Question: Current images are taken at every 10.98 ft. Based on the results, can we suggest that the maximun spacing of taking images (e.g. 20 ft)?
I guess your question in other words whether our system can recognize the traffic sign as far as 20 fts away. However the image size in width and height that we can extract from the image depends on the various camera parameters. We do not have such information now to do the camera calibration to compute the expected pixel size of the traffic sign. And so the answer can not be made deterministically but intuitively from the samples we have. Let us set the current data set that we have been collecting manually. The minimum size that my last experiment (09/22/2006) correctly recognize is: 33x35 pixels for W1-1, 34x32 pixels for W1-2, 14x17 pixels for W1-8.
Sure above sizes are the minimum size of extracted sign images that Ibrahima identifies by hands. Let us see the actual image that the traffic signs are taken from. Though we do not have enough information to reinverse the correct distance from the camera on top of the moving car to the sign object, we may be able to guess the distance and say 20 fts are enough to reconize the specific type of traffic sign or not with the strong assumptions on its capturing contexts like lighting condition, camera focus, and occlusion-free condition.