Unit 3: Overview of transformation - WordPress.com...UNIT 3: OVERVIEW OF TRANSFORMATION Two...

1 Course Coordinator: Mrs. Kshirsagar S.R. M.M.Polytechnic, Thergaon , Pune

UNIT 3: OVERVIEW OF TRANSFORMATION

Two dimensional transformation

In many applications, changes in orientations, size, and shape are accomplished with geometric

transformations that alter the coordinate descriptions of objects.

Basic geometric transformations are: These are most useful and most commonly used.

Translation (Position)

Rotation (Orientation) Scaling (Size)

Other transformations: These transformations are useful in certain applications.

Reflection (Mirror)

Shear (Size)

2D Translation

- Moves points to new locations by adding translation amounts to the coordinates of the

points.

• Initial Position point P (x, y)

• The new point P’ (x’, y’) Where,

x’ = x + tx

y’ = y + ty

tx and ty is the displacement in x and y respectively.

The translation pair (tx, ty) is called a translation vector or shift vector.

Matrix Representation

OR P’ = P + T

Program: Write a program for 2D Translation of a Triangle.

#include

#include

#include

#include

#include

int x1,y1,x2,y2,x3,y3,mx,my;

CO3 : Develop programs for 2D and 3D transformations

CO4 : Use projections to visualize objects on view plane



void draw();

void tri();

void main()

{

int gd=DETECT,gm; int c;

initgraph(&gd,&gm,"c:\\turboc3\\bgi ");

printf("Enter the 1st point for the triangle:");

scanf("%d%d",&x1,&y1);

printf("Enter the 2nd point for the triangle:");


printf("Enter the 3rd point for the triangle:");


cleardevice(); draw();

getch();

tri();

getch();

}

void draw()

{

line(x1,y1,x2,y2);

line(x2,y2,x3,y3);

line(x3,y3,x1,y1);

}

void tri()

{

int x,y,a1,a2,a3,b1,b2,b3;

printf("Enter the Transaction coordinates");

scanf("%d%d",&x,&y);

cleardevice();

a1=x1+x;

b1=y1+y;

a2=x2+x;

b2=y2+y;



a3=x3+x;

b3=y3+y;

line(a1,b1,a2,b2);

line(a2,b2,a3,b3);

line(a3,b3,a1,b1);

}

Rotation

Default rotation center: Origin (0,0)

Rotation is applied to an object by repositioning it along a circular path in the xy plane. To

generate a rotation, we specify

o Rotation angle θ

o Pivot point ( xr , yr)

Positive values of θ for counterclockwise rotation

Negative values of θ for clockwise rotation.

(x,y) ---> Rotate about the origin by θ" --->(x’, y’)

x = r cos (φ)

y = r sin (φ)

x’ = r cos (φ + θ)

y’ = r sin (φ + θ)

x’ = r cos (φ + θ)= r cos(φ) cos(θ) – r sin(φ) sin(θ)

= x cos(θ) – y sin(θ)

y’ = r sin (φ + θ) = r sin(φ) cos(θ) + r cos(φ)sin(θ)

= y cos(θ) + x sin(θ)

So, x’ = x cos(θ) – y sin(θ) and y’ = y cos(θ) + x sin(θ)

Representing the above equation in matrix form,

Where R is the rotation matrix

P’ = P. R



For positive rotation angle, we can use the above rotation matrix. However, for negative angle

rotation, the matrix will change as shown below –

Program: Write a program for 2D Rotation of a Triangle

#include

#include

#include

#include

#include

void triangle(int x1,int y1,int x2,int y2,int x3,int y3);

void Rotate(int x1,int y1,int x2,int y2,int x3,int y3);

void main()

{

int gd=DETECT,gm;

int x1,y1,x2,y2,x3,y3;

initgraph(&gd,&gm,"c:\\turboc3\\bgi");







triangle(x1,y1,x2,y2,x3,y3);

getch();

cleardevice();

Rotate(x1,y1,x2,y2,x3,y3);

setcolor(1);

triangle(x1,y1,x2,y2,x3,y3);

getch();

}

void triangle(int x1,int y1,int x2,int y2,int x3,int y3)

{



line(x1,y1,x2,y2);

line(x2,y2,x3,y3);

line(x3,y3,x1,y1);

}

void Rotate(int x1,int y1,int x2,int y2,int x3,int y3)

{

int x,y,a1,b1,a2,b2,a3,b3,p=x2,q=y2;

float Angle;

printf("Enter the angle for rotation:");

scanf("%f",&Angle);

cleardevice();

Angle=(Angle*3.14)/180;

a1=p+(x1-p)*cos(Angle)-(y1-q)*sin(Angle);

b1=q+(x1-p)*sin(Angle)+(y1-q)*cos(Angle);





printf("Rotate");

triangle(a1,b1,a2,b2,a3,b3);

}

Scaling:

To change the size of an object, scaling transformation is used. In the scaling process, you

either expand or compress the dimensions of the object.

Let us assume that the original coordinates are (X, Y), the scaling factors are (SX, SY), and the

produced coordinates are (X’, Y’).

This can be mathematically represented as shown below –

X' = X. SX and Y' = Y. SY

The scaling factor SX, SY scales the object in X and Y direction respectively. Scaling matrix

form as below –

OR

P’ = P. S

Where S is the scaling matrix. The scaling process is shown in the following figure.



If we provide values less than 1 to the scaling factor S, then we can reduce the size of the

object. If we provide values greater than 1, then we can increase the size of the object.

Program: Write a program for 2D Scaling of a Triangle

#include

#include

#include

#include

#include

int x1,y1,x2,y2,x3,y3,mx,my;

void draw();

void scale();

void main()

{

int gd=DETECT,gm;

int c;








draw();

scale();

}

void draw()

{

line(x1,y1,x2,y2);

line(x2,y2,x3,y3);

line(x3,y3,x1,y1);

}

void scale()



{

int x,y,a1,a2,a3,b1,b2,b3; int mx,my;

printf("Enter the scalling coordinates");


mx=(x1+x2+x3)/3;

my=(y1+y2+y3)/3;

cleardevice();

a1=mx+(x1-mx)*x;

b1=my+(y1-my)*y;

a2=mx+(x2-mx)*x;

b2=my+(y2-my)*y;

a3=mx+(x3-mx)*x;

b3=my+(y3-my)*y;

line(a1,b1,a2,b2);

line (a2,b2,a3,b3);

line(a3,b3,a1,b1);

draw();

getch();

}

Homogeneous coordinates: In design and picture formation process, many times require to perform translation, rotations

and scaling to fit the picture components into their proper positions.

General matrix form:

For Translation:

For Rotation:



For Scaling:

(To produce sequence of transformation with above equations, such as translation followed

by rotation and then scaling, the calculation of transformed coordinates one step at a time. To

combine sequence of transformations into one transformation so that final coordinate

positions are obtained directly from initial coordinates. This eliminates the calculation of

intermediate coordinate values.)

To perform a sequence of transformation such as translation followed by rotation and scaling,

we need to follow a sequential process −

• Translate the coordinates,

• Rotate the translated coordinates, and then

• Scale the rotated coordinates to complete the composite transformation.

To shorten this process, we have to use 3×3 transformation matrix instead of 2×2

transformation matrix. To convert a 2×2 matrix to 3×3 matrix, we have to add an extra

dummy coordinate W.

In this way, we can represent the point by 3 numbers instead of 2 numbers, which is called

Homogenous Coordinate system.

In this system, we can represent all the transformation equations in matrix multiplication.

Any Cartesian point P(X, Y) can be converted to homogenous coordinates by P’ (Xh, Yh, h).

Homogeneous coordinates for translation:

So



Homogeneous coordinates for Rotation:

So,

Homogeneous Coordinates for Scaling:

So,

Reflection:



Reflection is the mirror image of original object. In other words, we can say that it is a rotation

operation with 180°. In reflection transformation, the size of the object does not change. The

examples of some common reflections are:

Program: To Perform 2d Transformations (Reflection)

#include

#include

#include



#include

#include

void disp(int n,float c[][3])

{

float maxx,maxy;

int i;

maxx=getmaxx();

maxy=getmaxy();

maxx=maxx/2;

maxy=maxy/2;

i=0;

while(i



int i=0,ch,j;

cleardevice();

printf("\n\t* * MENU * *");

printf("\n\t1) ABOUT X-AXIS");

printf("\n\t2) ABOUT Y-AXIS");

printf("\n\t3) ABOUT ORIGIN");

printf("\n\t4) ABOUT Y=X");

printf("\n\t5) ABOUT Y=-X");

printf("\n\t6) EXIT”");

printf("\n\tENTER YOUR CHOICE :");

scanf("%d",&ch);

clrscr();

cleardevice();

disp(n,c);

for(i=0;i



b[1][1]=0;

b[0][1]=-1;

b[1][0]=-1;

break;

case 6:

break;

default:

printf("“\n\tINVALID CHOICE ! ");

break;

}

mul(n,b,c,a);

setcolor(RED);

disp(n,a);

}

void main()

{

int i,j,k,cho,n,gd=DETECT,gm;

float c[10][3],tx,ty,sx,sy,ra;


printf("\nEnter the number of vertices : ");

scanf("%d",&n);

for(i=0;i



X shear

The X-Shear preserves the Y coordinate and changes are made to X coordinates, which causes

the vertical lines to tilt right or left as shown in below figure.

The transformation matrix for X-Shear can be represented as –

Y Shear

The Y-Shear preserves the X coordinates and changes the Y coordinates which causes the horizontal

lines to transform into lines which slopes up or down as shown in the following figure



The Y-Shear can be represented in matrix from as –

Shearing relative to other reference line: In x shear transformation use y reference line and in y shear use x reference line. X shear with

y reference line:

y shear with x reference line:

Program: Shearing transformation in C graphics

#include

#include

#include

#include

#include

void mul(int mat[3][3],int vertex[10][3],int n);

void shear(int vertex[10][3],int n);

void init(int vertex[10][3],int n);

int main()

{

int i,x,y,xsh,ysh,xref,yref;



int vertex[10][3],n; clrscr();

printf("\nEnter the no. of vertex : ");

scanf("%d",&n);

for(i=0;i



for(i=0;i



shear_array[0][2]=0;



init(vertex,n);

mul(shear_array,vertex,n);

break;

case 2:

printf("\nEnter the y shear : ");

scanf("%d",&ysh);




shear_array[0][1]=ysh;






init(vertex,n);


break;

case 3:

printf("\nEnter the y shear : ");

scanf("%d",&ysh);

printf("\nEnter the x ref : ");

scanf("%d",&xref);




shear_array[0][1]=ysh;


shear_array[2][1]=-ysh*xref;




init(vertex,n);


break;

case 4:

printf("\nEnter the x shear : ");



scanf("%d",&xsh);

printf("\nEnter the y ref: ");

scanf("%d",&yref);


shear_array[1][0]=xsh;

shear_array[2][0]=-xsh*yref;







init(vertex,n);


break;

}

printf("\n Do you want to continue");

ans=getche();

}

while(ans=='y'||ans=='Y');

}

Composite transformations

The basic purpose of composing transformations is to gain efficiency by applying a single

composed transformation to a point, rather than applying a series of transformation, one after

another.

If a transformation of the plane T1 is followed by a second plane transformation T2, then the

result itself may be represented by a single transformation T which is the composition of T1

and T2 taken in that order. This is written as T = T1∙T2.

For example, to rotate an object about an arbitrary point (Xp, Yp), we have to carry out three

steps – (T*R*T)

• Translate point (Xp, Yp) to the origin.

• Rotate it about the origin.

• Finally, translate the center of rotation back where it belonged.



Rotation about arbitrary point:

Suppose the reference point of rotation is other than origin, then in that case follow series of

transformation.

Assume that to rotate a point P1 with respect to (Xm, Ym) then perform three steps.

I) Translation: First we have to translate the (Xm, Ym) to origin as shown in figure Translation matrix (T1) will become



3D Transformation:

3D Translation:

Three dimensional transformation matrix for translation with homogeneous coordinates is

given below. It specifies three coordinates with their own translation factor.

T=[

1 0 0 00 1 0 00 0 1 0𝑡𝑥 𝑡𝑦 𝑡𝑧 1

]

P’= P. T

[𝑥′ 𝑦′ 𝑧′ 1] = [𝑥 𝑦 𝑧 1] * [

1 0 0 00 1 0 00 0 1 0𝑡𝑥 𝑡𝑦 𝑡𝑧 1

]

= [𝑥 + 𝑡𝑥 𝑦 + 𝑡𝑦 𝑧 + 𝑡𝑧 1]

3D Scaling:

Three dimensional transformation matrix for scaling with homogeneous coordinates is given

below. It specifies three coordinates with their own scaling factor.



3D Rotation:

Three dimensional transformation matrix for rotation with homogeneous coordinates is given

below. It specifies three coordinates with their own rotation factor.



Program for 3D Translation

#include

#include

#include

#include

#include

int x1,x2,y1,y2,mx,my,depth;

void draw();

void trans();

void main()

{

int gd=DETECT,gm,c;

initgraph(&gd,&gm,"C:\\TurboC3\\BGI");

printf("\n\t\t3D Translation\n\n");

printf("\nEnter 1st top value(x1,y1):");


printf("Enter right bottom value(x2,y2):");


depth=(x2-x1)/4;

mx=(x1+x2)/2;

my=(y1+y2)/2;

draw();

getch();

cleardevice();

trans();

getch();



}

void draw()

{

bar3d(x1,y1,x2,y2,depth,1);

}

void trans()

{

int a1,a2,b1,b2,dep,x,y;

printf("\n Enter the Translation Distances:");


a1=x1+x;

a2=x2+x;

b1=y1+y;

b2=y2+y;

dep=(a2-a1)/4;

bar3d(a1,b1,a2,b2,dep,1);

setcolor(5);

draw();

}

Program for 3D Scaling

#include

#include

#include

#include

#include

int x1,x2,y1,y2,mx,my,depth;

void draw();

void scale();

void main()

{

int gd=DETECT,gm,c;

initgraph(&gd,&gm,"C:\\TurboC3\\BGI");

printf("\n\t\t3D Scaling\n\n");

printf("\nEnter 1st top value(x1,y1):");


printf("Enter right bottom value(x2,y2):");


depth=(x2-x1)/4;

mx=(x1+x2)/2;



my=(y1+y2)/2;

draw();

getch();

cleardevice();

scale();

getch();

}

void draw()

{

bar3d(x1,y1,x2,y2,depth,1);

}

void scale()

{

int x,y,a1,a2,b1,b2,dep;

printf("\n\n Enter scaling Factors:");


a1=mx+(x1-mx)*x;

a2=mx+(x2-mx)*x;

b1=my+(y1-my)*y;

b2=my+(y2-my)*y;

dep=(a2-a1)/4;

bar3d(a1,b1,a2,b2,dep,1);

setcolor(5);

draw();

}

Program for 3D Rotation

#include

#include

#include

#include

int maxx,maxy,midx,midy;

void axis()

{

getch();

cleardevice();

line(midx,0,midx,maxy);

line(0,midy,maxx,midy);

}

void main()



{

int x,y,z,o,x1,x2,y1,y2;

int gd=DETECT,gm;

detectgraph(&gd,&gm);


maxx=getmaxx();

maxy=getmaxy();

midx=maxx/2;

midy=maxy/2;

axis();

bar3d(midx+50,midy-100,midx+60,midy-90,5,1);

printf("Enter rotating angle");

scanf("%d",&o);

x1=50*cos(o*3.14/180)-100*sin(o*3.14/180);

y1=50*sin(o*3.14/180)+100*cos(o*3.14/180);

x2=60*cos(o*3.14/180)-90*sin(o*3.14/180);

y2=60*sin(o*3.14/180)+90*cos(o*3.14/180);

axis();

printf("After rotation about z axis");

bar3d(midx+x1,midy-y1,midx+x2,midy-y2,5,1);

axis();

printf("After rotation about x axis");

bar3d(midx+50,midy-x1,midx+60,midy-x2,5,1);

axis();

printf("After rotation about yaxis");

bar3d(midx+x1,midy-100,midx+x2,midy-90,5,1);

getch();

closegraph();

}

Types of projections

• It is the process of converting a 3D object into a 2D object. • It is also defined as mapping or transformation of the object in projection plane or

view plane.

• Types of projection – Parallel Projection – Perspective Projection

Parallel Projection

• Parallel projection discards z-coordinate and parallel lines from each vertex on the object are extended until they intersect the view plane.

• In parallel projection, we specify a direction of projection instead of center of projection.



• In parallel projection, the distance from the center of projection to project plane is infinite.

• In this type of projection, we connect the projected vertices by line segments which correspond to connections on the original object.

• Parallel projections are less realistic, but they are good for exact measurements. • In this type of projections, parallel lines remain parallel and angles are not preserved. • Various types of parallel projections are shown in the following hierarchy.

Orthographic Projection

• In orthographic projection the direction of projection is normal to the projection of the plane.



• There are three types of orthographic projections − – Front Projection – Top Projection – Side Projection

Oblique Projection • In orthographic projection, the direction of projection is not normal to the projection

of plane.

• In oblique projection, we can view the object better than orthographic projection. • There are two types of oblique projections − Cavalier and Cabinet. • The Cavalier projection makes 45° angle with the projection plane. • The projection of a line perpendicular to the view plane has the same length as the

line itself in Cavalier projection.

• In a cavalier projection, the foreshortening factors for all three principal directions are equal.

• The Cabinet projection makes 63.4° angle with the projection plane. • In Cabinet projection, lines perpendicular to the viewing surface are projected at ½

their actual length.

• Both the projections are shown in the following figure –

Perspective Projection

• In perspective projection, the distance from the center of projection to project plane is finite and the size of the object varies inversely with distance which looks more

realistic.

• The distance and angles are not preserved and parallel lines do not remain parallel. • Instead, they all converge at a single point called center of projection or projection



reference point.

There are 3 types of perspective projections which are shown in the following chart.

• One point perspective projection is simple to draw.

• Two point perspective projection gives better impression of depth.

• Three point perspective projection is most difficult to draw.



• Perspective projection is located as a finite point whereas Parallel projection is located at infinite points.

• Perspective projection form a realistic picture of object whereas Parallel projection do not form realistic view of object.

• Perspective projection cannot preserve the relative proportion of an object whereas Parallel projection can preserve the relative proportion of an object.

• Projector in perspective projection is not parallel whereas Projector in parallel projection is parallel.

• Perspective projection represents the object in three dimensional way whereas Parallel projection represents the object in a different way like telescope.

• The lines of perspective projection are not parallel whereas The lines of parallel projection are parallel.

• Perspective projection cannot give the accurate view of object whereas Parallel projection can give the accurate view of object.

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