mountains to appear much higher in this picture, the overall difference between the lowest point and the highest is only a little more than the default setting and is, in fact, less than in the previous one. The camera is no longer below the level of the rim of the hollow. The combination of these factors gives us a scene which has only changed a little from its predecessors. You can see from this series of pictures that what actually governs the apparent height of the mountains when you use bound vertical is not the maximum height you set, but the difference between the lowest point and the highest.

-5 to 5
-32 to 32 (default)
-60 to 15
0 to 70
-5 +5 -32 +32 -60 +15 0 to 70

The Scale Vertical command gives you a choice of settings, stretch or squash. The operation is straightforward, simply stretching or reducing the overall height of the terrain to the percentage of the original that you specify. The changes in the height of the scenery are much more predictable than with bound vertical, because with stretch vertical the proportions remain the same. Again, I am using the same control picture and have reset the terrain before each change. Stretch percentages are all over 100%, squash all below 100%. Setting either option to 100% makes no change to the terrain.

In both of these options, the method of use is first to click on stretch or squash, then to type in the percentage you require, and finally to start the operation by clicking on the scale vertical button. But to be honest, I am not quite sure why the two subdivisions of scale vertical exist. If you click stretch and enter 50% you will get the same result as if you entered the figure in squash, and similarly, if you click squash and enter 400% you will get the same result as stretch 400%.

I suspect that they are only there to enter a suitable default starting percentage for the two options. You can, in fact, ignore the stretch/squash buttons, type the percentage that you wish to use straight into the box, hit scale vertical, and the adjustment to the terrain will be made. You need only remember that a percentage below 100% will lower the height of the mountains, one above 100% will raise it.

control stretch 150% stretch 200% stretch 400%
control squash 75% squash 50% squash 25%

The last terrain modification, clear/flatten, removes all objects from the terrain leaving a completely flat surface. The most likely reason for wishing to do that, since you can set the generator to clear the previous terrain before generating another, is to allow you to paint your own terrain, using the paint brushes, or sculpting tools. Use of these tools was covered in page 1 of the tutorial. There I discussed using them to modify quite small areas, but they can also be used to paint an entire landscape, and you can use the modification options on a terrain you have painted yourself.

On the next page we shall conclude the exploration of the terrain generator settings with a study of the methods of combining terrains.