1 00:00:00,060 --> 00:00:02,430 The following content is provided under a Creative 2 00:00:02,430 --> 00:00:03,820 Commons license. 3 00:00:03,820 --> 00:00:06,030 Your support will help MIT OpenCourseWare 4 00:00:06,030 --> 00:00:10,120 continue to offer high quality educational resources for free. 5 00:00:10,120 --> 00:00:12,660 To make a donation or to view additional materials 6 00:00:12,660 --> 00:00:16,620 from hundreds of MIT courses, visit MIT OpenCourseWare 7 00:00:16,620 --> 00:00:19,700 at ocw.mit.edu. 8 00:00:19,700 --> 00:00:21,450 PROFESSOR: --is that for objects that 9 00:00:21,450 --> 00:00:24,030 look the same size in the camera, 10 00:00:24,030 --> 00:00:26,910 the angle between a line of sight 11 00:00:26,910 --> 00:00:30,900 along one edge of the object and a line of sight 12 00:00:30,900 --> 00:00:33,450 along the other edge of the object 13 00:00:33,450 --> 00:00:35,040 is always the same angle. 14 00:00:37,780 --> 00:00:40,440 [INAUDIBLE],, could you grab me one of those big kick balls? 15 00:00:44,040 --> 00:00:51,360 This is useful, because if we know that things in the camera 16 00:00:51,360 --> 00:00:54,660 look the same size they're always the same angle, that 17 00:00:54,660 --> 00:00:56,250 allows us, like you guys just did, 18 00:00:56,250 --> 00:00:59,190 to predict where we'd need to put this in order 19 00:00:59,190 --> 00:01:01,290 for it to look the same size. 20 00:01:01,290 --> 00:01:05,370 All we have to do is extend these lines out a little bit 21 00:01:05,370 --> 00:01:08,040 until the width between the lines 22 00:01:08,040 --> 00:01:11,610 gets to be large enough to accommodate the object. 23 00:01:11,610 --> 00:01:14,880 If you stand on your tiptoes and look if I put the object there, 24 00:01:14,880 --> 00:01:16,980 well, obviously the edges of the object 25 00:01:16,980 --> 00:01:18,510 are outside of my lines of sight. 26 00:01:18,510 --> 00:01:19,009 Whoops. 27 00:01:19,009 --> 00:01:22,470 Uh-oh, could you pull that back? 28 00:01:22,470 --> 00:01:25,290 Whereas if I go further back to right 29 00:01:25,290 --> 00:01:30,920 about here, if I extend this line of sight that way 30 00:01:30,920 --> 00:01:36,240 and if I extend that line of sight there, right about here 31 00:01:36,240 --> 00:01:39,750 the line of sight is going to be about the same angle 32 00:01:39,750 --> 00:01:42,190 for this object. 33 00:01:42,190 --> 00:01:45,780 So this is why astronomers and people who do image science 34 00:01:45,780 --> 00:01:50,910 call this thing, this width of the object in the image, 35 00:01:50,910 --> 00:01:56,570 they actually call it the angular width. 36 00:01:59,130 --> 00:02:02,130 It's the angular width, because it's the angle 37 00:02:02,130 --> 00:02:05,130 that the object takes up. 38 00:02:05,130 --> 00:02:07,140 If we had a different object that was larger, 39 00:02:07,140 --> 00:02:11,370 it would have a different angular width. 40 00:02:11,370 --> 00:02:15,421 So we have this idea of, in our case, 41 00:02:15,421 --> 00:02:16,920 we're not going to call it the width 42 00:02:16,920 --> 00:02:18,480 of the object in the image anymore, 43 00:02:18,480 --> 00:02:20,090 although that's what it is. 44 00:02:20,090 --> 00:02:24,090 But we're going to call it the angular width, because we're 45 00:02:24,090 --> 00:02:28,104 really not measuring a distance, we're measuring an angle. 46 00:02:28,104 --> 00:02:29,520 Because if we measured a distance, 47 00:02:29,520 --> 00:02:31,145 we'd actually measure the width of this 48 00:02:31,145 --> 00:02:35,240 and we'd come up with this column.