## Terragen Coordinate System?

Started by PabloMack, March 20, 2010, 03:55:15 pm

#### PabloMack

##### March 20, 2010, 03:55:15 pm
I have been trying to understand the coordinate system of TG2.  The User Guide states that the +Y is upwards (with -Y downwards) but it doesn't say what the X and Z are.  In LightWave, you are looking in the horizontal direction of +Z and -Z is behind you.  +X is to your right while -X is to you left so that the X & Y axes are just like you are used to seeing them if you put a graph in front of the camera.  Does TG2 do this the same way?

#### Matt

##### March 20, 2010, 06:16:11 pm #1
Yes, TG2 uses the same coordinate system as Lightwave. When +X is to the right and +Y is up, +Z is pointing in the direction you are looking. This is a "left-handed" coordinate system.
Just because milk is white doesn't mean that clouds are made of milk.

#### cyphyr

##### March 21, 2010, 08:53:18 am #2
However
Terragen is XYZ PHB
Lightwave is: XYZ HPB

Richard
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#### PabloMack

##### March 21, 2010, 10:25:02 am #3
Thank you Matt and cyphyr for the info.  Does HPB vs PHB have any significance beyond the order they are listed?

#### Henry Blewer

##### March 21, 2010, 10:39:33 am #4
Pitch, Heading, and Bank. Pitch is up and down. Heading is the direction, and Bank is the angle from the horizon as you travel a direction.
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Forget Tuesday; It's just Monday spelled with a T

#### kevnar

##### March 21, 2010, 09:25:43 pm #5
BUt what happens if you rotate your camera 90 degrees? Which directions are X and Z then? Is it fixed to the terrain (x = north/south, z = east/west), or is it fixed to the camera angle (z is always forward no matter which direction you're pointing)? I imagine it would have to be the first option. Please explain in more depth. Thanks.

#### Henry Blewer

##### March 21, 2010, 11:15:48 pm #6
The heading is like a compass direction. The pitch is up or down from the horizon line. Bank is like holding your hand straight out in front of you. Flare your fingers and have you thumb sticking out, but facing inwards. Now when you rotate your arm, your thumb moves up or down. This is bank.

I do not worry about setting pitch and bank until the camera path is made. It helps keep the confusion down. When you are happy with the camera path, go to the keyframes where you want to look at something to one side. Now you can rotate the camera to look at this area of interest. Just update the keyframe.

http://flickr.com/photos/njeneb/
Forget Tuesday; It's just Monday spelled with a T

#### PabloMack

##### October 17, 2013, 09:37:03 pm #7 Last Edit: November 05, 2013, 12:14:39 pm by PabloMack
Quote from: Matt on March 20, 2010, 06:16:11 pmYes, TG2 uses the same coordinate system as Lightwave. When +X is to the right and +Y is up, +Z is pointing in the direction you are looking. This is a "left-handed" coordinate system.

Time for another one of my ranting narratives! This one is written with tongue-in-cheek sarcasm so please don't be offended.

I have thought a lot about this and it has even given me inspiration to write a satire about this whole standards issue. In my opinion, the mathematicians failed to anticipate the predominant uses of a 3D coordinate system. When these hunch-baked old codgers planned their lectures back in their offices, they laid their lecture note papers flat on their desks and defined their coordinate system. They defined X & Y to be horizontal because their paper was horizonal. They didn't get to the third dimension until later. Z was then defined to be vertical out of the paper as the paper is laying horizontally on the desk. But what is the first thing they did when they drew their graph on the black board for the students to see it? They drew the Y going up expecting their students to understand that they are supposed to be imagining the professor back in his office with the graph laying flat on his desk! Instead, the students went away from the lecture thinking in terms of the black board and not the professor's notes WHICH THEY NEVER SAW BY THE WAY, duhhhh! They also expect for us to interpret right-handedness the way they do. If I take my right hand and define the X to be my middle finger, my pointer finger to be the Y axis and the Z to be my thumb then I have a "left-handed system"? I used my right hand to do this. How can that be? Who says I have to respect the mathematicians and recognize their finger labelling system? I have used my right hand to define the coordinate system used in Lightwave and Terragen!

The British and the Americans can both claim that the side of the road they drive on follows the "right-hand rule". The British put the steering wheel on the right side of the car and the Americans drive on the right side of the road. Well, how do most of us experience the world in real life? We look forward, not down at a desk. We watch television facing a horizontal direction, not looking up at us. The world around us is, for the most part, a 360° horizontal panarama around us. We do not live our lives looking up or down. Only on occation do we deviate from looking around us in the horizontal. Also, the forward direction is positive, not negative. Most of us have cars that have four or five gears to go forward and only one to go backward. So forward is meant to be positive, not negative like the mathematicians would have us believe. The spedometers never read -60 when we are traveling down the highway. We do not drive backwards in order to obey the rules laid down for us by excentric mathematicians who don't understand that the rest of us use numbers with actual units like the physicists do. So to sum it up, Lightwave and Terragen corrected a gross error committed by the mathematicians long before there was television, computer screens and cars. This is the way I look at the problem because I am a right-handed person. They have offended me because they want to dictate to me how to define right-handedness. Those of you who are left-handed may have no problem with the mathematicians's mistake because you believe that left-handedness was the correct way all along.