The invention refers to the field of surveying technology, in particular to a process and arrangement for determining the position of a measuring point in geometrical space. The process and arrangement according to the invention can be used with currently available hard and software preferably at short ranges of 100 m with a measuring accuracy of (for example) 1 cm and an angular accuracy of 0.005 degrees. To carry out the process according to the invention two points of reference PI and PII are necessary whose space coordinates are known. PII should be at a distance from PI, the setup position for the digital video camera of the surveying instrument. The measuring point M in geometrical space to be located from point PI should be within 100 metres of PI. Greater distances (over 100 m) are conceivable at the price of lower accuracy (>1 cm). The process according to the invention is distinguished by the fact
a) that only one position of the surveying instrument is necessary (in position PI). From this point, the position of an imaginary beam is determined in geometrical space which joins the point M being surveyed with point PI. In this case, the position of the measuring point M in geometrical space is only known to be situated at some point on the beam, whose position in geometrical space is calculated,
b) and that the exact position of the measuring point in geometrical space can be determined when the surveying instrument is extended by a distance meter. By means of the distance meter, it is possible to determine the distance PI-M between the point PI and the measuring point M. Using the position of the “measuring-point beam” calculated in geometrical space, and the distance PI-M, it is possible to locate the exact position of the measuring point M in geometrical space.
With the process according to the invention, any point captured can be recorded automatically by computer control. The process is both flexible and economical.
Further advantages, features and potential applications of the present invention may be gathered from the description which follows, in conjunction with the embodiments illustrated in the drawings.
An example of the sequence of the process according to the invention for determining the position of a measuring point and of the arrangement required for determining the position of a measuring point is shown in the drawings and is described in more detail below.
The example of the invention refers to a geometrical space defined by cartesian x-y-z coordinates. Theoretically, however, the invention may also refer to geometrical spaces structured in different ways than in cartesian coordinates.
It should be noted that the conversion of coordinate systems is known.
In addition, to simplify the description, it should also be noted that the following mathematical processes are also known:
a) the calculation of the position of an imaginary beam in three-dimensional space using the x-y-z coordinates of two points located on the beam, and
b) the calculation on a screen plane of the position of a beam in three-dimensional space passing through points G and H by means of the known position of a beam in three-dimensional space on which a first point G (not shown) with known space coordinates is located, and by means of the known x-y screen coordinates of the optically created depiction of a second point in space H (not shown) with unknown space coordinates.
The screen image BO according to
For the alignment of the camera to a certain alignment position (here PI*) the camera is virtually rotated around point Z at the centre of its lens.
Depending on the circumstances, a very large number (one hundred or more) of such image marking points are normally are normally shown in a screen image. For reasons of simplicity, only five such marking points (P1′, P2′, P3′, P4′, P5′) are depicted in the image shown in
These marking points P1′, P2′, P3′, P4′, P5′ can be interpreted as the depictions of imaginary points in space P1, P2, P3, P4, P5 at the image-capturing level or in the corresponding computer image B1, although the space coordinates of these imaginary points in space P1, P2, P3, P4, P5 are unknown.
The computer first calculates the position of the optical axis A for the following camera position PI/PI*, where PI represents the setup location i.e. the reference point PI whose x-y-z coordinates are known coincides with the centre Z of the lens O of the camera K. For this setup position PI the camera adopts the alignment position PI*.
The direction of the optical axis A in three-dimensional space is calculated by the computer for this position PI/PI* of the camera K. This calculation is based on the specified x-y-z coordinates of the reference points PII and PI and the known distance components dx and dy between PZ and PII′ from
Depictions of the imaginary marking points P4 and P5 (still shown as P4′ and P5′ in image B1 in
By “angular deviation” the following is meant:
The triangles marked by the angle points P1′, P2′, P3′ and P1″, P2″, P3″ which are schematically indicated in B1 (according to
The depiction P′ in image B1 and the depiction P1″ in image B2 are assigned to the imaginary FIXED marking point P1 and the depictions P2′ and P2″ are assigned in the same way to the FIXED marking point P2 etc.
The depictions P1′, P2′ P3′ (of the imaginary FIXED marking points P1, P2, P3) in image B1 and the depictions P1″, P2″ P3″ (of the imaginary FIXED marking points P1, P2, P3) in image B2 are assigned to one another by computer to prevent confusion from occurring.
For such assignment, known computer programs are available (e.g. programs which function according to the Lucas-Kanada method which is based on the fundamental equation of optical flow; see “Lucas-Kanada method” in “Wikipedia” the free encyclopaedia).
In accordance with
In an angular calibration of the image-capturing level BE the position of this point is given with reference to the angle which is formed between the optical axis (passing through Z and PZ) and a beam passing through Z and that point. For this angle, two angular component values are formed which correspond to the cartesian coordinates x and y.
In other words, the distance between two points situated at a distance from one another on the image-capturing level BE or the screen level, can be defined by their differential angular values (angular deviations).
This means, for example, that for two imaginary FIXED marking points P1 and P2, the angular deviation between their depictions and P2′ (in image B1 in
For each of these imaginary FIXED marking points P1, P2 and P3 the direction of an imaginary beam passing through three-dimensional space is calculated (as a so-called initial direction value) from their depictions P1′, P2′, P3′ in image B1 (in
In addition, the computerised calculation of the direction of the optical axis in three-dimensional space for the digital video camera K in the alignment position PI** is based on the angular offset value between the depictions P1′ and P1″ of the FIXED marking point P1 and the initial direction value of that marking point P1.
Greater accuracy can be achieved where the computer calculates a mean value from the angular offset values of several FIXED marking points, where of each FIXED marking point (P1, P2, P3) of the offset value is defined as a shift in its depiction point P1′, P2′, P3′ in the screen image B1 in the screen image B1 in relation to its depiction point P1″, P2″, P3″ in its screen image B2, and where this mean value is used as the basis for calculating the direction of the optical axis in three-dimensional space for the digital video camera K in the alignment position PI**.
By taking a mean value, any disrupting effects (e.g. caused by noise) can be cut down to a minimum.
In addition, a measuring point M located in space is shown as M′ in the screen image B2. Its position is calculated as follows:
Computerised calculation of the horizontal mh and vertical my coordinate deviation from the depiction M′ with reference to PZ, and of the position of an imaginary beam in three-dimensional space, on which the measuring point M and the reference point PI lie, from the previously calculated position of the optical axis of the digital video camera K in the alignment position PI** and from the coordinate deviations mh and mv.
Using the process in accordance with the invention it is possible to determine not only the position of an imaginary beam in three-dimensional space on which a measuring point M and the centre Z of the lens of the digital video camera K lie. It is also possible to determine the absolute space coordinates of this measuring point by computer. To do this, the position of the imaginary beam and the distance from the centre Z of the lens (or of the setup position PI of the digital video camera K) to the reference point PII must also be known. This distance can easily be measured using a distance meter, e.g. a laser distance meter. When the distance is known, the computer can calculate the space coordinates of the measuring point from the known position of the imaginary beam and the distance value.
The distance meter is preferably arranged to rotate along with the camera. Its axis then correlates with the direction of the optical axis of the camera K. The computer carries out parallax compensation for deviations in the direction of both axes.
Any deviations in the reference point PI from the centre Z of the lens O which occur when positioning the digital video camera K are identified as deviation values by known processes of measurement. Using these deviation values, the computer then calculates an adjustment in such a way as if the digital video camera K were correctly positioned with the reference point PI coinciding with the centre Z of the lens O.
Similar adjustment calculations are known under the name of “parallax compensation”.
The digital video camera K has a digital zoom function. During the computer-controlled capture of image points on the screen B, certain selected areas of the image are zoomed and enlarged in the display.
According to the invention, a target point may also be selected and marked within the enlarged image of a space point using the screen grid. This permits much more precise marking of the target.
The setting of the digital video camera K to an alignment position (PI*, PII**) takes place by a screen control system. The current alignment of the digital video camera K is displayed on a screen and then adjusted by means of known control data in order to achieve the target alignment position (PI*, PI**).
It has already been noted that the x-y-z coordinates of the reference point PI can be specified. This can be done in a number of ways:
For example, the x-y-z coordinates of a previously known reference point may already be known. They can be determined using “traditional” surveying technology. According to the invention it is preferable to make use of the receiver of a satellite-navigation system to specify the x-y-z coordinates of the reference point PI. In the case of deviations in a receiver which is not aligned to the rotation point PI of the camera, a computer-calculated adjustment takes place as if the receiver were aligned to the rotation point PI of the camera.
According to the invention, an image camera with a three-dimensional image-capturing sensor can be coupled to the arrangement comprising the camera K, the computer C and the screen B. The purpose of this coupling is that the computer a) refers the image taken by the 3D camera for an “inaccurately” measured distance (measured by the “inaccurate” distance meter of the 3D camera) to an “accurately” measured distance (measured by the “accurate” distance meter of the arrangement according to the invention) and/or b) relates the relative image data for the image captured by the three-dimensional image-capturing sensor to the absolute space coordinates determined for a measuring point M of the object.
The screen level (
In an angular calibration (in degrees) the position of this point F′ is given with reference to the angle which is formed between the optical axis (which passes through Z and PZ in
For example, for two points situated at a distance from one another at the screen level, the distance between them can be defined by their differential angular values (angular deviations).
The arrangement for carrying out the process according to the invention for determining the position of a measuring point M in geometrical space comprises a digital video camera K a computer C with screen B, to which a digital video camera K is connected, for displaying the image captured by the camera K and for marking image points.
The digital video camera K is characterised by an imaginary optical axis A, a lens O, and an image-capturing plane BE. The optical axis A passes through the centre Z of the lens O and meets the image-capturing plane BE perpendicularly at point PZ. The digital video camera K can be rotated around the imaginary centre point Z of the lens O to different selected alignment positions PI*, PI**. The digital video camera K can be set up at an imaginary reference point PI with known space coordinates in such a way that this reference point PI coincides with the centre Z of the lens O (or in case of deviations, can be adjusted to it).
In a first alignment position PI* of the digital video camera K, the image BO (
The number of marking points (or their depictions) is unlimited. Depending on circumstances, this may be (e.g.) 100 or 1000. The marking points are generated automatically by computer. Their number depends on the characteristics of the captured image.
In the alignment position P** of the digital video camera K, the image B2 (
In addition, in the alignment position PI** according to image B2 (
A rotating arrangement is provided for the adjustment of the digital video camera K to one of its alignment positions (PI*, PI**). The adjustment of the digital video camera K to an alignment position (PI*, PI**) can be controlled by a screen image.
The surveying arrangement according to the invention can be extended by a receiver for a satellite-navigation system such as the Global Positioning System (GPS) for the accurate determination of position, which can be connected to the computer C. This receiver can be adjusted to the rotation point PI of the camera.
The surveying arrangement according to the invention can also be extended by a distance meter connected to the computer C. Preferably this can be mounted in such a way that it rotates with the digital video camera.
Deviations by the centre Z of the lens from the reference point PI when positioning the camera, deviations in the course direction of the optical axis A from the direction of aim of the distance meter, and deviations of the receiver axis from the rotation point Z of the camera can all be compensated by known methods such as parallax compensation.
The surveying arrangement can be coupled to a digital video camera comprising a three-dimensional image-capturing sensor. The digital video camera with the three-dimensional image-capturing sensor can be aligned with an object to be measured. The arrangement for determining the position of a measuring point M in geometrical space can be aligned with a point on this object. Through this coupling, the relative coordinates of an image captured by the three-dimensional image-capturing sensor can be related to the position of the measuring point determined according to the invention.
Digital video cameras of this type with a three-dimensional image-capturing sensor are commercially available, e.g. the “Swiss Ranger SR 4000” manufactured by MESA Imaging AG, Zürich, Switzerland.
Number | Date | Country | Kind |
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102011114115.8 | Sep 2011 | DE | national |