Star tracker and lidar based night-time planetary navigation

Planetary navigation on planets with no global positioning infrastructure is a challenge which has been overcome in the past by using day-light dependent sensors. This thesis develops a platform to test a star tracker and LIDAR based night-time navigation system. Testing of the system confirmed its feasibility despite not meeting target performance. Global position was acquired to within five kilometres using the star tracker and refined to within 23% of true motion for a 13 m path using the LIDAR.

Star tracker and lidar based night-time planetary navigation

Planetary navigation on planets with no global positioning infrastructure is a challenge which has been overcome in the past by using day-light dependent sensors. This thesis develops a platform to test a star tracker and LIDAR based night-time navigation system. Testing of the system confirmed its feasibility despite not meeting target performance. Global position was acquired to within five kilometres using the star tracker and refined to within 23% of true motion for a 13 m path using the LIDAR.

Precise positioning is known as a loxodrome on a trajectory on navigation measurements with intense noise

The article proposes a method of improving the accuracy of determining the current coordinates of a moving object moving along a loxodromic trajectory by analytical three-dimensional projection of its coordinates determined by navigation measurements in conditions of intense interference on the trajectory of its true motion. The results of testing the efficiency of the proposed method, which was carried out by numerical simulation of the algorithms described in the work of determining the coordinates of the object on the loxodromic trajectory on noisy navigation measurements. The results indicates the possibility of effective use of the proposed approach. Keywords: analytical three-dimensional projection coordinates, geographic information systems, interference, known as a loxodrome path, navigation measurement.

The Anomalous Sun

Four clockwork-driven planetary automata built to show the true motion of the planets according to Ptolemaic theory, not just their mean motion, survive from the sixteenth century: one each in Paris, Vienna, Kassel, and Dresden. Close, on-site examination of their mechanisms by a team of historians of science and clockmakers has gone beyond existing accounts and revealed that, though they share a common aim, the machines differ fundamentally in their realization of even the “simplest” of the planetary motions, namely that of the Sun. Indeed, three different ways have been detected for producing the solar anomaly, the Sun’s non-uniform motion along the ecliptic in the course of a year. The oldest of the surviving machines (Paris) uses the uniform motion of an eccentric gear, another (Vienna) adapts what would be a geometrically equivalent epicycle, and the two other machines (Kassel and Dresden) make use of a centered gear with non-uniformly spaced teeth. This paper discusses these findings in detail. It argues that such differing approaches not only reflect varying degrees of collaboration among the actors involved in the construction of these four technical masterpieces – princely commissioners, learned astronomers, and artful craftsmen (with these categories sometimes overlapping) – but also that they offer a further, mechanical contribution to the centuries-old reception and refinement of Ptolemaic planetary theory.

The direction after-effect is a global motion phenomenon

Prior experience influences visual perception. For example, extended viewing of a moving stimulus results in the misperception of a subsequent stimulus's motion direction—the direction after-effect (DAE). There has been an ongoing debate regarding the locus of the neural mechanisms underlying the DAE. We know the mechanisms are cortical, but there is uncertainty about where in the visual cortex they are located—at relatively early local motion processing stages, or at later global motion stages. We used a unikinetic plaid as an adapting stimulus, then measured the DAE experienced with a drifting random dot test stimulus. A unikinetic plaid comprises a static grating superimposed on a drifting grating of a different orientation. Observers cannot see the true motion direction of the moving component; instead they see pattern motion running parallel to the static component. The pattern motion of unikinetic plaids is encoded at the global processing level—specifically, in cortical areas MT and MST—and the local motion component is encoded earlier. We measured the direction after-effect as a function of the plaid's local and pattern motion directions. The DAE was induced by the plaid's pattern motion, but not by its component motion. This points to the neural mechanisms underlying the DAE being located at the global motion processing level, and no earlier than area MT.

Newton’s Scholium on Time, Space, Place and Motion

In the Scholium to the Definitions at the beginning of the Principia, Newton distinguishes absolute time, space, place, and motion from their relative counterparts. He argues that they are indeed ontologically distinct, in that the absolute quantity cannot be reduced to some particular category of the relative, as Descartes had attempted by defining absolute motion to be relative motion with respect to immediately ambient bodies. Newton’s rotating bucket experiment, rather than attempting to show that absolute motion exists, is one of five arguments from the properties, causes, and effects of motion. These arguments attempt to show that no such program can succeed, and thus that true motion can be adequately analyzed only by invoking immovable places, that is, the parts of absolute space.

Aging and the Visual Perception of Motion Direction: Solving the Aperture Problem

An experiment required younger and older adults to estimate coherent visual motion direction from multiple motion signals, where each motion signal was locally ambiguous with respect to the true direction of pattern motion. Thus, accurate performance required the successful integration of motion signals across space (i.e., accurate performance required solution of the aperture problem) . The observers viewed arrays of either 64 or 9 moving line segments; because these lines moved behind apertures, their individual local motions were ambiguous with respect to direction (i.e., were subject to the aperture problem). Following 2.4 seconds of pattern motion on each trial (true motion directions ranged over the entire range of 360° in the fronto-parallel plane), the observers estimated the coherent direction of motion. There was an effect of direction, such that cardinal directions of pattern motion were judged with less error than oblique directions. In addition, a large effect of aging occurred—The average absolute errors of the older observers were 46% and 30.4% higher in magnitude than those exhibited by the younger observers for the 64 and 9 aperture conditions, respectively. Finally, the observers’ precision markedly deteriorated as the number of apertures was reduced from 64 to 9.