WO1992008105A1

WO1992008105A1 - Method and device for position measurement

Info

Publication number: WO1992008105A1
Application number: PCT/SE1991/000741
Authority: WO
Inventors: Rudolf Wiklund
Original assignee: Geotronics Ab
Priority date: 1990-11-02
Filing date: 1991-11-01
Publication date: 1992-05-14
Also published as: SE9003500D0

Abstract

The invention relates to a measuring instrument for determining the position of at least one measuring point (C) in the vicinity of the measuring instrument, and a method for determining the position of at least one measuring point. The measuring instrument includes receiver equipment having a receiver antenna (1, 2, 3) for indicating signal positions, e.g. in accordance with GPS, and a measuring-point sighting device (8; 16) which is connected to the receiver equipment and which can be brought into alignment with the measuring point. In addition to a standard position determining arrangement, the receiver equipment is also provided with a direction detecting device (5, 6; 15a, 15b, 15c), which functions to indicate the horizontal direction from the measuring instrument to at least one selected transmitter unit. The instrument also includes an arrangement (6, 11) which provides a reference direction for measuring horizontal angles of the measuring-point sightinig device on the basis of the indicated direction to the selected transmitter unit.

Description

METHOD AND DEVICE FOR POSITION MEASUREMENT.

The present invention relates to a method for establish¬ ing the position of one or more measuring points with the aid of signals received from a GPS-receiving system, and also to an instrument for carrying out the method.

Prior Art Techniques

When defining the positions of measuring points and/or when marking out an area with the intention of defining the boundaries of a plot of land, a road or highway, etc., it is normal practice to place a distance meter, or telemeter, in a central position. Subsequent to having adjusted the position of the instrument so that the symmetry line of the instrument stand extends exact¬ ly vertical, the instrument is used to make a reference measurement on at least one reference point in the terrain, for example a church steeple, a house, or like landmark, whose position is known beforehand. The instrument measures the distance from and the direction to each reference point and calculates its position with the aid of the reference measuring results. The instru¬ ment is then used to define the intended measuring points. One problem with this system is that it is often relatively difficult to find reference points whose positions are known.

In recent times, position establishment has been performed with the aid of special positioning satellites, such as the Navstar satellites projected into space by the U.S.A;, which produce very accurate results. The system is called the GPS-system (Global

Positioning System) and is based on time measurement and on the simultaneous use of signals received from at least four satellites. This system enables an area to be marked out by a single person carrying a GPS- antenna and receiver to the various marking-out points in the terrain. One problem with this type of system, however, is that it is necessary to chose measuring points where the satellite signals will not be obstructed. Thus, it is necessary to position the antenna of the GPS-system at a point where the system is free from shading or screening objects. It is necessary to measure or to define those measuring points which are located beneath outwardly jutting roofs or which are shaded by a tree, or are obstructed in some other way, with the aid of other methods.

The Objects of the Present Invention

The main object of the present invention is to provide measuring equipment with which the positions of measur- ing points are established or defined in accordance with the GPS-system, although with which the horizontal direction to a selected satellite can also be indicated.

Another object of the invention is to provide equipment which also will enable poisition establishment of measuring points which are hidden to the satellites of the GPS-system.

A further object of the invention is to provide measur- ing equipment establishing the position of the equipment as well as its alignment in a horizontal plane.

Still another object of the invention is to provide measuring equipment for establishing or defining the position of a measuring point and/or for marking out an area, which includes a measuring station having tele- meter equipment of the EDM-type and which is intended to be placed centrally and can be brought into alignment with a plurality of measuring points for marking-out points during a measuring sequence, and which will obviate the necessity of taking reference measurements on known points in the surrounding terrain.

Yet another object of the present invention is to pro¬ vide a method by means of which solely one measuring point having the possibility of signal reception is re¬ quired for the purpose of accurately determining the position of a target. This obviates the need for sever¬ al measuring points close to the target point.

The main object of the invention is achieved with a measuring instrument of the kind defined in the charac¬ terizing clause of the following Claim 1. Further features and further developments of the measuring instrument according to the invention and a method for defining the position of a measuring point are set forth in the remaining Claims.

Brief Description of the Drawings

So that the invention will be more readily understood and further features thereof made apparent, the inven¬ tion will now be described in more detail with reference to exemplifying embodiments thereof and with reference to the accompanying drawings, in which: Figure 1 is a schematic illustration of a first embodi¬ ment of a measuring instrument according to the invention; Figure 2 is a diagram relating to the received signal strength as a function of the angular rotation of the GPS-antenna in Figure 1; Figure 3 is a principle diagram illustrating angles measured with the aid of the measuring instrument illustrated in Figure 1;

Figure 4 is a diagram relating to the strength of sig¬ nals received from a variant of the embodiment illustrated in Figure 1;

Figure 5 illustrates schematically a second embodiment of a measuring instrument according to the invention;

Figure 6 illustrates in principle the processing of signals obtained from the GPS-antenna elements in the measuring instrument according to the Figure 5 embodiment; and

Figure 7 illustrates signals obtained from the GPS- antenna elements in the measuring instrument according to the Figure 5 embodiment.

The First Embodiment

A first embodiment of equipment constructed in accor¬ dance with the invention is shown in Figure 1. This equipment includes a GPS-antenna 1 with an earth plane 2, and a central antenna element 3 mounted on a rod 4. In accordance with the invention, the GPS-antenna is re- sponsive or sensitive to direction and in the case of this embodiment, the directional sensitivity of the antenna has been achieved by positioning close to the periphery of the antenna an upstanding wing 5 which is made of a material which dampens the carrier wave arriv- ing from the satellites. The wing 5, which is construc¬ ted as a signal dampening device, is rotated around the edge of the antenna, either by rotating the actual wing itself or by rotating the rod 4. The wing 5 has a vertical extension sufficient to dampen the carrier wave of a satellite which is located high in the sky. Al¬ though not shown, the wing may be mounted,so as to enable it to be raised and lowered. The Figure 1 embodiment also includes a unit 6 which includes a motor mounted on the rod 4. The unit 6 also includes a rota¬ tional angle sensor, e.g. a code-disc system or syngon element (not shown).

As beforementioned, as an alternative to rotating the rod 4, means may be provided for rotating the actual wing itself. No separate embodiment which includes this latter facility is illustrated here. The angle through which the antenna is rotated is also detected in this latter embodiment, of course.

A sighting device 8, such as a telescope, is pivotally mounted on a stand 7, by placing said unit in a housing 9 mounted on said stand. The sighting device can be rotated or pivoted both in a horizontal plane and in a vertical plane, in a known manner, so as to enable said unit to be brought into alignment with a target point C.

The rotary angle sensor in the unit 6 functions to measure the angle of rotation between the rotatable rod 4 and the sighting device 8. The equipment used to define a sighting angle between a satellite which trans- its a signal, or a reference direction according to the GPS-system, and the sighting device 8.

Rotation in the vertical plane is measured with the aid of a vertical angle indicator 12, which is illustrated purely schematically in the Figure and which is prefer¬ ably of the pendulum type. A suitable vertical angle indicator intended for this particular purpose is de¬ scribed in U.S.A. Patent Specification No. 4,277,895.

Mounted on the stand 7 is also a standard type of verti¬ cal position indicator 10 conventionally used with this type of instrument and having two mutually perpendicular level indicators of the spirit-level kind which enable the stand, and therewith also the rod 4, to be brought precisely to a vertical position. This will position the earth plane 2 of the GPS-antenna 1 horizontally.

The equipment also includes a calculating or computing unit 11 which comprises a receiver unit for receiving signals from the GPS-antenna 1. The computing unit also receives signals from the rotary angle indicator 6 and the vertical angle indicator 12 (not shown) .

Because the signal damping device 5 can be rotated around the central antenna element 3 of the antenna 1, the device is able to dampen the ability to receive signals within a defined and variable angular range.

When the signal dampening device 5 is rotated around the antenna centre, satellite signals which arrive from the direction which is obstructed by the signal damping device are either dampened or extinguished. There is therewith obtained in the receiver of the calculating unit 11 a variation in strength of the signal received, this strength variation being dependent on the direction in which the signal damping device faces.

Figure 2 is a curve which illustrates how the strength of the signal received varies in relation to a reference signal with the angle of rotation. This reference signal may be obtained, for instance, by measuring the strength of signals received from a selected satellite while rotating the wing 5 through one or more revolu¬ tions and recording the instantaneous variants in signal strength. It should be noted that further variations in signal strength may occur, due to signal reflection from objects in the surroundings. The satellite moves in a well known manner, which is programmed in the receiving unit 11, whereas the reflected signals move along other paths, particularly in another directions, since they are reflected and have a phase which is different to the phase of the direct signal. Consequently, those varia- tions in the received antenna signal which are due to such reflections can be eliminated by computer process¬ ing the signal, e.g. by autocorrelation.

A reduction in the strength of signals received between the rotary angle positions V and V are caused by s 6 passage of the signal damping device 5 through these angular positions between the antenna and the trans¬ mitter.

Figure 3 is a principle diagram which illustrates a measuring system according to one method according to the invention. In the case of this embodiment, the equipment includes only one telescope 8, as illustrated in Figure 1, such that only the direction to a measuring point is defined and not the distance from the equipment to said measuring point. Consequently, it is necessary to effect measurements on the measuring point C from two positions A and B, so as to enable the position of measuring point C to be determined by triangulation (the distance between the first mentioned two positions and the directions towards the point C become known) .

In order to obtain the reference direction prior to defining the direction towards the measuring point C, respective angles o and β are measured at the point of intersection of the normal of a signal-transmitting satellite in a horizontal plane through the measuring point and the direction towards the point C in the same horizontal plane, i.e. the horizontal sighting direction of the telescope 8, in the two positions A and B respec¬ tively. This is the direction which is indicated by the direction indicator 6 in the embodiment illustrated in Figure 1.

The positions of the satellites are well known at each moment in time, and data relating to these positions is stored in the receiver, in the computing unit 11.

The measurements made on the point C from the measuring points A and B make known the position of the measuring point A and the angle in the horizontal plane, A, S ,

-__.

C , and the angle γ in the vertical plane A, C, C , and

<__ A. also make known the position of the measuring point B and the angle β in the horizontal plane B, S , C , and

B B the angle η in the vertical plane B, C, C . It is also

B possible to calculate the positions of the points S and S at which the satellite normal intersects the two horizontal planes. The position of the measuring point C can be calculated from this data with the aid of geometrical methods well known to the person skilled in this art.

The method comprises the steps of:

SI: Placing the equipment in a measuring position A.

S2: Aligning the sighting device 8 with a point C.

Rotating the damping wing 5. Setting the reference level according to Figure 2. And measuring the vertical angle defined by the sighting device 8 with the unit 12.

S3: The following values are recorded:

1) The directional angle V of the signal damping s device in relation to the direction of the sighting device 8 in the horizontal plane of the equipment when the strength of the received signal from a selected satellite de¬ creases and passes through a reference signal level.

2) The time ts at which this occurs.

S4: The following values are recorded:

3) The directional angle V of the signal damping device in relation to the direction of the sighting device in the horizontal plane of the equipment when the strength of the signal received from the same selected satellite increases and passes through the reference signal level.

4) The time t at which this occurs. ' e

The aforesaid recorded values depend on the position of the selected satellite and also on signal strength and on the damping ability of the signal damping device.

S5: Calculating the angular position centrally between the recorded angular positions V S and V6, wherein information concerning the angle a in the hori¬ zontal plane of position A is obtained for the relevant position of the selected satellite.

S6: Repeating steps S2 to S4 a number of times and calculating the directional angle a of the selected satellite each time, and storing the value obtained.

S7: Repeating steps S2 to S6 for one or more of the remaining satellites. This step may optionally be omitted. Alternatively, the step may be coupled to a condition that it- need only be carried out when the spread between the angular positions calculated when measuring onto the first selected satellite is greater than a determined spread value. It will be understood that the repeated measurements are carried out uniformly and that the path travelled by the satellite between consecutive measurements can be determined.

S8: Defining the position (X , Y , Z ) of the point A via the GPS-system in a conventional manner.

S9: Moving the equipment to another geographical posi¬ tion, point B, and repeating the method steps S2 to S8.

S10: Calculating the position of the point C with the aid of geometrical formulae and with the aid of satellite data stored in the computing unit 11. The position of C is calculated a number of times with the aid of the data repeatedly determined and stored, and a mean value is formed from the calcu- lated positions.

When the satellite on which the angular positions V and V are measured moves only insignificantly between the times at which consecutive measurements are made, the angular position α or β between V and V can be

S 6 calculated by static calculation of a number of measure¬ ments already during the repeated recording of Vs and

Second Embodiment

In the case of this second embodiment, the unit 8 of the Figure 2 embodiment may have the form of a distance meter of the EDM-type (EDM = Electronic Distance Meter) , which can be directed onto the target point C. The distance meter may be provided conventionally with a simple sight or with a telescopic sight (not shown in the particular Figure since the difference from the Figure 1 embodiment is only marginal). In the case of this embodiment, the measurement effected on the point C can be carried out from solely one measuring point A. As is conventional when using an EDM-instrument, the measuring process can be carried out either on a prism, e.g. a cubic prism, placed at the target point C or may be carried out directly on the target point, by calcu- lating on the measuring beam effected directly by the target point (direct reflex). The latter alternative provides a slightly less accurate measuring result than the former process.

From a practical point of view, it may be beneficial to be able to also measure rotation of the housing 9 in relation to the stand. This can be effected with a rotary angle detector 9' . The use of a rotary angle detector 9' will facilitate the measuring procedure, since the detector 9' can be used, for instance, when defining a measuring point and/or when marking-out in a manner such that reference measuring to establish posi¬ tions and reference angle positions is carried out with the aid of GPS and the actual measuring sequence for the area concerned is then effected with the use of the rotary angle detector 9' to provide the horizontal angle in question. This enables an area to be surveyed much more quickly and with fewer calculations than when hori¬ zontal angles are defined against one or more satellites when measuring on each measuring point in the area.

Furthermore, surveying instruments provided with rotary angle detectors 9' are well known and, according to the invention, such a detector need only be complemented with a GPS-receiver with, a modified antenna in order to provide a reference, whereafter surveying of the area concerned is effected in a conventional manner without modifying calculations during a surveying sequence, as distinct from conventional procedures.

The computing unit 11 can then function in accordance with the following method steps of:

SI: Placing the equipment in a measuring position A. S2: Bringing the sighting device 8 into alignment with a point C.

Rotating the damping wing 5. Setting the reference level according to Figure 2. Measuring the vertical angle defined by the sighting device 8 with the unit 12. And measuring the distance from the measuring equipment to the measuring point C.

S3: The following values are recorded:

1) The directional angle V of the signal damping device in relation to the direction of the sighting device 8 in the horizontal plane of the equipment when the strength of the signal received from a selected satellite decreases and passes through a reference signal level.

2) The time ts at which this occurs.

S4: The following values are recorded:

3) The directional angle V of the signal damping device in relation to the direction of the sighting device 8 in the horizontal plane of the equipment when the strength of the signal received from the same selected satellite increases and passes through the reference signal level.

4) The time t at which this occurs.

' e The aforesaid recorded values are dependent on the position of the satellite and also on signal strength and on the damping ability of the signal damping device.

S5: Calculating an angular position centrally between the recorded angular values V and V , wherein s e information relating to the angle α in the horizontal plane of the position A is obtained for the prevailing position of the selected satellite.

S6: Repeating steps S2 to S4 a number of times. The directional angle of the selected satellite is calculated each time and the angular values are stored.

S7: Repeating steps S2 to S6 for one or more of the remaining satellites. This step may optionally be omitted. Alternatively, the step may be coupled to a condition that the step need only be carried out when the spread between the angular positions cal¬ culated when measuring against the first selected satellite are greater than a determined spread value. It will be realized that the repeated mea- surements are taken uniformly and that the distance moved by the satellite between consecutive measure¬ ments can be determined.

S8: Defining the position (X A_., Y__-_., Z -A) of the measuring point A conventionally via the GPS-system.

S10: Calculating the position of the measuring point C with the aid of geometrical formulae and satellite data which are stored in the calculating unit 11. The position of C is calculated repeatedly with the aid of the data repeatedly determined and stored, and a mean value of the calculated positions is formed from this data.

Sllr Optionally establishing a reference angular posi- tion in the horizontal plane and marking this posi¬ tion on the horizontal angle indicator 9', and carrying out a series of measurements against dif¬ ferent measuring points in the terrain with the aid of the angle measuring device 9'.

The Figure 1 embodiment has been described as having solely one single damping wing. In order to obtain a further indication of the satellite position, the wing 5 can be constructed so that the side of the wing which faces towards the antenna element 3 will reflect sig¬ nals. Figure 4 illustrates the signal received thereby from the antenna element 3 of the antenna 1. The angu¬ lar positions for passage through an upper reference level can therewith also be indicated and the angular position therebetween is calculated as a complement to the angular positions calculated for passage through a lower signal level.

The signals obtained from a wing that has been provided with a reflector (e.g. a mirror, which may also be curved), however, are dependent on the distance from the wing to the antenna element 3. This distance corres¬ ponds to the wavelength of the carrier wave of the satellite signal. Thus, when the distance between the wing and the antenna element 3 lies in the proximity of one or more full wavelengths, the full-line curve shown to the right in the Figure is obtained, with amplifica¬ tion of the received signal through the reflector. On the other hand, when said distance lies in the proximity of half a wavelength or some odd multiples of said wave¬ length, the signal is extinguished to some extent, as illustrated by the broken-line curve. An embodiment where the reflecting wing is positioned at approximately half the wavelength of the satellite carrier wave is to be preferred, since this arrangement will result in a small and compact GPS-antenna 1. It is not possible, however, to determine the distance from the reflector to the antenna element exactly so as to reflect an odd number of half wavelengths of the satellite signal, and the computing unit 11 is only able to calculate values that are applicable in each prevailing case, on the basis of the known distance between the reflector and the antenna element 3 and the instantaneous height of the satellite above the antenna. It is thus essential that this data is known.

Although not shown, two signal damping wings may be placed diametrically opposite one another, where one wing solely has a signal-damping function and the other wing has both a signal-reflecting and a signal-damping function. This arrangement will result in a more exten¬ sive decrease in signal level than that shown to the right in Figure 4 at the angular position of the wing arrangement at which reflection has effect, because the signal level is both dampened by the damping wing and reduced due to extinguishing of the signal by diffrac¬ tion of the reflecting wing.

It should be noted, however, that a certain positional error may be caused by double indication, partly because of the different positions of the wing in relation to the antenna element 3 and partly because of movement of the satellite with time, although this positional error can be compensated for when processing the signals received. However, there is obtained a variation in signal strength such as to indicate at least one of the level through-passes during one revolution. As will be understood, steps S3-S5 above will be slightly modified, because level through-pass is indicated twice with each revolution instead of only once.

Third Embodiment

According to a third embodiment of the invention illus¬ trated in Figure 5, the equipment includes an antenna 14, an earth plane 2 and three antenna elements 15a, 15b, 15c. The three antenna elements are arranged at a given distance from the centre of the antenna, for instance at an angular spacing of 120 degrees.

The equipment illustrated in Figure 5 also includes an EDM-instrument 13 which is mounted on a stand 16 and which can be rotated in a vertical direction by means of a knob or wheel 17, and further includes a sighting device 18 by means of which the instrument 13 is brought into alignment with the target point C. The EDM-instru- ment is provided, in a known manner, with an arrangement for fine adjustment of the alignment with the target point when said target point is provided with a prism and with a vertical angle indicator 10, for instance a pendulum-type indicator. The EDM-instrument can be rotated in a horizontal plane relative to the instrument stand, by means of a horizontal rotational device 19, which is provided with a horizontal angle indicator (not shown) .

The antenna 14 of the Figure 5 embodiment is not rotat- able relative to the unit 16 around a vertical shaft. With three or more receiving antennae or antenna ele¬ ments, the direction to the satellite whose signal shall be received is established by comparison between the mutual phase positions of the signals received. This can be achieved by processing the signals in seve¬ ral different ways. A principle for signal processing in three stages is illustrated in Figure 6. The antenna elements 15a, 15b, 15c may be placed so close together that the difference in the propagation path between the satellite signals which impinge on the elements lies well within 1/2 wavelength of the satellite carrier frequency. It is also conceivable, however, to place the antenna elements much further apart. In order to be able to establish the propagation path differences and the direction towards the selected satellite obtained from these differences on the basis of analyzing the phases of said signals, it is essential that the mutual positions of the antenna elements 15a, 15b, 15c are accurately determined.

The signals received from the three antenna elements 15a, 15b and 15c are shown in Figure 7 and the signals are phase-analyzed in a first stage SB1, such that the phase differences φ and φ (see Figure 7) in respect of the antenna.element which lies first in phase and which is thus the antenna element of said three antenna elements which lies nearest the satellite can be indicated. Phase analysis can be carried out in several different ways, all of which are well known to the skilled person and are therefore not described here.

The difference in the paths travelled by the three signals before being received by respective antenna elements is calculated in the second step SB2 of the signal processing stage.

In the third step SB3 of the signal processing stage, the horizontal direction of the antenna in relation to the satellite is calculated geometrically with the aid of information relating to the calculated propagation paths and the mutual positioning of the antenna elements 15a, 15b, 15c. This calculation is well known to one skilled in this art and will not therefore be described in detail. It can be mentioned, however, by way of example, that an extremely simple calculation can be made when two of the antenna elements 15a, 15b, 15c re¬ ceive signals which have mutually the same phase. The direction will then lie midway between these elements and through the centre and outwards, when the signal of the third antenna element lags in phase and in the other direction when said signal precedes in phase.

In this case, the antenna 14 is fixedly connected to the holder of the EDM-instrument 16 and the indicated direc- tion to the satellite is therefore placed in relation to the horizontal direction of the instrument 16, i.e. it is the horizontal angle between the instrument and the selected satellite that is measured.

The invention has been described in the aforegoing with reference to the use of the special position determining system GPS. It will be understood, however, that the invention can be equally as well applied with other position determining systems, for example systems which utilize ground-located transmitter units which are placed in known positions in the area to be surveyed.

Claims

1. A measuring instrument for obtaining measuring data relating to the position of a measuring point, compris¬ ing receiver equipment which includes a receiver antenna (1-3; 14) for indicating the position of signals gene¬ rated by position-determined transmitter units, such as satellites, for instance included in a GPS (Global Position System), c h a r a c t e r i z e d in that in addition to including a standard position determining arrangement, the receiver equipment also includes a direction detecting arrangement (5, 11; 15a, 15b, 15c, Figures 6 and 7) , by means of which the horizontal direction from the measuring instrument to at least one transmitter unit selected from said transmitter unit can be indicated.

2. An instrument according to Claim 1 for determining at least one measuring point (C) in the vicinity of said measuring instrument, comprising a measuring-point sighting device (8; 16) which is connected to the re¬ ceiver equipment and which can be brought into alignment with said measuring point, c h a r a c t e r i z e d by an arrangement (6, 11, Figures 6 and 7) which func¬ tions to provide a reference direction for measuring the horizontal angle of the measuring-point sighting device on the basis of the indicated direction towards the selected transmitter unit.

3. An instrument according to Claim 1 or 2, c h a r ¬ a c t e r i z e d in that the receiver antenna of said direction detecting equipment includes a damping device (5) which can be rotated around a central antenna unit (3) and which functions to dampen signals received by the antenna unit around the same frequency as the carrier wave of the transmitter unit and arriving from the direction in which the damping device is placed in relation to said antenna unit (3) .

4. An instrument according to Claim 1, 2 or 3, c h a r a c t e r i z e d in that the receiver antenna of the direction detecting equipment includes a reflec¬ tor (5) which can be rotated around a central antenna unit (3) and which functions to reflect signals received by the antenna unit whose frequency is generally equal to the frequency of the carrier wave of the transmitter unit and which arrive from a direction opposite to which the reflector is placed in relation to the antenna unit (3) .

5. An instrument according to Claims 3 and 4, c h a r a c t e r i z e d in that the damping device and the reflector are incorporated in one and the same device which has a damping function on the side thereof which faces away from the antenna unit (3) and a re¬ flecting function on the other side thereof.

6. An instrument according to Claims 3 and 4, c h a r a c t e r i z e d in that the receiver antenna of the direction detecting equipment includes two devic¬ es which are diametrically opposed to one another and of which one device is a damping device (5) which can be rotated around a central antenna unit (3) and which functions to dampen signals received by the antenna unit whose frequency is approximately equal to the carrier wave of the transmitter unit arriving from the direction in which the damping device is placed in relation to the antenna unit (3), and of -which devices the other device is a combined signal-damping and signal-reflecting device (5) which can be rotated around a central antenna unit (3) and the side of which remote from the antenna unit (3) has a signal damping function and the other side of which has a signal reflecting function.

7. An instrument according to any one of Claims 3-5, c h a r a c t e r i z e d in that a first angle- detecting device (6) functions to detect the angle be¬ tween the position of the damping and/or reflecting device in relation to the antenna unit (3) and the measuring-point direction device (8) in a plane parallel with the rotational plane of the signal damping and/or signal reflecting device; and in that the receiver equipment obtains data concerning an angle indicated by the direction indicating equipment and the received signal strength and is intended to indicate said angle position when the signal strength passes outside a normal signal level, with a given deviation, during one revolution of the signal damping and/or signal reflect¬ ing device, and to calculate the horizontal angle to the selected transmitter unit on the basis of the angular positions indicated during one revolution.

8. An instrument according to Claim 1 or 2, c h a r ¬ a c t e r i z e d in that the receiver antenna of the direction detecting equipment includes at least three antenna elements (15a, 15b, 15c) which are mutually spaced in the horizontal plane, wherein the receiver equipment is intended to calculate the direction angle to the selected transmitter unit with the aid of a phase comparison between the carrier wave signals received by the three antenna units from the selected transmitter unit.

9. An instrument according to any one of the preceding Claims, c h a r a c t e r i z e d in that the measur¬ ing-point direction device (8; 16) includes a distance measuring device by means of which the distance between the measuring instrument and the measuring point can be measured.

10. An instrument according to any one of the preceding Claims, c h a r a c t e r i z e d in that the measur¬ ing-point direction device (8; 16) includes a vertical angle meter which functions to measure the angular position of the direction from the measuring instrument to the measuring point in a vertical plane.

11. An instrument according to any one of the preceding Claims, c h a r a c t e r i z e d in that the measur¬ ing-point direction device (8; 16) is included in equip- ment intended for surveying and/or marking out an area; and in that coaction between the receiver equipment with the receiver antenna is arranged for use to determine the position of the measuring equipment in the terrain and to provide a reference direction for horizontal angle measuring of the surveying and/or marking-out instrument.

12. A method for determining the position of at least one measuring point (C) in the vicinity of a measuring instrument which includes receiver equipment including a receiver antenna for indicating the position of signals generated by transmitter units, for instance transmitter units included in GPS (Global Position System), and a measuring-point sighting unit which is connected thereto and which can be brought into alignment with the measur¬ ing point, c h a r a c t e r i z e d by in addition to determining said position conventionally also indicating the horizontal direction to at least one satellite selected from said plurality of satellites; aligning the measuring-point direction devices (8) with the measuring point (C) and measuring the angle between the direction to the selected satellite and the direction of the measuring-point sighting device (8) in a symmetry plane of the receiver antenna; measuring the distance of the equipment from the measur- ing point (C) ; and calculating the position of the measuring point (C) with the aid of geometrical formulae and on the basis of satellite data stored in the receiver equipment.

12. A method according to Claim 11, c h a r a c ¬ t e r i z e d by repeatedly calculating the position of the measuring point (C) on the basis of data which has repeatedly been determined and stored; and by forming a mean value of the calculated positions.

13. A method according to Claim 11 or 12, c h a r ¬ a c t e r i z e d by measuring the distance to the measuring point (C) by moving the measuring instrument to a new measurement determining point and again easur- ing said distance by again aligning the measuring-point sighting device (8) with the measuring point (C) and again measuring the angle between the direction line to the selected satellite and the sighting line of the measuring-point sighting device (8) in a symmetry plane of the receiver antenna.

14. A method according to Claim 11 or 12, c h a r ¬ a c t e r i z e d by measuring the distance to the measuring point (C) by measuring the distance to said measuring point directly.

15. A method according to Claim 14, c h a r a c ¬ t e r i z e d in that a reference angle position in the horizontal plane is determined through the measured angle between the direction towards the selected satel¬ lite and the direction of the measuring-point sighting device (8) in a symmetry plane of the receiver antenna and is marked for a separate horizontal angle meter (9') for the measuring-point sighting device (9) , said device being a distance meter having a conventional EDM- instrument; and in that a series of measurements to different measuring points in the terrain is then car¬ ried out with the aid of this angle meter 9' .