DD281245A5 - SUSPENSION OF A PHOTOGRAMMETRIC AIR IMAGING CHAMBER - Google Patents

Abstract

The invention relates to the suspension of a photogrammetric Luftbildmeszkammer. In order to reduce the image migration and increase the accuracy of aerial photography, a second control loop is provided in addition to a first control loop which compensates the determined by a control or Navigationsgeraet Abdriftwinkel on the Meszkammer, the Abdriftwinkelgeschwindigkeit the Luftbildmeszkammer to zero or on a Correction angle velocity derived from the control deviation of the first control loop. Applicable in photogrammetric recording systems. Fig. 2 {Luftbildmeszkammer; Suspension; Drift angle; Control loop; Drift angular velocity; Angle sensor}

Description

For this 1 page drawings

Field of application of the invention

The invention preferably finds application in photogrammetric Luftbildmeßkammern, which are suspended in horizontally stabilized platforms.

Characteristic of the known state of the art

Practical results of image flights under turbulent flight conditions show that despite image migration compensation and dynamically stabilized platforms, uncompensated image migration components are still present due to azimuthal rotational movements of the aircraft. Under moderate turbulent flight conditions, angular velocities up to 37s are measured at frequencies of 0.5 Hz. The resulting image migrations are Δβ'κ = r · sin (κ · t), where Δβ'κ: image migration amount

r: radius of the affected image detail from the center of the image

κ: azimuthal angular velocity

t: exposure time

For example, with an azimuthal angular velocity of 27 s and an exposure time of Vicds in the corners of a 23 × 23 cm ² measuring chamber, this indicates an image migration of 56 μm.

Known stabilized suspensions for Luftbildmeßkammern (SU 448442, US 3703999) stabilize only the two horizontal tilt axes, therefore can not compensate for this error.

Object of the invention

The aim of the invention is to reduce the image migration and the associated increase in accuracy of aerial photography.

Explanation of the essence of the invention

The object of the invention is to largely compensate for the disruption caused by azimuthal rotational movements of the aircraft in aerial photography.

The object is achieved with a suspension of a photogrammetric Luftbildmeßkammer containing a first control loop for correcting the Flugzeugabdriftwinkels, which compensates the determined by a control or navigation Abdriftwinkel on the measuring chamber, achieved in that a second control loop is provided, the Abdriftwinkelgeschwindigkeit the Luftbildmeßkammer controls to zero or to a correction angular velocity, which is derived from the control deviation of the first control loop. An advantageous embodiment of the invention is that over the first control loop, consisting of an angle sensor which measures the actual Abdriftwinkel between Luftbildmeßkammer and aircraft, and a first summer, which compares this actual value with the drift setpoint of the control unit, the resulting Control deviation via a limiter amplifier and a level controller is fed to a second summer of the second control loop as angular velocity setpoint, is compared by this with the angular velocity actual value of an associated with the Luftbildmeßkammer angular velocity sensor and the resulting difference as a manipulated variable via a controller and a drive on the Measuring chamber acts until the angular velocity is proportional to the output level of the level controller.

Furthermore, it is favorable that the output of the Begrenzerverstärkers leaves a low-pass large time constant with the input of a window area, the output level of the level controller switches to a larger value. This is the case if there is a one-sided control deviation of the first control loop over a longer period of time, ie that is, the absolute drift position has a larger difference between the setpoint and the actual value (for example, after a flown curve). The switching of the level control now causes a greater correction speed of the second control loop, whereby the new drift position is reached faster. The determined in any manner aircraft drift angle can also be compared in a computer with the actual drift angle of Luftbildmeßkammer, the calculator the Begrenzerverstärker the corresponding correction signal supplies and level switching of the level control can also be made by the computer according to any criteria. The angular rate sensor associated with the aerial image measuring chamber may be replaced by a sufficiently sensitive angular rate sensor with a downstream integrator.

embodiment

The invention is explained in more detail below with reference to schematic drawings. Show it:

Fig. 1: A schematic representation of the suspension of Luftbildmeßkammer

 2 shows a block diagram of the arrangement according to the invention.

The chamber 1 is mounted in a drift rotary bearing 14, which is arranged in the suspension upper part 15. The upper part 15 rests on a lower part 16 above a leveling direction. The drift angle between the chamber and the aircraft is measured by an angle sensor 7, which is firmly connected to the upper part 15.

The angle between pivot bearing 14 and Obeiteil 15 is set by a drive 5, which is also firmly connected to the upper part 15. At the pivot bearing 14, an angular velocity sensor 2 is provided. As shown in FIG. 2, the angular velocity sensor 2, together with the summer 3, the controller 4 and the drive 5, form a control circuit which sets the azimuthal angular velocity of the measuring chamber 1 at an angular velocity which is proportional to the output signal of the level controller 12 (FIG. normally zero). If the measuring chamber 1 at the beginning of the flight path is aligned with it, the measuring chamber always remains constantly aligned with the route during the recording of the aerial images over the route, independently of dynamic azimuthal rotations of the aircraft, e.g. caused by turbulence or correction maneuvers of the pilot.

Since this fast loop fixes the measuring chamber in any azimuthal position, it is superimposed on him another slow control loop, the alignment of the measuring chamber to the flight path we allows the conventional drift control. For this purpose, another measuring transducer 7 (angle measurement eg with potentiometer) is provided, which measures the angle between measuring chamber suspension 15/16 (identical to aircraft drift) and measuring chamber 1. This measured value (actual value) is compared in summer 8 with the desired value. The result is a control deviation which, via the limiter amplifier 11 and the level controller 12, is fed to the adder 3 of the fast control loop as command variable for the desired angular velocity for drift correction.

In the normal case (during aerial photography), the correction angular velocity is set so small (eg 0.2 ° / s) that the resulting image migration in the aerial images remains negligibly small. The dynamic azimuthal aircraft oscillation superimposed on the angle value of the transducer 7 (control of the fast control loop) is thereby integrated as far as possible by the much slower tracking of the slow control loop. By changing the Ad, iftwinkelsollgröße results in a one-sided correction signal at the output of the limiter amplifier 11, which is applied until the measuring chamber 1 is tracked and the signal of the angular difference after the summer 8 again oscillates zero point symmetry.

For the correction 'big', ier angle amounts, such as the z. For example, after a turnaround is required, the new positioning of the slow correction angular velocity M-chamber would take too much time, for which purpose the correction signal to the limiter amplifier 11 will pass through a low pass (with relatively large time constant) window discriminator 10 If, after a defined time (eg, 0 s), the low-pass output leaves the window discriminator window, the latter switches the level adjuster 12. The totalizer 3 is now subjected to a much larger reference variable, so that the correction of the If the intended drift position is reached, the signal at the low-pass output becomes smaller again and the window discriminator switches the level control back to normal (slow) correction angle speed.

The drift setpoint is manudl measured by a controller 6 as in classical unstabilized systems and electrically transmitted to the measuring chamber drift control by a transducer (potentiometer), or a micro-processor 13 accepts the drift setpoint from any system (e.g. a control unit 6 or a navigation system), the drift-actual value of the transmitter 7 and supplies a corresponding Korrekiursignal (according to target-actual-value comparison) to the Begrenzerverstärker 11. A microprocessor 13 can also intervene in the level control 12 and other criteria turn the quick-drift positioning on and off.

Claims (5)

1. Suspension of a photogrammetric Luftbildmeßkammer containing a first control loop for correcting the Flugzougabdriftwinkeis that compensating the determined by a control or navigation Abdriftwinkel transmits to the measuring chamber, characterized in that a second control loop is provided, the Abdriftwinkelgeschwindigkeit the Luftbiidmeßkammer to zero or to a correction angular velocity that is derived from the control deviation of the first control loop. 2. Suspension according to claim 1, characterized in that over the first control loop, consisting of an angle sensor which measures the actual Abdriftwinkel between Luftbildmeßkammer and aircraft, and a first summer, which compares this actual value with the drift setpoint of the control unit, the resulting control deviation is supplied via a limiting amplifier and a level adjuster, a second summer of the second control loop as angular velocity setpoint, is compared by this with the angular velocity actual value of an associated with the Luftbildmeßkammer angular velocity sensor and the resulting difference as a manipulated variable via a controller and a Drive acts on the measuring chamber until the angular velocity is proportional to the output level of the level controller. 3. Suspension according to claim 1 and 2, characterized in that the output of the Begrenzerverstärkers is further connected via a low-pass large time constant with the input of a window comparator, which, if the input signal leaves the window area, the output level of the level controller switches to a larger value. 4. Suspension according to claim 1 to 3, characterized in that the determined in any manner aircraft drift angle is compared in a computer with the actual Abdriftwinkel the Luftbildmeßkammer wherein the computer the limiting amplifier sin correction signal supplies and makes the level switching of the level adjuster. 5. Suspension according to claim 1-4, characterized in that the angular velocity sensor connected to the Luftbildmeßkammer is replaced by an angular acceleration sensor with downstream integrator.