Difference between revisions of "Planet"
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[[Category: Object Nodes
[[Category: Object Nodes]]
Revision as of 18:46, 1 June 2011
Node Description and Purpose:
The Planet object is the basis for most scenes in TG2. It is the terrain surface and the atmosphere is created around it.
TG2 can handle zooming into a planet from way out in "space" to very close to the planet surface. However if the scene you're creating is on a kind of local scale rather than planetary scale we recommend that you create the scene around the origin of the planet, which is effectively the North Pole. As you move a long way from the origin coordinates begin to lose accuracy and you might start to see things you're not expecting. In many cases this isn't a problem and creating the scene close to the origin works well.
It does however mean that even though TG2 can model whole planets if you want to model a real world location it isn't necessarily a good idea to put that location in the same location as it is in the real world. For example let's say you wanted to model an area in the South Island of New Zealand. If you used the real position on the planet, low down in the Southern Hemisphere, you would likely find problems with coordinate accuracy. It would be much better to reposition the location at the North Pole.
To help with this if you're using georeferenced data you can set the latitude and longitude of the planet origin. This effectively remaps that position to the planet origin where accuracy is better.
You can have multiple planets in a scene. For example to create a moon you can make a new Planet object and position and size it appropriately. Here are some sizes of planets etc. in our solar system:
- The Moon: 1738000 m
- Mercury: 2439000 m
- Venus: 6052000 m
- Earth (default planet size): 6378000 m
- Mars: 3397000 m
- Jupiter: 71490000 m
- Saturn: 60268000 m
- Uranus: 2559000 m
- Neptune: 25629000 m
- Pluto: 1160000 m
Node Type: Object
- Show b-box in preview: If this is checked the bounding box of the planet is shown in the 3D Preview.
- Render surface: This setting will turn off rendering of the planet surface, leaving only the atmosphere (if that's turned on).
- Render atmospher: This setting can turn off rendering of the planet atmosphere.
- Lat long at apex: This setting controls the latitude and longitude at the apex or origin of the planet. By default this is set to 0,0 which corresponds to the North Pole on Earth. As mentioned above coordinate accuracy can get worse as you move away from apex. If you are using georeferenced data you can use an appropriate latitude and longitude to remap your area of interest to the origin which will help to avoid accuracy problems.
- Centre: This sets the position of the centre of the planet. As this can involve very large distances numbers here are often represented in scientific notation.
- Rotation: This sets the rotation of the planet about its centre.
- Radius: This sets the radius of the planet. By default it's set to the radius of Earth (6378 km). The radius is set in metres. As this can involve very large numbers values here are often represented in scientific notation.
- Import chan file: Click this button to import a chan file to animate the position and rotation of the Planet.
- Heading: TBC
- Elevation: TBC
- Distance: TBC
- Surface shader: This sets the shader that creates the planet surface. Typically this will be bottom of the chain of nodes creating the surface layers and terrain of the planet.
- Atmosphere shader: This sets the shader which creates the atmosphere of the planet. This will normally be the bottom of the chain of atmosphere and cloud shaders creating the atmosphere for the planet.
- Displacement tolerance: TBC
The bounding box is a box which surrounds (or bounds) an object or shader. This box shows the maximum extents of the item inside it. Sometimes abbreviated as "b-box".
A shader is a program or set of instructions used in 3D computer graphics to determine the final surface properties of an object or image. This can include arbitrarily complex descriptions of light absorption and diffusion, texture mapping, reflection and refraction, shadowing, surface displacement and post-processing effects. In Terragen 2 shaders are used to construct and modify almost every element of a scene.