Pointing Errors Research Articles

Large Manual Pointing Errors, but Accurate Verbal Reports, for Indications of Target Azimuth

Many tasks have been used to probe human directional knowledge, but relatively little is known about the comparative merits of different means of indicating target azimuth. Few studies have compared action-based versus non-action-based judgments for targets encircling the observer. This comparison promises to illuminate not only the perception of azimuths in the front and rear hemispaces, but also the frames of reference underlying various azimuth judgments, and ultimately their neural underpinnings. We compared a response in which participants aimed a pointer at a nearby target, with verbal azimuth estimates. Target locations were distributed between 20 degrees and 340 degrees. Non-visual pointing responses exhibited large constant errors (up to -32 degrees) that tended to increase with target eccentricity. Pointing with eyes open also showed large errors (up to -21 degrees). In striking contrast, verbal reports were highly accurate, with constant errors rarely exceeding +/-5 degrees. Under our testing conditions, these results are not likely to stem from differences in perception-based versus action-based responses, but instead reflect the frames of reference underlying the pointing and verbal responses. When participants used the pointer to match the egocentric target azimuth rather than the exocentric target azimuth relative to the pointer, errors were reduced.

Localization of a remembered target under the influence of different head and body positions

Previous investigations analyzed the effect of semicircular canal stimulation on the localization of a remembered target and found additional indications that different head positions affect the test results. Therefore, the aim of the present study was to analyze the influence of different head and body positions on the localization performance towards a remembered target. The pointing error (PE) towards a remembered target was investigated in 24 right-handed volunteers (12 females, 12 males; mean age 23 years) under six different head and body positions (sitting upright with the head tilted forward/backward by 45 degrees ; sitting upright with a head displacement of 90 degrees to the right/left relative to the body; lying on the right/left side of the body). Evaluation parameters were the horizontal and vertical PE (in degrees). Head displacement to the left relative to the body led to a PE to the right side and head displacement to the right led to a PE to the left (ANOVA P<0.001; df=5; F=16.92). An upward PE occurred when the head was tilted forward by 45 degrees and a downward PE could be proved when the head was tilted backward by 45 degrees (ANOVA P<0.001; df=5; F=35.78). In summary, any change in the relation between head and body position led to a systematic PE towards the frontal plane of the body (i.e. the plane located in the axis between both shoulders). Taken together, the systematic PE in direction to the frontal body plane suggests that the location of the remembered target is coded and remembered in a frame linked to the body and not transformed into a head-centered frame of reference.

Effect of angular acceleration on the localization performance of a remembered target

Both the influence of a remembered "earth-fixed" target (RT) on the vestibulo-ocular reflex and the effect of "unilateral cold caloric vestibular stimulation" on the localization of a RT have previously been proved. As "unilateral caloric stimulation" is not a physiological stimulus, the aim of the present study was to analyze whether even physiological "bilateral vestibular stimulation" (rotation) is able to affect the RT position. The pointing error (PE) towards an RT both without and following angular acceleration was investigated in 24 healthy volunteers. Postrotatory nystagmus response was recorded by electronystagmography. Evaluation parameters were "nystagmus frequency", "total amplitude" and "velocity of the slow phase"; the horizontal and vertical PE. The fixation of an RT led to a significant reduction of about 28% in nystagmus amplitude compared to the test condition in darkness. "After rotatory stimulation" a systematic horizontal PE in the direction of the fast phase of the postrotatory nystagmus (direction of "illusory self-rotation") occurred and the magnitude of this PE increased significantly compared to the test situation "without vestibular stimulation", but showed only a non-uniform negative correlation with two of the nystagmus parameters. It has to be concluded that "after rotatory stimulation", in contrast to "unilateral cold caloric vestibular stimulation", the subjective sense of "illusory self-motion" leads to a horizontal PE in the direction of the nystagmus fast phases.

Measurements of Gun Tube Motion and Muzzle Pointing Error of Main Battle Tanks

Beginning in 1990, the US Army Aberdeen Test Center (ATC) began testing a prototype cannon mounted in a non-armored turret fitted to an M1A1 Abrams tank chassis. The cannon design incorporated a longer gun tube as a means to increase projectile velocity. A significant increase in projectile impact dispersion was measured early in the test program. Through investigative efforts, the cause of the error was linked to the increased dynamic bending or flexure of the longer tube observed while the vehicle was moving. Research and investigative work was conducted through a collaborative effort with the US Army Research Laboratory, Benet Laboratory, Project Manager – Tank Main Armament Systems, US Army Research and Engineering Center, and Cadillac Gage Textron Inc. New test methods, instrumentation, data analysis procedures, and stabilization control design resulted through this series of investigations into the dynamic tube flexure error source. Through this joint research, improvements in tank fire control design have been developed to improve delivery accuracy. This paper discusses the instrumentation implemented, methods applied, and analysis procedures used to characterize the tube flexure during dynamic tests of a main battle tank and the relationship between gun pointing error and muzzle pointing error.

Derivation of alignment tolerances for military laser systems

Pointing errors can compromise the performance of laser systems and cause numerous operational problems. Alignment tolerances for a generic electro-optical system comprising a laser are derived from first principles. The method applies to a sizeable class of problems but is particularly relevant to military applications such as laser target designation and rangefinding. It yields exact or conservative estimates in most cases of practical interest. Various results are explored from the point of view of employment methods and military deployment.

Frequency-Agility Processing to Reduce Radar Glint Pointing Error

A technique to reduce radar pointing errors due to glint using frequency agility and amplitude weighting is presented. The reduction in rms tracking error is developed into an equation dependent upon the original glint tracking error, σg, and the number of returns weighted, N. The rms tracking error is thereby reduced approximately by a factor of N. Finally, the equation formulated allows one to evaluate the reduction in glint error versus the number of frequencies chosen for frequency agility.

Third Order Aberrations in Cassegrain-Type Telescopes and Coma Correction in Servo-Stabilized Images

Pointing errors in telescopes carried by space vehicles can be compensated by servo-control of the secondary mirror. This introduces some aberrations in the stabilized image, the magnitude of which depends on the asphericity of the telescope mirrors. A configuration is presented in which the centered image of an off-axis object point is free from coma. The required aspheric corrections and the residual aberrations are calculated. Also included is a summary of the third order aberration constants for some well-known centered cassegrain-type telescopes.