c# - Velocity at an angle -

i'm trying find velocity @ angle.

to i'm trying use triangle, i'm running road blocks.

this code moves object

velocity = new vector3((float)math.cos(mathc.angletopoint(enemyobject.transform.position, playerposition)),               (float)math.sin(mathc.angletopoint(enemyobject.transform.position, playerposition)), 0); 

this angletopoint method

public static double angletopoint(vector3 startingpoint, vector3 endpoint) {     double hypotenuse = linelength(startingpoint, endpoint);     double adjacent = linelength(startingpoint, new vector3(endpoint.x, startingpoint.y, 0));     double opposite = linelength(endpoint,  new vector3(endpoint.x, startingpoint.y, 0));      double angle = adjacent / hypotenuse;       return math.acos(degreetoradian(angle));  } 

and linelength method

public static float linelength(vector2 point1, vector2 point2) {     return math.abs((float)math.sqrt(math.pow((point2.x - point1.x), 2)+math.pow((point2.y - point1.y),2)));  } 

i getting lot of nan errors, , movement not behave how want to.

edit : have solved problem. i'm not sure explained myself well, allow me attempt again. not physicist excuse me if of these terms wrong.

my goal have object move @ constant speed regardless of orientation. can assume person holding gun in direction north (0, 1) , rotate 45 degrees , fire gun. speed of gun scalar quantity, such 50 units per second. wanted know x , y values of vector needed have movement, in direction. velocity (0, 50) rotated 45 degrees right.

i know velocity.x = speedcos(angle) , velocity.y = speedsin(angle), needed find value of angle.

to this, line of thinking make right triangle based off starting position , destination, find angle using trig.

public static double angletopoint(vector3 startingpoint, vector3 endpoint) {     double hypotenuse = linelength(startingpoint, endpoint);     double adjacent = linelength(startingpoint, new vector3(endpoint.x, startingpoint.y, 0));     double opposite = linelength(endpoint,  new vector3(endpoint.x, startingpoint.y, 0));      double angle = adjacent / hypotenuse;       return math.acos(degreetoradian(angle));  } 

this code making right triangle. reason opposite there though it's not used because attempted multiple ways try accomplish this, kept encountering errors. after making right triangle, takes adj , hypo obtain cos(adj/hypo), call acos on give me angle in radians. didn't work however, did not return angle , created lot of nan errors.

after searching found thread , explanation of atan2

https://gamedev.stackexchange.com/questions/14602/what-are-atan-and-atan2-used-for-in-games

http://i.stack.imgur.com/xqiwg.png

this graph made me realize if translated line startingpoint, endpoint startingpoint = 0 call atan2 , returned desired angle. code accomplishes that.

public static double getangletopoint(vector3 startingpoint, vector3 endpoint) {     endpoint -= startingpoint;     return math.atan2(endpoint.y, endpoint.x); }  velocity = new vector3(speed * (float)math.cos(mathc.getangletopoint(startingposition, playerposition)),               speed * (float)math.sin(mathc.getangletopoint(startingposition, playerposition)), 0); 

is helpful : how calculate velocity @ angle ?

(sounds gaming development related question, might more here) https://gamedev.stackexchange.com/

(or maybe here too) https://math.stackexchange.com/