## RE: [Algorithms] Projection

 RE: [Algorithms] Projection From: Tom Forsyth - 2000-11-30 13:39:14 ```The image gets bigger on screen, but if your eyes are aimed at the centre of the screen, that part of the screen is smaller in your vision. So in your vision, the size of the object does not change. It all works out in the end. You can use some sort of fisheye lens, which makes objects stay the same size (roughly), but it looks very very wrong. If you base your size on the Z-distance from the camera, not the sqrt(x^2+y^2+z^2) distance, it all works. A line of objects all at the same Z-distance are all the same size on-screen. However, as you rotate the camera, their Z-distance changes, even though their linear distance doesn't, which is why they change size. Tom Forsyth - purely hypothetical Muckyfoot bloke. This email is the product of your deranged imagination, and does not in any way imply existence of the author. > -----Original Message----- > From: Joe Ante [mailto:Joe@...] > Sent: 30 November 2000 09:26 > To: gdalgorithms-list@... > Subject: [Algorithms] Projection > > > Hi, > > For my texture LOD I am calculating the areas of the > projected bounding > boxes or if i want the exact value the actual geometry. > > Now what I have noted is that the more an objects moves away > from the center > of the screen, the bigger its screenspace becomes. (For > example if you simpy > rotate the camera) > Now I dont really believe that this happens in reality as > well. At least I > have always thought that if I move my head or eyes the > objects i see dont > become larger. > Is there actually a way to get rid of effect? (using a 4x4Matrix) > > And if not, does anyone have a good method to calculate the > screenspacearea > of an object in a way that the rotation of the camera has no > effect on the > screenspace area. If possible it should give me back the area > in screenspace > of the object if the camera directly faced the object (the > object is in the > center of the screen) > > bye joe > > _______________________________________________ > GDAlgorithms-list mailing list > GDAlgorithms-list@... > http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list > ```

 RE: [Algorithms] Projection From: Tom Forsyth - 2000-11-30 13:39:14 ```The image gets bigger on screen, but if your eyes are aimed at the centre of the screen, that part of the screen is smaller in your vision. So in your vision, the size of the object does not change. It all works out in the end. You can use some sort of fisheye lens, which makes objects stay the same size (roughly), but it looks very very wrong. If you base your size on the Z-distance from the camera, not the sqrt(x^2+y^2+z^2) distance, it all works. A line of objects all at the same Z-distance are all the same size on-screen. However, as you rotate the camera, their Z-distance changes, even though their linear distance doesn't, which is why they change size. Tom Forsyth - purely hypothetical Muckyfoot bloke. This email is the product of your deranged imagination, and does not in any way imply existence of the author. > -----Original Message----- > From: Joe Ante [mailto:Joe@...] > Sent: 30 November 2000 09:26 > To: gdalgorithms-list@... > Subject: [Algorithms] Projection > > > Hi, > > For my texture LOD I am calculating the areas of the > projected bounding > boxes or if i want the exact value the actual geometry. > > Now what I have noted is that the more an objects moves away > from the center > of the screen, the bigger its screenspace becomes. (For > example if you simpy > rotate the camera) > Now I dont really believe that this happens in reality as > well. At least I > have always thought that if I move my head or eyes the > objects i see dont > become larger. > Is there actually a way to get rid of effect? (using a 4x4Matrix) > > And if not, does anyone have a good method to calculate the > screenspacearea > of an object in a way that the rotation of the camera has no > effect on the > screenspace area. If possible it should give me back the area > in screenspace > of the object if the camera directly faced the object (the > object is in the > center of the screen) > > bye joe > > _______________________________________________ > GDAlgorithms-list mailing list > GDAlgorithms-list@... > http://lists.sourceforge.net/mailman/listinfo/gdalgorithms-list > ```