Math Is Fun Forum

ahhan .. ok ..

but Can you suggest me any method to verify the Code of each line segment?

thanks

Hi bob,

I wanna show one example.. and its directional code for 0 direction is not appropriate..

The example is shown in the attached image.

Hi all,

  ok As we have seen that angle is correct of all points.
Well the purpose of computing angle is to assign the 16 direction code for each line direction.

Since a circle circle is made up with 360 angles.
To get the 16 direction code for angles or direction of line, what we are doing is something like this ...

directionCode = ( angle / 22.5 ) - 16 , if angle is positive
else directionCode = (angle / 22.5) + 16, if angle is negative.

Since we need to get 16 direction Codes of angles.
so total angles 360 / 16 = 22.5 .

ok.. The problem i have with angle of Point B to C is that i got direction code 11, that meant the direction of line is downward. while the image attached in my post #6 shows that the line direction is from B to C that is upward direction .. therefore according to my figure in #6, direction code should 4 or 3.

A figure of direction code in circles are shown like this.

you can assign direction like this .. .

E = 0
between E and N, we have direction code 1 , 2 , 3
N = 4
between N to W, we have direction code 5 ,6 , 7
W = 8
between W to S, we have  direction Code 9, 10, 11
S = 12
between S to E , we have direction code 13, 14 , 15
and finally east = 16.

So, the angle from point B to C, gives me direction code 11.
which is wrong. because the line shows its direction to upward in my attached figure of post #6.

That'sy i am not satisfy with the angle of B to C. that's y, I am saying that my angle is inverted.

One more thing, that an image don't have negative x or y values. then how can i put the y values as negative to make the  angle of point B to C to the upward direction.

or i should change my method of angle computation?

Ahhhan.. Thanks .. hope to see you soon.

Actually, i am trying to find the direction of each line using angle computed by atan2 (dy, dx).

To find the direction of each line, i did something like this..

    if ( angleInDegree > 0 )
        directionCode = abs ((angleInDegree / 22.5) - 16 );
            print --> directionCode
   
        else
            directionCode = abs ((angleInDegree / 22.5) + 16);
            print --> directionCode
-------------------------------------------

My Result with angle and direction codes are like this

Original Points:
@ 0(105, 66)
@ 1(114, 92)
@ 2(104, 11)
@ 3(99, 131)
@ 4(71, 144)
@ 5(37, 168)

angle : 70.9065
angle : -97.0379
angle : 92.3859
angle : 155.095
angle : 144.782

Print the directional codes..
@ - 0:12
@ - 1:11
@ - 2:11
@ - 3:9
@ - 4:9

you guys can note the the angle of 1st index to the 2nd index point is -97 that meant in downward direction.

It should be at upward direction i meant angle should be arround 90.
and direction code should be 3 or 4.

Why my angle of point index 1 to index2, is inverted.

I calculated the angle by making a program in c++.

The peusdo code is something like this

for: i 1 to n-1  //n is the size of vector points

dx = points [i-1].x - points[i].x
dy = pointsp[i-1].y - points[i].y

angle = atan2 (dy , dx ) * 180/pi 

This is the way i am coding to compute the angle

Hi guys, thanks for replying.

Kindly see my points shown on image below, where the green and red circles are the start and end point and all other other intermediate points are in black circle.

I computed angle using atan2 (dy,dx),
Problem is that the direction from 1st index point to the 2nd index point is shown  vertically in the attached image. but my computed angle shows the direction in downward direction.

Computed angles are shown below..

Original Points:
@ 0(105, 66)
@ 1(114, 92)
@ 2(104, 11)
@ 3(99, 131)
@ 4(71, 144)
@ 5(37, 168)

angle : 70.9065
angle : -97.0379
angle : 92.3859
angle : 155.095
angle : 144.782

Why my angle vertical angle is inverted to downward direction using atan2(dy,dx) ?

Anyother method to normalize the datasets?

Thanks bob

yes, what i wanna do is.. if angel of segment ab is same as angle of bc
that meant points a ,b ,c are in the same direction.

then delete point b.. so we will consider line from point A to C.
so finally we should have a line AC with direction.

In other words we can say that point A , B , C are coplanar.

so to get the direction of segments, we need to get angle.

to get angle, i used this method

theta = acos ( (u.v) / |u| * |v| )

but this give angle of point with origin.

i don't need in that way.