Object following the surface of a sphere

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JohnStabler

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Joined: 16th Aug 2013

Location: Cardiff, Wales, UK

Posted: 29th Jul 2016 21:45 Edited at: 30th Jul 2016 10:20

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Hi,

I'm trying to make an object fly around, as if it were subject to a planet's gravity. It works, until the ship reaches one of the poles. Anyone know what I'm doing wrong or how to fix it?

SetErrorMode(2)

// set window properties
SetWindowTitle( "Test" )
SetWindowSize(1280, 720, 0)

// set display properties
SetVirtualResolution(1280, 720)
SetOrientationAllowed( 1, 1, 1, 1 )

global ship
global sphere

sphere = CreateObjectSphere(190, 64, 64)
ship = CreateObjectBox(5, 5, 5)
SetObjectColor(ship, 255, 0, 0, 255)
SetObjectPosition(ship, 0, 0, -105)

SetObjectLookAt(ship, 0, 0, 0, 0)
RotateObjectLocalY(ship, 90)
RotateObjectLocalY(ship, 45)

SetCameraPosition(1, 0, 0, -300)
SetCameraLookAt(1, 0, 0, 0, 0)

do

UpdateShip()

Print( ScreenFPS() )
    Sync()
loop

function UpdateShip()

MoveObjectLocalZ(ship, 1)
	ray = ObjectRayCast(sphere, GetObjectX(ship), GetObjectY(ship), GetObjectZ(ship), 0, 0, 0)

if ray = 1

ray = GetObjectRayCastHitID(0)

nx# = GetObjectRayCastNormalX(0)
		ny# = GetObjectRayCastNormalY(0)
		nz# = GetObjectRayCastNormalZ(0)

StableZ(ship, nx#, ny#, nz#)
		StableX(ship, nx#, ny#, nz#)

rx# = GetObjectRayCastX(0)
		ry# = GetObjectRayCastY(0)
		rz# = GetObjectRayCastZ(0)

SetObjectPosition(ship, rx# + (nx# * 5.0), ry# + (ny# * 5.0), rz# + (nz# * 5))

SetObjectLookAt(ship, rx#, ry#, rz#, 0)

RotateObjectLocalX(ship, -90.0)
		RotateObjectLocalY(ship, 0)

endif

//SetCameraPosition(1, GetObjectX(ship), GetObjectY(ship), GetObjectZ(ship))
	//SetCameraRotation(1, GetObjectAngleX(ship), GetObjectAngleY(ship), GetObjectAngleZ(ship))

endfunction

+ Code Snippet

SetErrorMode(2)

// set window properties
SetWindowTitle( "Test" )
SetWindowSize(1280, 720, 0)

// set display properties
SetVirtualResolution(1280, 720)
SetOrientationAllowed( 1, 1, 1, 1 )

global ship
global sphere

sphere = CreateObjectSphere(190, 64, 64)
ship = CreateObjectBox(5, 5, 5)
SetObjectColor(ship, 255, 0, 0, 255)
SetObjectPosition(ship, 0, 0, -105)

SetObjectLookAt(ship, 0, 0, 0, 0)
RotateObjectLocalY(ship, 90)
RotateObjectLocalY(ship, 45)

SetCameraPosition(1, 0, 0, -300)
SetCameraLookAt(1, 0, 0, 0, 0)

do

	UpdateShip()

    Print( ScreenFPS() )
    Sync()
loop


function UpdateShip()

	MoveObjectLocalZ(ship, 1)
	ray = ObjectRayCast(sphere, GetObjectX(ship), GetObjectY(ship), GetObjectZ(ship), 0, 0, 0)

	if ray = 1

		ray = GetObjectRayCastHitID(0)

		nx# = GetObjectRayCastNormalX(0)
		ny# = GetObjectRayCastNormalY(0)
		nz# = GetObjectRayCastNormalZ(0)

		StableZ(ship, nx#, ny#, nz#)
		StableX(ship, nx#, ny#, nz#)

		rx# = GetObjectRayCastX(0)
		ry# = GetObjectRayCastY(0)
		rz# = GetObjectRayCastZ(0)

		SetObjectPosition(ship, rx# + (nx# * 5.0), ry# + (ny# * 5.0), rz# + (nz# * 5))

		SetObjectLookAt(ship, rx#, ry#, rz#, 0)

		RotateObjectLocalX(ship, -90.0)
		RotateObjectLocalY(ship, 0)

	endif

	//SetCameraPosition(1, GetObjectX(ship), GetObjectY(ship), GetObjectZ(ship))
	//SetCameraRotation(1, GetObjectAngleX(ship), GetObjectAngleY(ship), GetObjectAngleZ(ship))

endfunction

Thanks,
John

Hi. I am a real person (not a bot). I appreciate all replies and advice.

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Ortu

DBPro Master

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Years of Service

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Joined: 21st Nov 2007

Location: Austin, TX

Posted: 29th Jul 2016 22:17 Edited at: 29th Jul 2016 22:24

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My guess, the problem stems from using the sphere's normals, which can be wonky at the poles. Unless it is an icosphere, it won't have a face at the pole and won't give a good normal. This pinching of the geometry is a familiar issue to anyone that has tried to uv map and texture a sphere

Because it is a sphere though, you can just use some maths against the object center

+ Code Snippet

planetx# = GetObjectX (sphere)
planetY# = GetObjectY (sphere)
planetZ# = GetObjectZ (sphere)

d# = cos (orbitAngY#) * orbitDistance#
shipX# = planetX# + sin (orbitAngX#) * d#
shipY# = planetY# + sin (orbitAngY#) * orbitDistance#
shipZ# = planetZ# + cos (orbitAng#) * d#

SetObjectPosition (ship, shipX#, shipY#, shipZ#)

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JohnStabler

AGK Bronze Backer

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Joined: 16th Aug 2013

Location: Cardiff, Wales, UK

Posted: 29th Jul 2016 22:31

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Thanks Ortu. That sounds about right.

I'll use Blender to create an icosphere and use that.

Hi. I am a real person (not a bot). I appreciate all replies and advice.

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JohnStabler

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Joined: 16th Aug 2013

Location: Cardiff, Wales, UK

Posted: 30th Jul 2016 00:31

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Hmm. I just loaded an isosphere instead and I still seem to be getting problems at the poles.

Hi. I am a real person (not a bot). I appreciate all replies and advice.

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JohnStabler

AGK Bronze Backer

11

Years of Service

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Joined: 16th Aug 2013

Location: Cardiff, Wales, UK

Posted: 31st Jul 2016 10:35

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I'm now using maths, rather than raycasting to calculate the orientation and position of the ship. However, I have the same problem of the ship getting stuck. After doing some debugging it has become apparent that depending on the position of the ship, the SetObjectLookat function rotates the ship differently. So, if the ship is at the front of the sphere I need to rotate the ship on the X axis by 90 degrees to make it move perpendicular to the surface. If the ship is at the back of the sphere then I have to rotate it on the X axis by -90 degrees. This is what leads to the ship getting stuck at boundaries.

Any idea how to solve the problem i.e. easily calculate which way to rotate the ship depending on Euler position?

Hi. I am a real person (not a bot). I appreciate all replies and advice.

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