WO1992019935A1

WO1992019935A1 - Compensation device for a height levelling instrument

Info

Publication number: WO1992019935A1
Application number: PCT/SE1992/000296
Authority: WO
Inventors: Rudolf Wiklund
Original assignee: Geotronics Ab
Priority date: 1991-05-08
Filing date: 1992-05-07
Publication date: 1992-11-12
Also published as: SE9101398D0

Abstract

The invention relates to an arrangement for compensating errors in measurement due to curved beam paths when determining heights with the aid of light emitted from a stationary height-determining instrument (H) onto a height-detecting arrangement (ST). The light transmitter unit of the height-determining instrument (H) emits at least two light beams, each having a different, narrow wavelength region. The height-detecting arrangement (ST) includes a light receiver unit which indicates vertical hits of light emitted from the height-determining instrument (1) in said wavelength regions. A calculating unit calculates a correction factor on the basis of the difference between the indicated hit-points and also calculates the height that the emitted light would have had without being bent, on the basis of the height of the indicated hit and on the basis of the correction factor and presents the calculated height on an indicating unit (IND).

Description

Compensation device for a height levelling instrument

The present invention relates to an arrangement of the kind defined in the preamble of Claim 1.

Leveling of ground preparation sites or building sites is often carried out with the aid of a height-determin¬ ing instrument which emits a light beam or laser beam that is caused to rotate at a given height in a hori¬ zontal plane which represents a reference plane or a plane located at a specific height in relation to a given "O"-plane. Another type of height-determining instrument, or leveling instrument, spreads a beam from a laser or a light-emitting diode (LED) in a horizontal plane. This beam can be pulsated so as to form a ^■■flash¬ ing" plane. A fully continuous beam which is intended for a laser plane, however, can also be spread out. Height is indicated with the aid of a readily-carried receiver unit which is placed in the measuring area in which it is suitable to make height determinations at that particular time. Naturally, several receiver units can be used simultaneously at different locations. The distance of the receiver unit from the height-determin- ing instrument may reach from 300 to 500 m. Equipment of this kind is used in many instances, for instance in excavation work, ground preparation and when laying asphalt.

In the case of optical instruments of this kind, the sighting line from the instrument to the target point is affected, among other things, by the influence of tem¬ perature on the density of the ambient air. The density of the air will vary as a result of heating or cooling of the ground in the region between the instrument and the target point, this variation resulting in a varying refraction coefficient in the abient air, i.e. a varying light refraction index, particularly in a vertical direction.

Those variations in the refraction coefficient that can occur, for instance on a sunny day over an asphalt surface, cause the transmitted light signal to be blurred when it meets the receiver unit. More important¬ ly, the refraction of light in the ambient air due to temperature gradients result in an incorrect indication of direction. When high degrees of accuracy are re¬ quired, it has been standard practice to carry out height-determining operations at times at which the temperature gradients in the ambient air are small, or to move the height-determining instrument and measure from different parts of the area to be levelled.

Variations in the refraction coefficient also create problems for optical distance measuring instruments of the EDM-type (EDM = Electronic Distance Measurement) . One solution to this problem with regard to such dis¬ tance measuring instruments is described in the Swiss Patent Specification No. 674 080. According to this patent specification, the target point is provided with an arrangement which emits two beams of light onto a receiver carried by the distance measuring instrument. The receiver functions to indicate the difference be¬ tween the directions of the two beams incident on the receiver and calculates a correction factor on the basis thereof. This calculated correction factor is sent to the calculating circuits of the instrument which adjust the height of the target point calculated thereby.

The object of the present invention is to solve the particular problems of compensating for differences in the refraction index in ambient air in association with height-determining instruments. This solution is based on the principle of refraction compensation described in the aforesaid Swiss Patent Specification No. 67480. The fact that the refraction index in air is different for different light wavelengths is utilized in this respect.

The object of the invention is realized with a height- determining arrangement of the kind defined in the characterizing clause of Claim 1. Other features and further developments of the invention are set forth in the remaining Claims.

According to the invention, the actual height-determin¬ ing instrument, itself transmits light within at least two, mutually different narrow wavelength regions, and the height-determining arrangement includes a light receiving unit having a hit-point indicator which indicates a hit on a level with the light emitted by the height-determining instrument within the aforesaid two wavelength regions or bands. The receiving arrangement is coupled to an arithmetical unit which calculates a correction factor on the basis of the difference between the hit-points on the hit-point indicator and also calculates the height which the emitted light would have had on the basis of the indicated hit on the level of emitted light within one of said wavelength bands and the calculated correction factor, and presents this calculated height on an indicating unit fitted to the height-indicating arrangement. The height-detecting device may be mounted on a staff which is placed by an operator at a location which shall have a given height, although it may also have the form of an arrangement which can be mounted on a wall or like structure.

The invention will now be described in more detail with reference to the accompanying drawings, in which

Figure 1 illustrates measuring equipment with a slightly exaggerated beam path between a height-determining instrument and a re¬ ceiver, in order to illustrate position¬ ing of different units forming part of the inventive arrangement;

Figure 2A illustrates schematically a first embodi¬ ment of a transmitted beam path and a receiver unit in accordance with the in¬ vention;

Figure 2B is an embodiment of a flow diagram illustrating the working method of a calculating unit included in the first inventive embodiment;

Figure 2C is a block diagram illustrating one em¬ bodiment of a circuit for calculating height deviations for a height-determin¬ ing instrument with which the light beams are rotated, and indicating the height;

Figure 3 illustrates schematically a second em¬ bodiment of emitted beam paths and a re¬ ceiver unit in accordance with the inven¬ tion, this embodiment being intended par¬ ticularly for generating a stationary light-plane from a height-determining instrument; and

Figures 4A are schematic, diagrammatic illustrations and 4B which explain the principles on which height compensation is calculated. Mutually similar parts in the different embodiments have been identified by similar reference signs.

Shown in Figure 1 is a height-determining instrument H which emits a rotating light beam S, or a stationary, optionally flashing laser plane. An operator P holds a height-detecting device, in the form of a staff ST, on which a receiver unit M is mounted and functions to receive and detect the height of the beam S from the instrument H. Height-determination is seldomly done at great distances between the height-determining instru¬ ment and the height-detecting device. Consequently, the beam may be narrow in a vertical direction when imping¬ ing on the receiver unit M of the height-detecting device, so as to have the form of a horizontal dash line, irrespective of whether height is determined with the aid of a rotating light beam, preferably with a laser beam, or a laser plane. In the case of the illus¬ trated embodiment, the receiver unit M is movable up and "down the staff, so as to enable the unit to be moved by the operator _'-to the position in which an incoming beam will strike the receiver unit.

When the height-determining process is carried out over a section of ground from which heat is emitted, for instance a sunlit asphalt surface, the refraction index will vary and the beam S will be deflected upwards.

In accordance with the invention, the height-determining instrument M emits beams' Lfl and Lf2 of two completely different wavelengths, of which, for instance, one light beam has twice the wavelength of the other. One light wavelength may lie within the visible wavelength range while the other may lie outside this range. It is easier for the operator to observe the height of solely one dash line on the receiver unit, the visible light. Accordingly, although not shown, the height-determining instrument may include a separate light emitting diode (laser) for each of the wavelength ranges concerned. The beams emitted by these diodes are reflected into the rotating arrangement of the light-determining instru¬ ment, or the light-plane propagating arrangement of said instrument, so that the beams will be emitted from the instrument at mutually the same height.

The receiver unit M includes a hit-point detector, e.g. a SITEK-detector, which may either be one-dimensional and placed vertically along the staff ST, or two-dimen¬ sional. The receiver unit M may be mounted so as to be oveable along the staff ST, thereby enabling the opera- tor T to place the staff in undulating or broken ground of all nature of severity, without the hit-point detec¬ tor needing to be excessively long. Naturally, a long hit-point indicator may also be used.

When the receiver unit M can be moved along the staff, the operator P will adjust the position of the receiver unit M on the staff until he sees on said unit a dash line deriving from the height-determining instrument. Although not shown, the hit-point indicator will have a special marking which is brought into alignment with the visible dash line by the operator. As will be under¬ stood, a detector hit can also be established with the aid of an indication from the electronics which receive the output signal from the hit-point detector. This latter alternative is particularly useful when the light dash would not be seen clearly because of poor contrast, e.g. when the measuring process is carried out in strong sunlight.

The position of the receiver unit along the staff is therefore detected with the aid of some suitable technique, for instance by optically reading a mark sensing along the staff or the like, and storing the result in the memory of an electronic calculating unit, as described herebelow.

The receiver unit M needs no particular receiver optics for focusing the received beam onto the hit-point posi¬ tion detector, since the laser beam will be sharply defined at the small distances concerned in this parti- cular case. On the other hand, it is preferred to filter incoming light prior to the light meeting the hit-point detector, so as to filter-out the two wavelengths emit¬ ted by the height-determining instrument.

The receiver unit M incorporates electronics which calculate a correction factor on the basis of the dif¬ ference between the hit-points in the direction-detector arrangement and also calculate the height which the beam would have had if it had not been deflected or bent, and mark this height on an indicator IND placed along the staff ST. The indicator may, for instance, include a row of light-emitting diodes, of which the one that is located at the calculated height is illuminated by the electronics in the receiver unit M. Alternatively, a row of light-emitting diodes can be illuminated up to the diode positioned at the calculated height. It will be understood that other types of indicators for marking the calculated, corrected height are also conceivable, such as an elongated liquid-crystal indicator, or the like.

It will also be understood that the various units illus¬ trated in Figure 1 may be positioned differently to that shown.

Figure 2A illustrates schematically an embodiment of the height-detecting device and the beam path to and in said device. Two light beams Lfl and Lf2 of completely different characters are emitted from a height determin¬ ing instrument 1. One of the light beams, Lfl, may have a wavelength of 900 n and the other, Lf2, a wavelength of 450 nm. These wavelengths are appropriate, since 450 nm lines lies within the visible wavelength range and 900 nm is twice this wavelength.

In the case of the illustrated embodiment, the light beams may be either spread over a stationary light plane around the height-determining instrument and may flash, e.g., in counterphase to one another or have different flashing characters or flashing frequencies, so as to enable them to be identified, or the beams may rotate and arrive at the detector sequentially, one after the other. In this latter case, the two light beams may be relatively close to one another followed by a long interspace or delay.

The light beams are emitted in mutually the same direc¬ tion but obtain mutually different curved paths as they pass through the atmosphere D which, because it is located above an area of ground that emits heat, will have a varying temperature index in the vertical direc¬ tion. The optical/electronic receiver M on the staff ST in Figure 1 is a hit-point detector 3 which gives the coordinates of the hit-point of a light spot on the detector in the form of an electric output signal. Only one conductor is shown between the detector and a signal processing circuit 6, although it will be understood that the signal may be transmitted on several conduc¬ tors, e.g. in the form of a digital signal.

In the illustrated case, the hit-point detector 3 is a surface detector, although it is also possible to use a linear detector since the temperature gradient of the air will often vary solely in one direction, the verti¬ cal direction. It is actually only the vertical direc¬ tion that is of interest when determining heights or when leveling. The SITEC-detector is one example of a detector which possesses these properties. This detector is available in both linear and two-dimensional vari¬ ants. Instead of a SITEC-detector, which operates in analog, the hit-point detector may have the form of a line of discrete, densely packed photo detectors ar¬ ranged along the staff. The positions of respective photo detectors in the receiver unit are accurately determined and thus the positions of the individual detectors on which the two beams from the height-deter- mining instrument impinge, or hit, will be known.

The rays in the two emitted light beams can be consid¬ ered approximately parallel, i.e. collimated. Since the refraction index of light in air is different at differ- ent wavelengths, the light which impinges on the hit- point indicator 3 having passed through air whose tem¬ perature is not homogenous and which varies transversely to the direction of the beam will be incident from different directions, due to being bent and will thus impinge on the detector 3 at the hit-point Tfl and Tf2 on the hit-point detector 3, these points being separat¬ ed from one another. The light points Tfl and Tf2 will also flutter and vary in size, owing to the fact that the air temperature gradients are not stable, but vary constantly.

A further problem encountered with the transmission of the emitted light beams is that stray light will con¬ stantly impair the signal/noise ratio at the receiver. The influence of stray light is reduced in the embodi¬ ment illustrated in Figure 2A with the aid of an optical bandpass filter 4 having two band passages, one for wavelengths around the wavelength of the one light beam Lfl and another for wavelengths around the wavelength of the other light beam Lf2. The bandpass filter 4 may, for- instance, be a two-peak filter, either in the form of a combined high-pass and low-pass filter, or in the form of an interference-filter. This will ensure that only light within the wavelength regions of the emitted light beams will be received by the receiver and therewith considerably reduce noise caused by background radia¬ tion.

The signal from the detector 3 for the hit-points of each light beam is sampled in a signal processing unit 6 at the times when respective light beams impinge on the detector. The unit 6 calculates the mean position of each focusing point, for instance by calculating the mean value of each of the hit-point values sampled.

Modulation is achieved by modulating the two signals, each representing a respective emitted light beam Lfl and Lf2 shifted in phase, e.g. in counterphase, so that they can be sampled individually and will not overlap at the sampling moment. Figure 2A illustrates a possibility of transferring pulse-pattern signals from the instru¬ ment 1 to the receiver unit 3, 4 with the aid of an additional radio transmitter 9 and radio receiver 10 for the synchronizing signals. The receiver 10 feeds the gained sync-signal to a sync-input on the signal pro- cessing unit 6.

The respective pulse patterns of the light beams can also be transferred by allowing one or the other of said light beams, or both of said beams, to have a different character at given time points, thereby to provide for synchronization of the circuits which detect the detec- tor output signal. This character is obtained from the hit-point detector and is transferred to the signal processing unit 6, together with the signal relating to the position on which the beam impinges on the detector, i.e. the hit-point position. The sync-signals can be formed directly by the signal processing unit 6.

Synchronization may, alternatively, also be effected with the aid of two crystal oscillators, one in the transmitter unit 9 on the instrument 1 and one in the receiver unit 10 on the staff ST (see Figure 1) , these oscillators working with the same frequency. The crystal oscillator on the staff is synchronized with the crystal oscillator on the instrument at different points in time, by phase-locking the oscillator on a sync-signal transmitted from the unit 9 to the unit 10. Alternative¬ ly, it may be possible to transmit the sync-signals directly from the unit 9 to the unit 10 without needing to provide the unit 10 with a steerable crystal oscilla- "tor. Furthermore, it is possible to transmit a particu¬ lar sync-signal to the hit-point detector instead of using separate sync-signal-transmitter/receiver. In this case, the sync-signal may, for instance, be a stronger light pulse than the information light pulses which indicate the hit-points.

The signal processing unit 6 mounted on the staff ST is preferably a computer and will use the information relating to the respective positions of the hit-points and the pulse having characteristics of the transmitted light beams to calculate a mean hit-point during several hit-point periods for each light beam. The computer also functions to calculate the height correction factor in accordance with the formulae given below. The signal from a height detector 7 which detects the position of the receiver unit M on the staff ST is fed to a separate input on the signal processing unit 6, which also func¬ tions to calculate the prevailing compensated height and a control signal is sent to a height indicator 8 which corresponds to the indicator IND in Figure 1.

Figure 2B is a flow diagram which illustrates one exem¬ plifying of the signal processing unit 6. It is believed that the flow diagram will be understood without being explained in detail.

However, for the sake of clarity, it is mentioned here that the phase positions for modulation of the light beams Lfl and Lf2 are marked in the case of a flashing laser plane. The pulsations of the two light beams may, for instance, be in counterphase, such that the one beam will shine for 60% of the time for instance, and the other for 40% of the time with pulsations of an informa¬ tive character, i.e. when no optional synchronizing pulse is transmitted. In the case of a rotating light beam, it is possible to omit sync-signals, since the frequency at which one rotating light lobe arrives can be detected by the received unit, thereby enabling the arrival of the other, rotating light lobe to be calcula¬ ted, since the phase positions of said lobes within a given period of rotation is always given. This calcula¬ tion can be carried out by the signal processing unit 6 and is well known to the person skilled in this art and need not therefore be described in detail.

If the frequency in laser plane modulation of the light beams Lfl and Lf2 is, e.g. l kHz with high precision, the receiver can be demodulated in the correct phase position for a number of seconds when using crystal oscillators in the absence of a transmitted sync-signal during this period. A high frequency accuracy can be maintained relatively easily. The deviation in the direction of respective received parts of the light beams Lfl and Lf2 that can be measured in accordance with the invention is a measure¬ ment of the total directional error to the target. It is assumed that the light beams Lfl and Lf2 pass through the same atmosphere. This is approximately true, since the deviation between light beams of two mutually dif¬ ferent colours, i.e. wavelengths, is often relatively small in comparison with the chang in the temperature gradient in the atmosphere through which the beams pass.

In the case of a height-determining unit which operates with a rotating light beam, it may be possible to place a separate detector (not shown) adjacent the hit-point detector, immediately upwards of said detector as seen in the direction of rotation. This separate detector will solely indicate hits by the different beams of mutually different character and send sync-pulses to the unit 6 which indicate hits by one of the other of the two beams Lfl and Lf2.

Figure 2C illustrates one embodiment of a circuit for distinguishing between the two hit-points in the case of a rotating light beam. One signal containing information of the occurrence of a hit by the two rotating light beams on the receiver unit M (see Figure 1) is sent to the input of a distribution circuit 15. The incoming signal is in the form of pulses formed by an amplifying and pulse-forming circuit 16, to which an analog hit- point signal has been delivered. Pulse forming may be effected, for instance, with the aid of a Sch itt- trigger (not shown) . The distribution circuit 15 has two outputs and divides the incoming pulse train such that each alternate pulse is sent to a respective one of the two outputs. When the light beams lie relatively close together, the distribution circuits 15 will preferably include an arrangement which functions to detect those parts of the incoming signal which have long pulse-interspacing in relation to those parts of the signal which have a short pulse-interspacing, so that after a long pulse-interspacing, a pulse can be safely applied to the one output and after a short pulse-inter¬ spacing, a pulse can be safely applied to the other of said inputs. Such circuits can be constructed in many different ways, all of which are well known to the skilled person and need not therefore be described here in detail.

A signal containing information concerning the position of a hit-point on the hit-point position detector 3 is fed to the input of two choppers, a first chopper 17 for the one hit-point Tfl and a second chopper 18 for the second hit-point Tf2. The first chopper 17 is controlled by the one output signal of the distribution circuit 15 such as to allow through solely information which re- lates to the hit-point y_._p.. from the detector 3 during a hit by the light beam Tfl. The second chopper 18 is controlled by the other output signal of the distribu¬ tion circuit 15 such as to allow through solely informa¬ tion which relates to the hit-point y_^-.,, from the detector 3 during a hit by the light beam Tf2. The output signals from the choppers 17 and 18 are each sent to a respective input on the calculating unit 19, which is also supplied with information concerning the height or vertical position of the receiver unit M on the staff ST. The calculating unit 19 calculates the correction height, corrects the detected height position and sends a control signal to an indicator 20 showing this corrected height position.

The embodiment illustrated in Figure 3 is particularly adapted for an embodiment which utilizes a stationary, non-flashing laser plane with two emitted light beams of mutually different wavelengths. In the Figure 3 embodi¬ ment, the filter 25 has the form of a disc which is rotated by a motor 26, the drive shaft of which is positioned roughly level with one edge of the hit-point detector 3 and the radius of which is at least equal to the length of the detector 3, so that one-half of the filter disc 25 will extend over the full limit of the space in which the light beams can pass in front of the detector 3.

Filter disc 25 will preferably include two semi-circular interference filters, each having a respective pass-band and each being positioned by the side of the other so as to form a circle. The pass-band of one of said interfer¬ ence filters will lie around the wavelength of the light beam Lfl and the other of said filters will lie around the wavelength of the light beam Lf2. When the filter rotates, the image point on the detector 3 will jump between the hit points Tfl and Tf2 of the two beams Lfl and Lf2, therewith providing amplitude modulation of the output signal from the detector 3. This signal is syn¬ chronously detected with the aid of a reference signal obtained from a reading fork (not shown) mounted on the edge of the filter disc, said reading fork providing information relating to the position of rotation of the filter disc. The synchronously detected output signal is filtered through a low-pass filter so as to obtain a mean value of the hit-point displacement. A similar circuit to that shown in Figure 2 C can be used to this end. In the illustrated case, however, the signals controlling the choppers 17 and 18 may have the form of two signals arriving directly from the motor 26.

In the case of the illustrated embodiment, the light beams may be continuous. Synchronization is effected 16 between detection of the signal detected by the detector 3 and rotation of the filter disc 10.

When the temperature To is 0°C, the air pressure Po is - 760 mmHg (101 kPa) , and the light beam has a wavelength λ, the following equation is obtained for the diffraction index n : g

(n -1)*10~⁸ = 2876.4 + 488.64/ λ ² + 6.8/λ⁴ (1) When λ = 900 nm, (n -1) = 293.74*10~⁶

9 -6

When λ = 450 nm_r (n -1) = 313.30*10 g

The refraction index is also dependent on air pressure P and temperature T in accordance with the following equation:

(n -!),_ _m = (n -l)*P/760*(273.2/(273.2+T)) g P,T g -₆

When λ = 900 nm, (n -1) = 105.6*10 *P/(273.2+T) g P.T -₆

When λ - 450 nm, (n -1) = 112.6*10 *P/(273.2+T) g P,T

A temperature gradient which varies perpendicularly to the direction of a light beam will cause the beam to bend. We assume that the temperature gradient is α °C/_tι. The angular change can be calculated with the guidance of the figures shown schematically in Figure 4A. Posi¬ tioning of the height-determining instrument is marked x. Bending of the beam around a circular arc having radius R at a temperature Tl and around a circular arc of radius R-d at a temperature T1+5T. There is then obtained:

R*7 = D

R*7 = (R-d)*7 = α*d*(dn /dT)*D y Solving of these equations gives: 7 = α* (dn /dT) *D

-6 -6

7 = α*D*l.0752*10 and y = α*D*l.1468*10

at a temperature of 0°C and a pressure of 760 mmHg. This gives:

7₂/7_ι = 1.066

This shows that the angular deviation is about 6.6% higher at λ = 450 nm than at λ ^*= 900 nm.

Figure 4B shows the height-determining instrument placed ^* at x and the hit-point detector placed at 3'. The deviation from a straight beam path along the line E for the beam L takes place around a circular arc of radius

R and its centre in C , while the deviation for the

1 1 beam L takes place around a circular arc of radius R 2 ^ 2 with its centre in C . K shows the correction that must

2 be made from the point of impingement, hit-point, of the beam L . The following equations can be constructed.

R *7 = D

1 'l = α*(dn /dT) ; *D

1 1 R *7 = D

2 2

7 = α*(dn /dT) *D ^•2 g 2

δ = R -R -(R -R )*cos7 = (R -R )*(l-cos7, ) 1 2 1 2 ^J ' l 1 2 ' ' l ' K = R *(l-coε7„ )

1 '1 K/δ = R₁/ (R₁-R₂) = 7₂/ γ₂-_7ι) = 1. 1468/ (1. 1468- 1.0752) = 16

when λ = 900 nm and λ„ = 450 nm. 1 2

This shows that the correction to be made is 16 times the distance between the hit-points on the hit-point indicator.

In the case of short distances between the instrument and the target, the deviation between the paths followed by the light beams Lfl and Lf2 will be small, and thus the accuracy to which any correction must be made will also be small, while in the case of longer distances, the deviation between the paths will be greater and the correction required must be calculated to a higher degree of accuracy. This is only natural, since bending of the beams due to light refraction phenomena is more pronounced when measuring over longer distances, where the need for correction is absolute.

It will be obvious that corrections can also be made in the horizontal plane, i.e. for bending of the beam in said plane with the aid of a two-dimensional hit-point detector. Such a detector can be used when indicating the direction of the beam path in the horizontal plane and also indicating the horizontal angular position of the staff ST in relation to the height-determining instrument. The correction is then made in accordance with the calculating principles described above with reference to corrections in the vertical plane.

Claims

1. A height-determining arrangement with compensation for errors in height due to curved beam paths when determining heights with the aid of a height-determining instrument (1) and a height-detecting arrangement (ST) which receives light transmitted in a horizontal plane from the height-determining instrument, c h a r a c - t e r i z e d in that the height-determining instrument is intended to transmit light within at least two, mutually different and narrow wavelength ranges and that the height-detecting arrangement (ST) includes a light- receiving unit which indicates hit-points on height levels of the light emitted by the height-determining instrument (1) in said wavelength ranges; in that a calculating unit (6; Figure 2B; 19) is coupled to the receiving arrangement and functions to calculate a correction factor on the basis of the difference between the indicated hit-points and also functions to calculate the height that the emitted light beam would have if not bent, on the basis of the height of the indicated hit and the calculated correction factor, and presents the calculated height on an indicating unit (IND) on the height detecting arrangement.

2. An arrangement which includes a height-determining instrument from which light is emitted in a rotating, horizontal plane, in accordance with Figure 1, c h a r a c t e r i z e d in that the height-determin¬ ing instrument is intended to emit at least two light beams which follow one another sequentially in said rotational path, wherein each said light beam has one of said narrow wavelength ranges. 3. An arrangement according to Claim 2, c h a r a c ¬ t e r i z e d by a device (9) on the height-determining instrument which functions to detect the rotational positions of the emitted light beams and to send in- formation relating to said rotational positions to a receiver (10) on the height-detecting unit (ST) ; in that the receiver is intended to send the received rotational position information to the calculating unit, which, when light hits the light receiving unit of the height- detecting unit, calculates on the basis of said informa¬ tion which of said light beams has hit said receiver unit.

4. An arrangement according to any one of the preced- ing Claims, c h a r a c t e r i z e d in that the light-receiver unit includes a hit-point indicating detector (3) for detecting light (Lfl, Lf2) emitted by the height-determining instrument and hitting said detector.

5. An arrangement according to Claim 4, c h a r a c ¬ t e r i z e d in that the light-receiver unit also includes an optical filter device (4; 25) which has pass-bands for the wavelength regions of respective light beams.

6. An arrangement according to Claim 5, c h a r a c ¬ t e r i z e d in that the optical filter device is an optical peak filter having a respective band-passageway for wavelengths in the region of the wavelength regions of said emitted light.

7. An arrangement according to Claim 5, c h a r a c ¬ t e r i z e d in that the optical filter device in- eludes a rotating filter comprising a disc (25) divided into sections, wherein each section has a pass-band which allows the wavelength of one of the emitted light beams to pass through.

8. An arrangement according to any one of the preced- ing Claims, c h a r a c t e r i z e d in that the height-determining instrument includes a transmitter diode for each of the wavelength regions of the emitted light.

9. An arrangement according to any one of the preced¬ ing Claims, c h a r a c t e r i z e d in that the height-determining instrument is intended to emit pul¬ sated light of mutually different phase positions for the different light wavelengths, so that light of said different wavelength regions will not be emitted simul¬ taneously.

10. An arrangement according to Claim 9, c h a r a c ¬ t e r i z e d in that the light pulses of different wavelengths have mutually different characters.

AMENDED CLAIMS

[received by the International Bureau on 25 September 1992 (25.09.92); original claim 1 amended; remaining claims unchanged (1 page)]

tion for errors in height due to curved beam paths when determining heights with the aid of a height- determining instrument (1) and a height-detecting arrangement (ST) which receives light transmitted in a horizontal plane from the height-determining instru¬ ment, the height-determining instrument being adapted to transmit light within at least two, mutually different and narrow wavelength ranges and the height- detecting arrangement (ST) including a light-receiving unit which indicates hit-points on height levels of the light emitted by the height-determining instrument (1) in said wavelength ranges, c h a r a c t e r ¬ i z e d in that a calculating unit (6; Figure 2B; 19) is coupled to the receiving arrangement and functions to calculate a correction factor on the basis of the difference between the indicated hit-points and also functions to calculate the height that the emitted light beam would have if not bent, on the basis of the height of the indicated hit and the calculated cor¬ rection factor, and presents the calculated height on an indicating unit (IND) on the height-detecting arrangement.

2. An arrangement which includes a height-deter¬ mining instrument from which light is emitted in a rotating, horizontal plane, in accordance with Figure 1, c h a r a c t e r i z e d in that the height-determining instrument is intended to emit at least two light beams which follow one another sequentially in said rotational path, wherein each said light beam has one of said narrow wavelength ranges, STATEMENT UNDER ARTICLE 19

The new Cl 1 has the following amendments to the earlier Claim 1:

The word "c h a r a c t e r i z e d" has been moved to line 16, after "wavelength ranges", the expression "in that" on line 10 has been canceled, the expression "is intended" on line 11 has been changed into "being adapted", and the word "includes" has been changed into "including".