Hello, iam using gluUnproject () function to retrieve the object coordinates from the screen coordinates. when i click on a point (2,2,2) i get the output from the function as(2.218335,2.226619,-0.000000) when i click on a point (3,3,3) i get the output as (2.218335,2.226619,-0.000000) when i click on a point (4,4,4) i get the output as (3.079899,3.084041,-0.000000) when i click on a point (5,5,5) i get the output as (3.079899,3.084041,-0.000000) why is there such a discrepancy in the actual values and the returned values of the function?? is it the nature of the function itself or there is some other problem with my code?? i want to retrieve atleast the x-coordinate more or less exactly?? plz help me ,may be with any other possible solution. thanking you, vamsee. the code is as follows: #include <GL/glut.h> #include <stdlib.h> #include <stdio.h> void display (void) { glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glLoadIdentity(); // glu.gluLookAt(1.0,1.0,1.0,0.0,0.0,0.0,0.0,0.0,0.0); // glu.gluLookAt(0.0,0.5,0,0,0.0,0.05,0,0,1); glOrtho(0.0, 5.0, 0.0, 5.0, 0.0, 5.0); //glTranslatef(-5.0f, 0.0f, 0.0f); // gl.glRotatef(rtri,0,6.0f,0); // glu.gluLookAt(camerax, cameray, cameraz, 0, 0.0, 0.05, 0, 1, 1); glPointSize(5); // for (i = 0, j = i + 1; i < array11.size() - 1; i++, j++) // { // if (arraya1[j] == arraya1 + 1) // { glBegin(GL_POINTS); glVertex3d(1,1,1); glVertex3d(2,2,2); glVertex3d(3,3,3); glVertex3d(4,4,4); glVertex3d(5,5,5); glEnd(); // } // } glFlush(); } void reshape(int w, int h) { glViewport(0,0,(GLsizei) w ,(GLsizei) h); glMatrixMode(GL_PROJECTION); glLoadIdentity(); gluPerspective(45.0,(GLfloat) w / (GLfloat) h,1.0,100.0); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); } void mouse (int button,int state,int x,int y) { GLint viewport[4]; GLdouble mvmatrix[16],projmatrix[16]; GLint realy; GLdouble wx,wy,wz; int returnvalue1=0,returnvalue2=0; // glLoadIdentity(); switch (button) { case GLUT_LEFT_BUTTON: if( state ==GLUT_DOWN) { glGetIntegerv(GL_VIEWPORT,viewport); glGetDoublev(GL_MODELVIEW_MATRIX,mvmatrix); glGetDoublev(GL_PROJECTION_MATRIX,projmatrix); realy = viewport[3]- (GLint) y -1; printf("Coordinates at cursor are (%4d,%4d) \n ",x ,realy); returnvalue1 = gluUnProject((GLdouble) x,(GLdouble) realy,0.0,mvmatrix,projmatrix,viewport,&wx,&wy,&wz); printf("returnvalue1 is %d \n",returnvalue1); printf("World coords at z= 0.0 are (%f,%f,%f) \n",wx,wy,wz); returnvalue2 = gluUnProject((GLdouble) x,(GLdouble) realy,1.0,mvmatrix,projmatrix,viewport,&wx,&wy,&wz); printf("return value2 is %d \n",returnvalue2); printf("World coords at z= 1.0 are (%f,%f,%f) \n",wx,wy,wz); } break; case GLUT_RIGHT_BUTTON: if (state == GLUT_DOWN) exit(0); break; default: break; } } int main(int argc , char** argv) { glutInit(&argc,argv); glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB ); glutInitWindowSize(500,500); glutInitWindowPosition(100,100); glutCreateWindow(argv[0]); glutDisplayFunc(display); glutReshapeFunc(reshape); glutMouseFunc(mouse); glutMainLoop(); return 0; }