fgTie(x("/sim/current-view/view_or_offset"), this,
&FGViewMgr::getCurrentViewOrOffset);
- fgTie(x("/sim/current-view/view1200"), this,
- &FGViewMgr::getCurrentView1200);
+ fgTie(x("/sim/current-view/view_frame"), this,
+ &FGViewMgr::getCurrentViewFrame);
SGPropertyNode *n = fgGetNode("/sim/current-view", true);
n->tie("viewer-x-m", SGRawValuePointer<double>(&abs_viewer_position[0]));
axis_lat = axis;
}
-static const char* fmt("%6.3f ; %6.3f %6.3f %6.3f");
-
-// current view orientation
-// This is a rotation relative to the earth-centered (ec)
-// refrence frame.
-// However, the components of this quaternion are expressed
-// in the OpenGL camera system i.e. x-right, y-up, z-back.
-const char* FGViewMgr::getCurrentViewOrientation() const{
- return str(boost::format(fmt)
- % current_view_orientation.w()
- % current_view_orientation.x()
- % current_view_orientation.y()
- % current_view_orientation.z() ).c_str();
-}
-
-// This rotation takes you from the 12:00 direction
-// i.e. body attitude
-// to whatever the current view direction is.
+// Convert a quat to a string.
+// We assume the quat is being used as a rotor, so we
+// coerce it to standard rotor form, making the scalar
+// part non-negative, to eliminate double coverage of
+// the rotation group.
+// The format is "w ; x y z" with a semicolon separating
+// the scalar part from the bivector components.
+const char* format_rotor(const SGQuatd _quat){
+ SGQuatd quat(_quat);
+ if (quat.w() < 0.) quat *= -1.; // remove double coverage
+ return str(boost::format("%6.3f ; %6.3f %6.3f %6.3f")
+ % quat.w()
+ % quat.x()
+ % quat.y()
+ % quat.z() ).c_str();
+}
+
+// reference frame orientation.
+// This is the view orientation you get when you have no
+// view offset, i.e. the offset operator is the identity.
+//
+// For example, in the familiar "cockpit lookfrom" view,
+// the reference frame is equal to the aircraft attitude,
+// i.e. it is the view looking towards 12:00 straight ahead.
+//
+// FIXME: Somebody needs to figure out what is the reference
+// frame view for the other view modes.
+//
+// Conceptually, this quat represents a rotation relative
+// to the ECEF reference orientation, as described at
+// http://www.av8n.com/physics/coords.htm#sec-orientation
+//
+// See the NOTE concerning reference orientations, below.
+//
+// The components of this quat are expressed in
+// the conventional aviation basis set,
+// i.e. x=forward, y=starboard, z=bottom
+const char* FGViewMgr::getCurrentViewFrame() const{
+ return format_rotor(current_view_orientation * conj(fsb2sta)
+ * conj(current_view_or_offset) );
+}
+
+// view offset.
+// This rotation takes you from the aforementioned
+// reference frame view orientation to whatever
+// actual current view orientation is.
+//
// The components of this quaternion are expressed in
-// the XYZ body frame.
+// the conventional aviation basis set,
+// i.e. x=forward, y=starboard, z=bottom
const char* FGViewMgr::getCurrentViewOrOffset() const{
- return str(boost::format(fmt)
- % current_view_or_offset.w()
- % current_view_or_offset.x()
- % current_view_or_offset.y()
- % current_view_or_offset.z() ).c_str();
+ return format_rotor(current_view_or_offset);
}
-// This rotates the conventional aviation XYZ body system
-// i.e. x-forward, y-starboard, z-bottom
-// to the OpenGL camera system
-// i.e. x-right, y-up, z-back.
-const SGQuatd q(-0.5, -0.5, 0.5, 0.5);
-
-// The current attitude of the aircraft,
-// i.e. the 12:00 direction.
-// The components of this quaternion are expressed in
-// the GL camera frame.
-const char* FGViewMgr::getCurrentView1200() const{
- SGQuatd view1200 = current_view_orientation
- * conj(q) * conj(current_view_or_offset) * q;
- return str(boost::format(fmt)
- % view1200.w()
- % view1200.x()
- % view1200.y()
- % view1200.z() ).c_str();
+// current view orientation.
+// This is a rotation relative to the earth-centered (ec)
+// reference frame.
+//
+// NOTE: Here we remove a factor of fsb2sta so that
+// the components of this quat are displayed using the
+// conventional ECEF basis set. This is *not* the way
+// the view orientation is stored in the views[] array,
+// but is easier for most people to understand.
+// If we did not remove this factor of fsb2sta here and
+// in getCurrentViewFrame, that would be equivalent to
+// the following peculiar reference orientation:
+// Suppose you are over the Gulf of Guinea, at (lat,lon) = (0,0).
+// Then the reference frame orientation can be achieved via:
+// -- The aircraft X-axis (nose) headed south.
+// -- The aircraft Y-axis (starboard wingtip) pointing up.
+// -- The aircraft Z-axis (belly) pointing west.
+// To say the same thing in other words, and perhaps more to the
+// point: If we use the OpenGL camera orientation conventions,
+// i.e. Xprime=starboard, Yprime=top, Zprime=aft, then the
+// aforementioned peculiar reference orientation at (lat,lon)
+// = (0,0) can be described as:
+// -- aircraft Xprime axis (starboard) pointed up
+// -- aircraft Yprime axis (top) pointed east
+// -- aircraft Zprime axis (aft) pointed north
+// meaning the OpenGL axes are aligned with the ECEF axes.
+const char* FGViewMgr::getCurrentViewOrientation() const{
+ return format_rotor(current_view_orientation * conj(fsb2sta));
}
void
projects / flightgear.git / commitdiff