Demonstration and Measurement of Spatial Jitter

Before trying this example, if you have not installed a VRML viewer then please go to these instructions.

To see a demostration of position jitter, after loading the example vrml file, follow this procedure:

after the file is loaded move around a little by left clicking in the 3D area and dragging the mouse. This is so you cansee what motion is like at the origin. In some cases, e.g. when the web browser is IE, you have to left click in the window once beforehand.
please select successive viewpoints using the Page Down key or right click and choos the viewpoint.

The Figure below shows the test model which was designed in VRML using a simple arrangement of viewpoints and coloured dots. Each dot was given a different colour so they could be identified when they moved relative to each other due to jitter. The viewpoint was initially positioned at (1,1,1) and oriented to look at the origin. This gave a viewpoint that was not aligned to any axis thus ensuring there would be a spatial error contribution from each axis variable to the viewpoint position. The dots were positioned irregularly but sufficiently far from the screen edges that they were unlikely to jitter out of view and thus be unobservable. The dots were not placed on world coordinate axes to maximise the spatial error contribution from their coordinates.The dots were also positioned away from the \emph{screen} coordinate axes for the same reason. Furthermore the dots were arranged on a plane perpendicular to the view vector making them close to equidistant from the observer and consequently with similar perspective foreshortening and therefore have relatively comparable displacements.

The Figure shows a screen snapshot of the model centered at the origin. This was used as the reference image to compare corresponding coloured dot positions in other images. Once the test model was setup, a series of images were recorded with the scene (including viewpoint) displaced at increasing distances from the origin. The results may be found in the thesis.