Fixes and changes for functions in LuaBody/Player/Ship

Rewrite of GetAltitudeRelTo:
1. This function is moved to body class to support this functionality in C++ code;
2. This function is used in the LUA version of GetAltitudeRelTo, GetGroundPosition and GetGPS for consistency in calculating altitudes;
3. This function supports the choice of which height to calculate (sea level, above ground).

Other change:
1. GetGPS is moved to Ship.lua to support this function for other ships, not only the player. Implementing this function in C++ is considered unnecessary because of slightly different parameter interface and because of this can be simplified a lot;
2. GetGroundPosition also supports the choice of which altitude to calculate (sea level or above terrain).

Fixes for this issues:

1. GetAltitudeRelTo using player pos no matter what first argument is passed;
2. GetGroundPosition returns nil when not in the rotating frame of ref;
3. GetGPS sometimes return different height than GetAltitudeRelTo;
4. Access violation when trying to access frameBody, frameRotation and call GetGroundPosition when body doesn't have frame of ref (ex. when ship is hyperspacing).

Co-Authored-By: Webster Sheets <[email protected]>

data/libs/Ship.lua

@@ -668,6 +668,40 @@ function Ship:OnScoopCargo(cargoType)
 	return success
 end
 
+
+--
+-- Method: GetGPS
+--
+-- Get altitude, speed, and position of a ship
+--
+-- > alt, vspd, lat, long = ship:GetGPS()
+--
+-- Returns:
+--
+--   alt - altitude
+--
+--   vspd - vertical speed
+--
+--   lat - latitude
+--
+--   lon - longitude
+--
+-- Availability:
+--
+--   November, 2023
+--
+-- Status:
+--
+--   experimental
+--
+function Ship:GetGPS()
+   local lat, lon, altitude = self:GetGroundPosition()
+   local vspd = self:GetVelocityRelTo(self.frameBody):dot(self:GetPositionRelTo(self.frameBody):normalized())
+   lat = math.rad2deg(lat)
+   lon = math.rad2deg(lon)
+   return altitude, vspd, lat, lon
+end
+
 --
 -- Method: Enroll
 --

data/meta/CoreObject/Body.meta.lua

@@ -81,11 +81,12 @@ function Body:DistanceTo(otherBody) end
 
 --- Get the body's position relative to its parent frame.
 ---
---- If the parent is a TerrainBody, altitude will be the height above terrain in meters.
+--- If the parent is a TerrainBody, altitude will be the height above terrain or sea level in meters.
+---@param boolean? terrainRelative
 ---@return number latitude the latitude of the body in radians
 ---@return number longitude the longitude of the body in radians
----@return number? altitude altitude above the ground in meters
-function Body:GetGroundPosition() end
+---@return number? altitude altitude above the ground or sea level in meters
+function Body:GetGroundPosition(terrainRelative) end
 
 --- Find the nearest object of a <Constants.PhysicsObjectType> type
 ---@param type PhysicsObjectType
@@ -104,11 +105,12 @@ function Body:GetPositionRelTo(other) end
 
 --- Get the body's altitude relative to another body.
 ---
---- Returns height above terrain if the other body is a TerrainBody or
+--- Returns height above terrain or sea level if the other body is a TerrainBody or
 --- distance between bodies otherwise.
 ---@param other Body
+---@param boolean? terrainRelative
 ---@return number altitude
-function Body:GetAltitudeRelTo(other) end
+function Body:GetAltitudeRelTo(other, terrainRelative) end
 
 ---@return number
 function Body:GetPhysicalRadius() end

src/Body.cpp

@@ -259,6 +259,36 @@ vector3d Body::GetVelocityRelTo(const Body *relTo) const
 	return GetVelocityRelTo(relTo->m_frame) - relTo->GetVelocityRelTo(relTo->m_frame);
 }
 
+double Body::GetAltitudeRelTo(const Body* relTo, AltitudeType altType)
+{
+	vector3d pos = GetPositionRelTo(relTo);
+	double center_dist = pos.Length();
+	if (relTo && relTo->IsType(ObjectType::TERRAINBODY)) {
+		const TerrainBody* terrain = static_cast<const TerrainBody*>(relTo);
+		vector3d surface_pos = pos.Normalized();
+		double radius;
+		if (altType != AltitudeType::DEFAULT)
+		{
+			radius = altType == AltitudeType::SEA_LEVEL ? terrain->GetSystemBody()->GetRadius() :
+				terrain->GetTerrainHeight(surface_pos);
+		}
+		else
+		{
+			radius = terrain->GetSystemBody()->GetRadius();
+			if (center_dist <= 3.0 * terrain->GetMaxFeatureRadius()) {
+				radius = terrain->GetTerrainHeight(surface_pos);
+			}
+		}
+		double altitude = center_dist - radius;
+		if (altitude < 0)
+			altitude = 0;
+		return altitude;
+	}
+	else {
+		return center_dist;
+	}
+}
+
 void Body::OrientOnSurface(double radius, double latitude, double longitude)
 {
 	vector3d up = vector3d(cos(latitude) * cos(longitude), sin(latitude) * cos(longitude), sin(longitude));

src/Body.h

@@ -43,6 +43,13 @@ enum class ObjectType { // <enum name=PhysicsObjectType scope='ObjectType' publi
 	HYPERSPACECLOUD // <enum skip>
 };
 
+enum class AltitudeType { // <enum name=AltitudeType scope='AltitudeType' public>
+	//SEA_LEVEL if distant, ABOVE_TERRAIN otherwise
+	DEFAULT,
+	SEA_LEVEL,
+	ABOVE_TERRAIN
+};
+
 #define OBJDEF(__thisClass, __parentClass, __TYPE)                                  \
 	static constexpr ObjectType StaticType() { return ObjectType::__TYPE; }         \
 	static constexpr ObjectType SuperType() { return __parentClass::StaticType(); } \
@@ -175,6 +182,7 @@ class Body : public DeleteEmitter, public PropertiedObject {
 	vector3d GetInterpPositionRelTo(FrameId relToId) const;
 	vector3d GetInterpPositionRelTo(const Body *relTo) const;
 	matrix3x3d GetInterpOrientRelTo(FrameId relToId) const;
+	double GetAltitudeRelTo(const Body* relTo, AltitudeType altType = AltitudeType::DEFAULT);
 
 	// should set m_interpolatedTransform to the smoothly interpolated value
 	// (interpolated by 0 <= alpha <=1) between the previous and current physics tick

src/enum_table.cpp

@@ -35,6 +35,13 @@ const struct EnumItem ENUM_PhysicsObjectType[] = {
 	{ 0, 0 },
 };
 
+const struct EnumItem ENUM_AltitudeType[] = {
+	{ "DEFAULT", int(AltitudeType::DEFAULT) },
+	{ "SEA_LEVEL", int(AltitudeType::SEA_LEVEL) },
+	{ "ABOVE_TERRAIN", int(AltitudeType::ABOVE_TERRAIN) },
+	{ 0, 0 },
+};
+
 const struct EnumItem ENUM_ShipAIError[] = {
 	{ "NONE", int(Ship::AIERROR_NONE) },
 	{ "GRAV_TOO_HIGH", int(Ship::AIERROR_GRAV_TOO_HIGH) },
@@ -308,6 +315,7 @@ const struct EnumItem ENUM_ShipControllerFlightControlState[] = {
 
 const struct EnumTable ENUM_TABLES[] = {
 	{ "PhysicsObjectType", ENUM_PhysicsObjectType },
+	{ "AltitudeType", ENUM_AltitudeType },
 	{ "ShipAIError", ENUM_ShipAIError },
 	{ "ShipFlightState", ENUM_ShipFlightState },
 	{ "ShipJumpStatus", ENUM_ShipJumpStatus },
@@ -338,6 +346,7 @@ const struct EnumTable ENUM_TABLES[] = {
 
 const struct EnumTable ENUM_TABLES_PUBLIC[] = {
 	{ "PhysicsObjectType", ENUM_PhysicsObjectType },
+	{ "AltitudeType", ENUM_AltitudeType },
 	{ "ShipAIError", ENUM_ShipAIError },
 	{ "ShipFlightState", ENUM_ShipFlightState },
 	{ "ShipJumpStatus", ENUM_ShipJumpStatus },

src/enum_table.h

@@ -17,6 +17,7 @@ struct EnumTable {
 };
 
 extern const struct EnumItem ENUM_PhysicsObjectType[];
+extern const struct EnumItem ENUM_AltitudeType[];
 extern const struct EnumItem ENUM_ShipAIError[];
 extern const struct EnumItem ENUM_ShipFlightState[];
 extern const struct EnumItem ENUM_ShipJumpStatus[];