I am returning now to the snow and sea picture I have been building up through many of the sections of this tutorial, in order to study the camera settings on the render control panel. We looked very briefly, in the first sections, at changing the camera height in order to make water visible. Now I want to look at the settings in detail, and their effect on the picture as a whole.
At the top right of the render panel are co-ordinates for the camera position and the target position. For both there is the east-west co-ordinate (x), the north-south co-ordinate (y) the altitude above sea level (z) and the height of the camera above the terrain, which may be fixed or not as you wish.
The x and y co-ordinates behave as though the terrain map is facing due north. Altering x will take the position being changed left or right of the current position, and altering y will move it up or down the terrain map. To move it diagonally you must change both co-ordinates.
x co-ordinate 0 is on the left side of the terrain, and x co-ordinate 256 on the right. You can use minus numbers, or numbers above 256, but the effect is the same as changing the y co-ordinate, and the position moves up the side edge of the terrain.
y co-ordinate 0 is at the bottom of the terrain, and y co-ordinate 256 at the top. Again, higher or minus numbers will move the position in the x axis along the top or bottom edge.
For both of these co-ordinates I would advise always using values between 0 and 256 which give you control over the position. Figures outside this range are less predictable, and confine you to the edges of the terrain anyway.
The z co-ordinate is the height of the camera lens above sea level. It works in conjunction with the height above the terrain. Our camera is on a tripod, and is not fixed at ground level. If you check the fixed height above the terrain box, you are free to alter the tripod height. You will see the altitude changing, as your camera height is added to the position's height above sea level on the terrain. You can set a particular camera height, uncheck the box, and fix the tripod height, so that wherever the camera is placed, its lens will be at the stipulated height above ground level. The program will calculate the height above sea level automatically. If there is a large obstruction like an upward slope in the foreground, raising the height above the terrain can allow the camera to see over it. If there is no foreground at eye level, and the scenery which comes to the bottom edge of the picture is far below, the picture can feel unsatisfactory. Lowering the camera height above the terrain may allow a foreground feature to protrude a little into the scene.
It is possible for the camera to be below sea level, if it is placed in a valley bottom or a hollow. If water is not involved in the scene, this will simply alter the perspective. But if you have water in a scene, and the camera altitude drops below the water level you set in the water control panel, the water will not be rendered and you will have a black area in the scene. So when placing the camera for a water scene, you should change the camera altitude if the value falls below your water level.
The co-ordinates work in exactly the same way for the target position. The z co-ordinate and fixed height value mean that you do not have to focus the camera on the ground at your chosen point. You can focus at ground level, treetop height or even below ground level if you wish.
The z co-ordinates of both positions also affect the camera orientation values, but we will examine those in more detail in a moment. First I want to give you some examples of the changes to the scene made by moving first the camera, and then the target positions, in the x and y directions. Where the change would make water invisible, I shall also change the z co-ordinate to restore it.
In the table below I show the effect on our picture of moving the x and y co-ordinates of the camera position. They have a considerable effect on the scene. Not only are the views of the mountains changed, but because the position of the sun changes, or goes behind the mountains, the appearance of the water changes too.
|x=250 y=32 z raised to 2.363||x=70 y=32 z raised to 2.749|
|x=196 y=10 z raised to 1.799||x=196 y=90 z raised to 1.41|
In the following table I have made similar changes to the position of the target. It is not necessary to change the z co-ordinate of the target to keep water in view, because it is the height of the camera above the water level which determines whether water is visible. The altitude of the target determines whether we are looking up or down, and this we will look at on the next page when we consider the camera orientation.
|Target x=80 y=141||Target x=200 y=141|
|target x=167 y=170||Target x=167 y=200|
On the next page we shall look at the camera orientation and the camera settings.