Quaternion rips and tricks

position

vector p = llGetPos();
rotation r = llGetRot();
vector newPos = p + <1,0,0>;    //  wrong
vector newPos = p + <1,0,0> * r;  // right
llGetPos() + offset*llGetRot()

rotation r = llGetRot(); // the rotation of one object.

llSetRot(r);   // in the other object, causes it to be rotated the same way.  
llRotLookAt( r, .1, 1);
 brackets so it's nicely highlighted?

I think this has great potential to be a sticky.

vector foo_pos; //equals position of foo in region cords
vector my_pos = llGetPos();

vector axis = <1.0,0.0,0.0>;//which axis to point at foo.
rotation target = llRotBetween(axis, foo_pos - my_pos);
llSetRot(target);

integer x;
float xaxis;
float yaxis;
float xrand;
float yrand;
float mass;
vector turn = <0,0,0>;
vector mypos;

default
{

    state_entry()
    {
        llSay(0, "Ensign, lay in a course for adventure!");
        //llSetStatus(STATUS_ROTATE_X | STATUS_ROTATE_Y | STATUS_ROTATE_Z, FALSE);
        llSetPos(llGetPos() + <0, 0, 0.1>);
        llSetPrimitiveParams([PRIM_PHYSICS, TRUE]);
        mass = llGetMass();

    }

    touch_start(integer total_number)
    {

        llSetTimerEvent(60);
        llSay(0, "Engage!");
        llSetHoverHeight(65, TRUE, 10);
        llApplyImpulse(mass * <-10,0,0>, FALSE);

    }
    timer()
    { 
        xaxis = (llFrand(5));
        yaxis = (llFrand(5));
        xrand = (llCeil(llFrand(10)));
        yrand = (llCeil(llFrand(10))); 
        if (xrand > 5)
            {
                xrand = -xrand;
            }
        if (yrand > 5)
            {
                yrand = -yrand; 
            }        
        llApplyImpulse(mass * < xaxis, yaxis, 0>, FALSE);
        mypos = llGetPos();
        llLookAt(mypos + llGetVel(), mass * 0.5, mass * rotation_modifier);
        llSay (0, "Engage!");
        if (x == 30) 
            {
                llDie();
            }
        else 
            x=x+1;
            llSay (0, (string) x + " Mintues have passed,");
            llSay (0, (string) (30-x)+ " Minutes left till I die.");

    } 
}

vector tgt=llGetPos()+llGetVel();
vecttr pos=llGetPos();

llSetRot( llRotBetween(<1,0,0>, tgt-pos)) );

llSetRot( llRotBetween(<1,0,0>, llGetVel())) ;
vector newPos = p + <1,0,0> * r;  // right

vector newPos = p + llRot2Fwd( r );

integer isTargetInFrontOfMe( rotation myDir, vector myPos, vector targetPos )
{

	// Convert dir and pos to a plane equation
	vector p1 = myPos + <0,1,0> * myDir;
	vector p2 = myPos + <0,0,1> * myDir;
	vector normal = llVecNorm( (p2 - p1) % (myPos - p1) );

	vector dv = llVecNorm( targetPos - p1 );
	float test = normal * dv;

	return (test > 0);

}

integer isTargetFacingMe( vector myPos, vector targetPos, rotation targetDir )
{

	// Convert dir and pos to a plane equation
	vector p1 = targetPos + <0,1,0> * targetDir;
	vector p2 = targetPos + <0,0,1> * targetDir;
	vector normal = llVecNorm( (p2 - p1) % (targetPos - p1) );

	vector dv = llVecNorm( myPos - p1 );
	float test = normal * dv;

	return (test > 0);

}

default
{

	touch_start(integer total_number)
	{
		llOwnerSay( "In front = " + (string)isTargetInFrontOfMe( llGetRot(), llGetPos(), llDetectedPos(0) ) );		
		llOwnerSay( "Facing me = " + (string)isTargetFacingMe( llGetPos(), llDetectedPos(0) , llDetectedRot(0) ) );		
	}

}

	// Convert dir and pos to a plane equation
	vector p1 = myPos + <0,1,0> * myDir;
	vector p2 = myPos + <0,0,1> * myDir;
	vector normal = llVecNorm( (p2 - p1) % (myPos - p1) );

vector normal = llRot2Fwd( myDir );

llRotLookAt(r, f, d);
float test = normal * dv;
return (test > 0);

 vector normal = llRot2Fwd( myDir );

 vector normal = llRot2Fwd( myDir );

integer isTargetFacingMe( vector myPos, vector targetPos, rotation targetDir )
{

	vector normal = llRot2Fwd( targetDir ); 
	vector dv = llVecNorm( myPos - targetPos );
	float test = normal * dv;

	return (test > 0);

}

Quaternion rips and tricks
Lee Ponzu What Would Steve Do? Join date: 28 Jun 2006 Posts: 1,770	12-17-2006 10:01 Like a lot of people, I've been struggling with lsl rotations, aka quaternions. I've googled and wiki'd and experimented. I feel like I am finally starting to get a grip... Below, I will post a solution to a simple but real problem that I wrestled with. It appears elsewhere, but I will put it here. My idea is that others will post their solutions to LSL problems involving rotations, vectors, and closely related issues, so that this might someday evolve into a sticky.
Lee Ponzu What Would Steve Do? Join date: 28 Jun 2006 Posts: 1,770	Finding a point offset from current position 12-17-2006 10:27 Often, you have an object that has a current position and rotation. You need to calculate a new point that is offset from that object, for example 1 meter directly ahead. Here's a way to do it, plus an explanation of how it works. An object Foo has a current position that can be retrieved using CODE vector p = llGetPos(); This returns the position of Foo in world coordinates. Foo also has a rotation that represents its heading or orientation with respect to the world coordinates. CODE rotation r = llGetRot(); This r is the infamous quaternion. For LSL purposes, you might not need to understand all the underlying math. It is just the rotation represented in 4 numbers. Note that by definition, Foo's x coordinate is forward, the y coordinate is to the left, and the z coordinate is up. This is a so-called right hand system. Point in the x direction, point your middle finger at right angles in the y direction, and then your thumb points up. From the point of view of Foo, he vector representing "1 meter ahead" is <1,0,0>, but this vector is in local coordinates. If you click the Local in the Object Editor, the x-axis is by definition the "front" of the object. These are the local axes. When World is selected, the region axes are shown. Suppose you tried to compute the desired new possition by CODE vector newPos = p + <1,0,0>; // wrong The problem is that this adds 1 meter to the current position of Foo in the world coordinates, which is 1 meter to the East, no matter how the object is rotated. This is where the magic of quaternions comes in. If we multiply a local vector on the right by the object's rotation, it is converted into the needed world vector. So, what we need is CODE vector newPos = p + <1,0,0> * r; // right The position, p, is already in world coordinates. <1,0,0> is in local coordinates, and multiplying it on the right by the rotation, r, converts it to world. (On the left would not work. That's the way quaternions are.) Suppose you need a point offset differently, such as 1 meter ahead, but 2 meters higher. Then use <1,0,2> as the offset in local coordinates. In general CODE llGetPos() + offset*llGetRot() will be the point offset in local coordinates from the current position. I hope this is right. Other examples welcome.
Lee Ponzu What Would Steve Do? Join date: 28 Jun 2006 Posts: 1,770	Lining up 12-17-2006 10:29 If you want to objects to be oriented the same way, you can use the rotations. CODE rotation r = llGetRot(); // the rotation of one object. llSetRot(r); // in the other object, causes it to be rotated the same way. That is, local x, y, and z axes will be the same. However, this is for non-pysical objects, and is more or less instantaneous. For physical objects, try something like CODE llRotLookAt( r, .1, 1); Can be used. The rotation is the same. The second parameter is how fast it rotates, and the third is how quickly it stops rotating once it gets there.
Strife Onizuka Moonchild Join date: 3 Mar 2004 Posts: 5,887	12-17-2006 10:40 May i suggest you put any code snippets in CODE brackets so it's nicely highlighted? I think this has great potential to be a sticky. _____________________ Truth is a river that is always splitting up into arms that reunite. Islanded between the arms, the inhabitants argue for a lifetime as to which is the main river. - Cyril Connolly Without the political will to find common ground, the continual friction of tactic and counter tactic, only creates suspicion and hatred and vengeance, and perpetuates the cycle of violence. - James Nachtwey
Lee Ponzu What Would Steve Do? Join date: 28 Jun 2006 Posts: 1,770	Rotate to face a point 12-17-2006 10:41 Suppose you have an <x,y,z> point in world coordinates, and an object's Foo. You want Foo to rotate to face the point. You need to calculate the rotation needed to convert Foo's rotation by. I don't feel that I have a good solution to this. Any advice welcome.
Strife Onizuka Moonchild Join date: 3 Mar 2004 Posts: 5,887	12-17-2006 10:50 CODE vector foo_pos; //equals position of foo in region cords vector my_pos = llGetPos(); vector axis = <1.0,0.0,0.0>;//which axis to point at foo. rotation target = llRotBetween(axis, foo_pos - my_pos); llSetRot(target); _____________________ Truth is a river that is always splitting up into arms that reunite. Islanded between the arms, the inhabitants argue for a lifetime as to which is the main river. - Cyril Connolly Without the political will to find common ground, the continual friction of tactic and counter tactic, only creates suspicion and hatred and vengeance, and perpetuates the cycle of violence. - James Nachtwey
Vares Solvang It's all Relative Join date: 26 Jan 2005 Posts: 2,235	12-17-2006 11:48 I have a "wander'n cube" that I made up that uses neutral buoyancy to float and then just applied an impulse in a random direction every now and then. It works fine and is fun to just wander around sl on, but I have never been able to figure out a way to make it rotate to face the new, random direction that the impulse is applied too. Do you know a way to do this? Here is the code I used. The llLookAt line didn't work btw (of course). Please note this was just something I banged together one night while I was bored and is in no way "finished" code. : CODE integer x; float xaxis; float yaxis; float xrand; float yrand; float mass; vector turn = <0,0,0>; vector mypos; default { state_entry() { llSay(0, "Ensign, lay in a course for adventure!"); //llSetStatus(STATUS_ROTATE_X \| STATUS_ROTATE_Y \| STATUS_ROTATE_Z, FALSE); llSetPos(llGetPos() + <0, 0, 0.1>); llSetPrimitiveParams([PRIM_PHYSICS, TRUE]); mass = llGetMass(); } touch_start(integer total_number) { llSetTimerEvent(60); llSay(0, "Engage!"); llSetHoverHeight(65, TRUE, 10); llApplyImpulse(mass * <-10,0,0>, FALSE); } timer() { xaxis = (llFrand(5)); yaxis = (llFrand(5)); xrand = (llCeil(llFrand(10))); yrand = (llCeil(llFrand(10))); if (xrand > 5) { xrand = -xrand; } if (yrand > 5) { yrand = -yrand; } llApplyImpulse(mass * < xaxis, yaxis, 0>, FALSE); mypos = llGetPos(); llLookAt(mypos + llGetVel(), mass * 0.5, mass * rotation_modifier); llSay (0, "Engage!"); if (x == 30) { llDie(); } else x=x+1; llSay (0, (string) x + " Mintues have passed,"); llSay (0, (string) (30-x)+ " Minutes left till I die."); } } _____________________
Lee Ponzu What Would Steve Do? Join date: 28 Jun 2006 Posts: 1,770	Untested solution to Vera's problem 12-17-2006 12:26 So, this problem is, make the rotation of an object line up with it's velocity. llGetPos() + llGeVel() is a point in world coordinates, just like the previous problem. That's where your object is headed. To make the x-axis point at that point, try CODE vector tgt=llGetPos()+llGetVel(); vecttr pos=llGetPos(); llSetRot( llRotBetween(<1,0,0>, tgt-pos)) ); Looking at the math, that turns out to be CODE llSetRot( llRotBetween(<1,0,0>, llGetVel())) ;
Vares Solvang It's all Relative Join date: 26 Jan 2005 Posts: 2,235	12-17-2006 16:43 I replaced the llLookAt line with your code, but I still don't rotate at all when the random impulse is applied. Does this kind of code only work if you are using if you are using llSetVel type code with it? _____________________
Joannah Cramer Registered User Join date: 12 Apr 2006 Posts: 1,539	12-17-2006 18:11 From: Lee Ponzu The problem is that this adds 1 meter to the current position of Foo in the world coordinates, which is 1 meter to the East, no matter how the object is rotated. This is where the magic of quaternions comes in. If we multiply a local vector on the right by the object's rotation, it is converted into the needed world vector. So, what we need is CODE vector newPos = p + <1,0,0> * r; // right Alternative approach would be, there's functions in LSL which allow you directly extract local forward, up and left vectors from provided rotation. Such vector is 1 m long so in this particular example, the code would be simply: CODE vector newPos = p + llRot2Fwd( r );
RobbyRacoon Olmstead Red warrior is hungry! Join date: 20 Sep 2006 Posts: 1,821	12-17-2006 19:33 Sometimes you want to know if something is in front of you or, conversely, whether another object is facing you. It is easy enough to know whether you are facing some other point, and often a half-sphere sensor sweep is all you need for that, but what about when some other object or avatar is facing you? To use an example, consider that you are writing a swordfighting script and need to determine whether your opponent, who is blocking, is facing away from you. You might wish to know this so that your opponent cannot block attacks from behind. There are several other examples that come to mind quickly enough Below is some code that can determine either case (is it in front of me, or is it facing me) by turning a position and rotation into a plane equation and testing another position to see whether it is on the positive halfspace of that plane. Note that both cases are practically identical, just re-ordering the inputs in the equation. CODE integer isTargetInFrontOfMe( rotation myDir, vector myPos, vector targetPos ) { // Convert dir and pos to a plane equation vector p1 = myPos + <0,1,0> * myDir; vector p2 = myPos + <0,0,1> * myDir; vector normal = llVecNorm( (p2 - p1) % (myPos - p1) ); vector dv = llVecNorm( targetPos - p1 ); float test = normal * dv; return (test > 0); } integer isTargetFacingMe( vector myPos, vector targetPos, rotation targetDir ) { // Convert dir and pos to a plane equation vector p1 = targetPos + <0,1,0> * targetDir; vector p2 = targetPos + <0,0,1> * targetDir; vector normal = llVecNorm( (p2 - p1) % (targetPos - p1) ); vector dv = llVecNorm( myPos - p1 ); float test = normal * dv; return (test > 0); } default { touch_start(integer total_number) { llOwnerSay( "In front = " + (string)isTargetInFrontOfMe( llGetRot(), llGetPos(), llDetectedPos(0) ) ); llOwnerSay( "Facing me = " + (string)isTargetFacingMe( llGetPos(), llDetectedPos(0) , llDetectedRot(0) ) ); } } This is almost certainly not the most efficient method, but it is adequate for many purposes.
Joannah Cramer Registered User Join date: 12 Apr 2006 Posts: 1,539	12-17-2006 20:36 From: RobbyRacoon Olmstead CODE // Convert dir and pos to a plane equation vector p1 = myPos + <0,1,0> * myDir; vector p2 = myPos + <0,0,1> * myDir; vector normal = llVecNorm( (p2 - p1) % (myPos - p1) ); This bit can also be simplified to CODE vector normal = llRot2Fwd( myDir ); ^^
Lee Ponzu What Would Steve Do? Join date: 28 Jun 2006 Posts: 1,770	Your object is physical.... 12-17-2006 21:36 From: Vares Solvang I replaced the llLookAt line with your code, but I still don't rotate at all when the random impulse is applied. Does this kind of code only work if you are using if you are using llSetVel type code with it? Looking at your code, you can see that your object is physical. llSetRot() works on non-physical objects. Try using CODE llRotLookAt(r, f, d); f is how hard to push to make your object run (try 0.1 or 0.2) and d is how quickly the turning stops (try 1.0 or 2.0).
Lee Ponzu What Would Steve Do? Join date: 28 Jun 2006 Posts: 1,770	12-17-2006 21:51 From: RobbyRacoon Olmstead Sometimes you want to know if something is in front of you or, conversely, whether another object is facing you. CODE float test = normal * dv; return (test > 0); Can someone explain why test>0 translates to "in front of"? normal points forward, right? dv seems to point from about face level toward the other guy. So, what does normal*dv>0 mean?
RobbyRacoon Olmstead Red warrior is hungry! Join date: 20 Sep 2006 Posts: 1,821	12-18-2006 00:34 From: Joannah Cramer This bit can also be simplified to CODE vector normal = llRot2Fwd( myDir ); ^^ Neat! Thank you!
RobbyRacoon Olmstead Red warrior is hungry! Join date: 20 Sep 2006 Posts: 1,821	12-18-2006 09:47 From: Joannah Cramer This bit can also be simplified to CODE vector normal = llRot2Fwd( myDir ); ^^ So, using that change, the test becomes CODE integer isTargetFacingMe( vector myPos, vector targetPos, rotation targetDir ) { vector normal = llRot2Fwd( targetDir ); vector dv = llVecNorm( myPos - targetPos ); float test = normal * dv; return (test > 0); } I tried this, it seems to work wonderfully. I am quite pleased about the optimization, thank you.
Joannah Cramer Registered User Join date: 12 Apr 2006 Posts: 1,539	12-18-2006 11:10 From: Lee Ponzu Can someone explain why test>0 translates to "in front of"? normal points forward, right? dv seems to point from about face level toward the other guy. So, what does normaldv>0 mean? the vector vector part returns vector dot product, which is --if i recall right-- cosine of angle formed by these two vectors. This means as long as the returned value remains in (1, 0) range, the angle formed by vectors is less or equal 90 degree. When the value is in range (0, -1) this means the vectors are at angle greater than 90 degree which can be vaguely translated as being back to back with each other.
Seifert Surface Mathematician Join date: 14 Jun 2005 Posts: 912	12-18-2006 12:56 If a and b are vectors then a * b == llVecMag(a) * llVecMag(b) * llCos(the angle between a and b). If all you care about is the sign of the dot product, then it doesn't matter if the vectors are unit length or not. If you're after the angle itself via the cosine of it, then better throw in some llVecNorms here and there. _____________________ -Seifert Surface 2G!tGLf 2nLt9cG
Nuen Hyun Registered User Join date: 12 Apr 2007 Posts: 14	My Problem 04-21-2007 11:51 In the interest of learning more about LL, I decided to add a sit script to a simple seat. I thought it would be as simple as taking an existing sit script and modifying the rotation or sit orientation. The seat is a hollow cylinder rotated 90 degrees and cut till there is about 45'ish degrees left to sit on. Sitting on it with ZERO_ROTATION I appear to sit on the rotated cylinder (imagine the original rotated 90 degrees). I tried to do a simple rotation to get me back on the seat, but I am missing something. Perhaps an axis translation? Can anyone help clear things for me? Thank you.
Lee Ponzu What Would Steve Do? Join date: 28 Jun 2006 Posts: 1,770	more data needed 04-22-2007 09:09 ...but your logic seems right. Sit with ZERO_ROTATION, see how it looks, and then change the rotation in the llSetSitTarget() to adjust. Did you use radians or degrees?
Nuen Hyun Registered User Join date: 12 Apr 2007 Posts: 14	04-22-2007 11:37 I figured it out, or at least what works. Did more searching and found http://wiki.secondlife.com/wiki/Rotation to help. My mistake was, I left the 's' parameter of the rotation as 1.0 not knowing what to do with it. To fix, I used 'Euler2Rot ' and supplied only my rotations. With this, I got my Avitar to sit where I wanted him to.
Teddy Qinan Registered User Join date: 10 Mar 2007 Posts: 34	11-22-2007 15:37 How do I find the direction an object is facing flattened to the x or y axis? ie, if my object's rotation is rot, what compass direction is it facing? Edit: I originally wrote "flattened to the z-axis" but of course that wouldn't be flat.
Tyken Hightower Automagical Join date: 15 Feb 2006 Posts: 472	11-22-2007 18:13 From: Teddy Qinan How do I find the direction an object is facing flattened to the z-axis? ie, if my object's rotation is rot, what compass direction is it facing? vector direction = llRot2Fwd(llGetRot()); You can set direction.z to 0.0 and thus it will be 'flat.' _____________________
Void Singer Int vSelf = Sing(void); Join date: 24 Sep 2005 Posts: 6,973	11-22-2007 21:40 From: Teddy Qinan How do I find the direction an object is facing flattened to the x or y axis? ie, if my object's rotation is rot, what compass direction is it facing? Edit: I originally wrote "flattened to the z-axis" but of course that wouldn't be flat. by ignoring them list vListCompassPoints = ["W", "S", "E", "N", "W"]; vector vVecCompass = llRot2Euler( llGetRot() ) * RAD_TO_DEG; integer vIntPoint = vVecCompass.z / 90 + 2; string vStrFacing = llList2String( vListCompassPoints, vIntPoint ); the code can be simpler, but I think you get the idea... rot 2 euler returns values from - to + 180, to avoid inversions of other axis'... divide by the degrees between compass points for a range of options, shift the range into the usable format and select the matching option from a list... note since +/-180 is the same direction, you may need to have it in the list at both extremes, I can't remember is the equation prefers one or another, so expect both using the above mentioned rot2fwd you'd similarly discard the x and y elemnets, and only use the z... I think fwd for the purpose of that call is East (+X ), and you might need to reverse the list order.... _____________________ \| \| . "Cat-Like Typing Detected" \| . This post may contain errors in logic, spelling, and \| . grammar known to the SL populace to cause confusion \| \| - Please Use PHP tags when posting scripts/code, Thanks. \| - Can't See PHP or URL Tags Correctly? Check Out This Link... \| -
Teddy Qinan Registered User Join date: 10 Mar 2007 Posts: 34	11-22-2007 22:51 Thanks for the compass scripts, they do work well. Although I don't think I explained myself properly. I was meaning compass direction in degrees, and hoping for a combination of functions that would spit out a straight number and save me from having to use If statements to check for which quarter of the compass the prim was pointing. Maybe it can't be done?

Welcome to the Second Life Forums Archive

Quaternion rips and tricks