Simplifying surface feature placement

[BillC]

Could SurfaceFixedRotation simply be called Attitude? I suppose that only means the pitch (tilt) and roll. You're trying to describe something like Attitude + Bearing, or Attitude + Azimuth. But still, it wouldn't be entirely incorrect.

[chris]

Could SurfaceFixedRotation simply be called Attitude? I suppose that only means the pitch (tilt) and roll. You're trying to describe something like Attitude + Bearing, or Attitude + Azimuth. But still, it wouldn't be entirely incorrect.

Not entirely . . . but I fear that it would be confusing to have Attitude and Orientation mean different things in Celestia when the words are nearly synonymous in English. It's the best suggestion so far, though.

--Chris

[chris]

Is Body going to be recognized as a keyword? Or is it already?

I suggest making Class "surfacefeature" one of the defaults for a SurfaceObject, too.

Here's my one concern about making surfacefeature the default class: you may want to use SurfaceFeature to place a spacecraft (e.g. MER) on the surface of a planet. Is it strange to call an object a surface feature, then override that by supplying a Class property:

Code: Select all

SurfaceFeature
{
    Class "spacecraft"
    ...
}


Acceptable?

--Chris

[selden]

Having to specify Class "spacecraft" (if that's what the object happens to be) seems reasonable to me.

Otherwise the default would be spacecraft, wouldn't it?
That seems even stranger

[chris]

Here is an attempt to illustrate with screenshots how the Topocentric frame and the FixedAttitude (a name I prefer over SurfaceFixedRotation) work. The Topocentric frame is the default for a SurfaceObject, though it can also be used with other object types.

Here is the topocentric frame in action, all models with the same rotation within their frame:

topo-frame-1.jpg

In the topocentric frame, the z-axis (blue) always points straight up from the surface of a planet, and the y-axis points north.

The FixedAttitude rotation model can be a more intuitive way of orienting a model than FixedRotation. In all of the following images, the transparent axes are the frame axes, and the solid ones are the body axes.

FixedAttitude has three properties: Heading, Tilt, and Roll. The ssc definition of the object in the next image looks like this:

Code: Select all

SurfaceObject "Plane" "Sol/Earth"
{
   Mesh "plane.3ds"
   Radius 1000

   FixedPosition { Planetographic [ -60 30 300 ] }
   FixedAttitude
   {
      Heading 45
      Tilt 0
      Roll 0
   }
}


Heading is the rotation about the z-axis, which points toward the sky in a topocentric frame. In the first image, Heading is set to 45 degrees:

topo-heading-45.jpg

Tilt is the rotation about the x-axis. It is equivalent to pitch in aeronautics. In this image, a Tilt of 30 degrees makes the plane face up toward the sky:

topo-tilt-30.jpg

Finally, here is the effect of a Roll of 30 degrees:

topo-roll-30.jpg

--Chris

[BobHegwood]

For what it's worth here Chris, I think I like these descriptors and the terminology. It almost makes sense to me, so it
should be sparkling clear to anyone else.

[ElChristou]

Here is an attempt to illustrate with screenshots...

Nice! Would you put this in the Wiki or want one of us to do it?

[chris]

Here is an attempt to illustrate with screenshots...

Nice! Would you put this in the Wiki or want one of us to do it?

If you want to do it, I'd sure appreciate the help!

--Chris

[Chuft-Captain]

Tilt is the rotation about the x-axis. It is equivalent to pitch in aeronautics.

As this is the case Chris, then why don't you just use "Pitch" instead of "Tilt", as most people will be familiar with the term and it's meaning/application. (I'd be tempted to go with "Yaw" as well, except that in Celestia, I guess "Heading" is a more useful and intuitive term.

JM2CW, FWIW

CC

[chris]

Tilt is the rotation about the x-axis. It is equivalent to pitch in aeronautics.

As this is the case Chris, then why don't you just use "Pitch" instead of "Tilt", as most people will be familiar with the term and it's meaning/application. (I'd be tempted to go with "Yaw" as well, except that in Celestia, I guess "Heading" is a more useful and intuitive term.

I borrowed terminology from KML, the description language for Google Earth:

http://code.google.com/apis/kml/documen ... html#model

I also think that the meaning of Tilt may be more obvious to some people than Pitch (though not to everyone.)

--Chris

[Chuft-Captain]

Tilt is the rotation about the x-axis. It is equivalent to pitch in aeronautics.

As this is the case Chris, then why don't you just use "Pitch" instead of "Tilt", as most people will be familiar with the term and it's meaning/application. (I'd be tempted to go with "Yaw" as well, except that in Celestia, I guess "Heading" is a more useful and intuitive term.

I borrowed terminology from KML, the description language for Google Earth:

http://code.google.com/apis/kml/documen ... html#model

I also think that the meaning of Tilt may be more obvious to some people than Pitch (though not to everyone.)

--Chris

Fair enough. Whilst consistency with Google Earth's conventions is not necessarily a bad idea, IMO it is of limited value in Celestia. For example "Heading" has an intuitive meaning in Google Earth because it's always "The Earth" they're dealing with, however in Celestia there are other (less specific) circumstances where addon creators might want to specify orientation (eg. orienting component meshes with others), where "Heading" has a less intuitive meaning. ie. where "North" is not so clearly defined.

At the end of the day, what you've done is fine, and I'm not asking you to change it...(they're just "words" after all).
It's just my gut feeling that most addon creators would probably be just as comfortable with the standard aeronautical terminology, which may have a broader and more intuitive meaning in the Celestia context.

Just my opinion anyway.
CC

[duds26]

Then north is just the corresponding axes right?
Can we just use the reference frame or body vectors for orientation as a reference of directions?