# simorbit.sml

# Script for TNTsim3D that gets the current viewer position and the position on the
# terrain at the center of the view, then orbits the viewer clockwise around that
# terrain position.

#####################################################################################
###  For a script to run under TNTsim3D, it must include an instance of
###  class TNTSIM3D named "TNTsim3D".  The script must also be saved as an RVC
###  object in the TNTsim3D Landscape File you want to run it with.
#####################################################################################

# declare class instance for TNTsim3D interface class
class TNTSIM3D TNTsim3D;

# variable declarations
class POINT3D viewer, center, orientation;
numeric roll;			# roll angle from horizontal (degrees)
numeric radius;		# radius of orbit (meters)
numeric heading;		# heading of viewer in azimuth (counter-clockwise from north)
numeric direction;	# direction of view in internal cartesian coordinate system
							# (degrees clockwise from X axis)

#######################################################################
### get viewer and center positions from current scene and center projected
### onto terrain surface to get coordinates for orbit center 
#######################################################################
TNTsim3D.GetScene(viewer, center, roll);
TNTsim3D.GetProjectedCenter(center);

## compute radius from center of orbit
radius = sqrt( sqr(viewer.x - center.x) + sqr(viewer.y - center.y) );

#######################################################################
### get viewer position and orientation from current scene to
### get present heading
####################################################################### 
TNTsim3D.GetSceneByOrientation(viewer, orientation);
heading = orientation.z;	# azimuth angle from viewer toward center in degrees
									# clockwise from north

# reverse heading and convert to direction angle (counter-clockwise from x axis)
# to compute next viewer position in orbit
direction = 180 - (heading - 90);
if (direction > 0) then
	direction = direction - 360;


########################################################################
### SML function name predefined in TNTsim3D, called for each frame.
########################################################################
func OnFrame()
	{
	# decrement direction
	direction = direction - 0.2;
	if (direction < 0) then
		direction = direction - 360;

	# compute new viewer x and y position from direction angle
	viewer.x = center.x + (radius * cosd(direction) );
	viewer.y = center.y + (radius * sind(direction) );

	# set scene with new viewer position and center on orbit center, with roll = 0
	TNTsim3D.SetScene(viewer, center, 0);
	}