Hi buddies, I am trying to map a convex quadrilateral to a concave quadrilateral in 2D plane, or vice visa. Is the projective transformation a right mapping? If not, is there any transformation good for that? Thanks, Yong Hu

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- 1. OT: 3D - data import/export lib

Hi, it might be a little bit OT here, but i think here the profis to handle this. Im searching for a lib/ocx/... to import/export 3D-data (meshes/polygons). The import should handle minimum: - 3DS - DXF/DWG - .... Does anyone know such a produkt ? Thanks, Howie - 2. How to draw a smooth hill from a set of contours

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Hello everybody I have a scene with a simple perfect black box, and behind it a very very bright background. I took 100 samples, and just on that pixel, 50% of samples hit the light, and the rest, the black box. The bright area has an intensity of 10000, and the black box has an intensity of 0. 10000 * 50 + 0 * 50 = 50000 / 100 samples = 500 average pixel intensity The next pixel is 100% covered by the black box, so, the pixel is pure black. Now I store the result picture on a rectangular buffer. I loose all the sampling information. After all the rendering is done, I apply a simple tonemapping algorithm to the whole picture, for example, clamping all the values outside the 0..1 range. Now I display the image, and I get a complete aliased black box with a white background. How can I deal with this situation? In which part of the render pipeline should I apply an antialias algorithm?

Hi buddies, I am trying to map a convex quadrilateral to a concave quadrilateral in 2D plane, or vice visa. Is the projective transformation a right mapping? If not, is there any transformation good for that? Thanks, Yong Hu

Yong Hu schrieb: Projective transformation maps convex shapes to convex shapes, so it is the wrong mapping. You can (bijectively) map the vertices and then make an interpolation, I guess. However, I'd have to look up the details myself (it was long ago when I learned that). If I remember well the keyword was something like "tensor product face"? Norbert

Norbert_Paul schrieb: OOPS! Just realized, that then the interior of the convex shape spills over to the exterior of the concave shape. Maybe try triangulation.

1.mapping quadrilateral to quadrilateral

Hi buddies, I am trying to map a convex quadrilateral to a concave quadrilateral in 2D plane, or vice visa. Is the projective transformation a right mapping? If not, is there any transformation good for that? Thanks, Yong Hu

2.overlapping quadrilaterals: culling question

Hello, Could someone be so kind to tell me how come the green rectangle is drawn above the red rectangle when in fact it is located below? I think this has to do with some culling option I need to enable, but I'm not sure how. Basically, if I draw the green rectangle first then the pictures appears OK, but I need the drawing to be independent of how I view it with the camera so I cannot rely on drawing one quadrilateral or the other one first. Can anyone please let me know how to fix this problem? Thanks, Neil #include <GL/glut.h> void drawCube(void) { glClear(GL_COLOR_BUFFER_BIT); glMatrixMode(GL_MODELVIEW); glLoadIdentity(); glBegin(GL_QUADS); /* outer top face (red) */ glColor3f(1.0f, 0.0f, 0.0f); glNormal3f(0.0f, 1.0f, 0.0f); glVertex3f(0.0f, 1.0f, 0.0f); glVertex3f(1.0f, 1.0f, 0.0f); glVertex3f(1.0f, 1.0f, 1.0f); glVertex3f(0.0f, 1.0f, 1.0f); /* outer bottom face (green) */ glColor3f(0.0f, 1.0f, 0.0f); glNormal3f(0.0f, -1.0f, 0.0f); glVertex3f(0.0f, 0.0f, 0.0f); glVertex3f(1.0f, 0.0f, 0.0f); glVertex3f(1.0f, 0.0f, 1.0f); glVertex3f(0.0f, 0.0f, 1.0f); glEnd(); glutSwapBuffers(); glFlush(); } void idle(void) { drawCube(); } int main(int argc, char **argv) { glutInit(&argc, argv); glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE); glutInitWindowPosition(120, 80); glutInitWindowSize(640, 480); glutIdleFunc(idle); glutCreateWindow("hello"); glMatrixMode(GL_PROJECTION); glLoadIdentity(); gluPerspective(45.0, 1.0, 0.0, 3.0); gluLookAt(-1.0, 3.0, -1.0, 0.0, 1.0, 0.0, 0.0, 1.0, 0.0); glutMainLoop(); return 0; }

3.transform between convex and concave quadrilaterals

4.testing whether a point is contained in a quadrilateral

Hi Everyone- In 2D or 3D, I'm trying to write a quick algorithm to test if a point is contatined in a quadrilateral. I've come up with a couple of ideas, but both of them seem needlessly complex. Does anyone know of a quick way to do this? Or maybe you know of a resource I should check out. Thanks in advance. -spencer

5.Forming An Equilateral Triangle About The Centre Of A Planar Quadrilateral

Given a planar quadrilateral, I want to form a equilateral triangle about the centre of the quadrilateral, such that this triangle is of maximum size while still being equilateral and completely within the area defined by the quadrilateral. Any thoughts on the best way of calculating such a triangle? Adam

6. Fitting a quadrilateral to pixels

7. Smallest 4-sided polygon surrounding convex hull ( smallest convex quadrilateral)

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