Method and device for determining an orientation of an object

Patent metadata

Field	Value
Publication number	US-9720087-B2
Application number	US-201314440063-A
Country	US
Kind code	B2
Filing date	Oct 29, 2013
Priority date	Oct 31, 2012
Publication date	Aug 1, 2017
Grant date	Aug 1, 2017

Abstract

The invention relates to a method for determining a spatial orientation of an auxiliary measurement object for a laser tracker, said measurement object having reference features which provide points of light. The tracker has a base, a support which can be pivoted in a motorized manner, a pivoting unit which can be rotated about a tilting axis in a motorized manner and which comprises an image capturing unit for capturing an image of the points of light, and a beam source for emitting a laser beam. According to the method, an image is captured in the direction of the auxiliary measurement object with respective capturable points of light, and the spatial orientation of the auxiliary measurement object is derived from image positions in the image for the points of light captured in the image using an image analysis.

First claim

What is claimed is:

1. A method for determining a spatial orientation of a measuring aid object, which has reference features, which are attached in a defined spatial relationship and provide light spots, for and using a laser tracker having:
a base, which defines a standing axis,
a support, which is pivotable by a motor about the standing axis in relation to the base,
a pivot unit, which is rotatable by a motor about a tilt axis in relation to the support, having an image capture unit for capturing an image of the light spots,
a radiation source for emitting a laser beam,
a distance measuring unit for measuring the distance to the measuring aid object by means of the laser beam, and
an angle measuring functionality for determining an emission direction of the laser beam in relation to the base;

the method comprising:
capturing an image in the direction of the measuring aid object having light spots, which can each be captured in dependence on at least one position and/or on an alignment of the measuring aid object;
deriving a spatial orientation of the measuring aid object by means of image analysis from image positions in the image for the light spots captured in the image;
defining a local consideration criterion with respect to an appearance of an individual light spot in the image for the image analysis or a global consideration criterion with respect to a position relationship between a number of light spots in the image is defined for the image analysis;
performing a check of a fulfillment of the local or global consideration criterion for at least one of the light spots captured in the image; and
if the consideration criterion is not fulfilled, weighting the at least one of the light spots captured in the image in reduced form for the derivation of the spatial orientation.

2. The method as claimed in claim 1 , wherein:
the local consideration criterion defines an image attribute for the appearance of at least the one of the light spots in the image.

3. The method as claimed in claim 1 , wherein:
the local consideration criterion defines at least one of a setpoint shape, a setpoint spatial extension, a setpoint brightness distribution, a setpoint total intensity, a setpoint contrast as the image reference.

4. The method as claimed in claim 1 , wherein:
the global consideration criterion defines a relative spatial setpoint positioning of the image positions in the image for the number of the light spots captured in the image in consideration of a respective orientation of the measuring aid object.

5. The method as claimed in claim 1 , wherein:
the global consideration criterion defines a relative spatial setpoint positioning of the image positions in the image for the number of the light spots captured in the image.

6. The method as claimed in claim 1 , wherein:
the local or global consideration criterion is derived from at least one of the captured image, a respective graphic depictions of the light spots in the image, and a comparison of the respective graphic depictions of the light spots.

7. The method as claimed in claim 1 , further comprising:
capturing offset in time at least one additional image having the light spots; and
performing a check of a fulfillment of the local or global consideration criterion for at least one of the light spots captured in the additional image; and
if the consideration criterion is not fulfilled, weighting the at least one of the light spots captured in the additional image by a comparison of the appearance of the individual light spot in the additional image or by a comparison of the respective image position for the individual light spot in the additional image.

8. The method as claimed in claim 1 , wherein:
performing a check of a fulfillment of the local or global consideration criterion for at least one of the light spots captured in the image includes deriving an item of graphic information from the image for the at least one of the light spots captured in the image, wherein the graphic information includes at least one of an actual shape, an actual spatial extension, an actual brightness distribution, an actual total intensity, and an actual contrast which is captured for the light spot in the image; or
for the check of the fulfillment of the global consideration criterion, an image position, which is determined by means of image processing, for the at least one of the light spots in the image, which are captured in the image, is used, in particular wherein the image position is determined by means of focus calculation in the image based on a brightness distribution.

9. The method as claimed in claim 1 , wherein:
the image position is determined by means of focus calculation in the image based on a brightness distribution.

10. The method as claimed in claim 1 , wherein:
performing a check of a fulfillment of the local or global consideration criterion for at least one of the light spots captured in the image is based on at least one of a spatial structure of the measuring aid object, a measurement space, a position of the measuring aid, and a position and dimensioning of a visual obstruction.

11. The method as claimed in claim 1 , further comprising:
determining at least partial concealment for at least the one of the light spots captured in the image, wherein if at least partial concealment of the light spot is present, this light spot is weighted in reduced form for the derivation of the spatial orientation.

12. The method as claimed in claim 1 , further comprising:
determining a comparison quality value, which specifies a degree of correspondence of consideration criterion, and an item of image information by comparing the consideration criterion and the item of image information; and
defining a confidence range for the comparison quality value, wherein the item of image information for at least the first light spot is derived from the captured image, wherein
if a presently determined comparison quality value in the scope of the check of the fulfillment of the local or global consideration criterion for the at least one of the captured light spots is provided within the confidence range, a consideration is performed, and if the determined comparison quality value is present outside the confidence range, a reduced weighting of the light spot is performed for the derivation of the spatial orientation.

13. The method as claimed in claim 1 , wherein:
in the scope of the check of the fulfillment of the local or global consideration criterion for each of the light spots captured in the image, an individual residual is determined and it is checked whether the respective residuals lie within a settable expectation range, wherein if one or more residuals are present outside the expectation range, the corresponding light spot or spots are weighted in reduced form for the ascertainment of the comparison quality value are excluded for the derivation of the spatial orientation.

14. A laser tracker for the position and/or alignment determination of a measuring aid object, which has reference features, which are attached in a defined spatial relationship and provide light spots, the laser tracker comprising:
a base defining a standing axis;
a support pivotable by a motor about the standing axis in relation to the base;
a pivot unit rotatable by a motor about a tilt axis in relation to the support, having an image capture unit for capturing an image of the light spots;
a radiation source for emitting a laser beam;
a distance measuring unit for measuring the distance to the measuring aid object by means of the laser beam;
an angle measuring func

Assignees

• Leica Geosystems Ag

Inventors

• Christen Andreas
• Wildi Konrad
• Markendorf Albert

Classifications

• G01S5/16

  using electromagnetic waves other than radio waves · CPC title

• G01S7/497 Primary

  Means for monitoring or calibrating · CPC title

• G01S17/42 Primary

  Simultaneous measurement of distance and other co-ordinates (indirect measurement G01S17/46) · CPC title

• G01S17/86 Primary

  Combinations of lidar systems with systems other than lidar, radar or sonar, e.g. with direction finders · CPC title

• G01S17/48

  Active triangulation systems, i.e. using the transmission and reflection of electromagnetic waves other than radio waves · CPC title