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WO1992019935A1 - Dispositif de compensation pour niveau de hauteur - Google Patents

Dispositif de compensation pour niveau de hauteur Download PDF

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Publication number
WO1992019935A1
WO1992019935A1 PCT/SE1992/000296 SE9200296W WO9219935A1 WO 1992019935 A1 WO1992019935 A1 WO 1992019935A1 SE 9200296 W SE9200296 W SE 9200296W WO 9219935 A1 WO9219935 A1 WO 9219935A1
Authority
WO
WIPO (PCT)
Prior art keywords
height
light
hit
arrangement
emitted
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/SE1992/000296
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English (en)
Inventor
Rudolf Wiklund
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Geotronics AB
Original Assignee
Geotronics AB
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Geotronics AB filed Critical Geotronics AB
Publication of WO1992019935A1 publication Critical patent/WO1992019935A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C15/00—Surveying instruments or accessories not provided for in groups G01C1/00 - G01C13/00
    • G01C15/002—Active optical surveying means

Definitions

  • 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.
  • 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 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.
  • 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.
  • 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.
  • 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.
  • 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 actual height-determin ⁇ ing instrument itself transmits light within at least two, mutually different narrow wavelength regions
  • 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.
  • Figure 1 illustrates measuring equipment with a slightly exaggerated beam path between a height-determining instrument and a re ⁇ DCver, 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 ⁇ DC unit in accordance with the inven ⁇ tion, this embodiment being intended par ⁇ ticularly for generating a stationary light-plane from a height-determining instrument;
  • FIGS 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.
  • FIG. 1 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.
  • 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.
  • the refraction index will vary and the beam S will be deflected upwards.
  • 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.
  • 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.
  • a long hit-point indicator may also be used.
  • the operator P 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.
  • the hit-point indicator will have a special marking which is brought into alignment with the visible dash line by the operator.
  • 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.
  • 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.
  • FIG. 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • FIG. 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.
  • 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.
  • 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.
  • 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.
  • 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 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.
  • 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.
  • the signals controlling the choppers 17 and 18 may have the form of two signals arriving directly from the motor 26.
  • 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.
  • the refraction index is also dependent on air pressure P and temperature T in accordance with the following equation:
  • a temperature gradient which varies perpendicularly to the direction of a light beam will cause the beam to bend.
  • the temperature gradient is ⁇ °C/_t ⁇ .
  • 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:
  • 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
  • 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.
  • 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.

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  • Length Measuring Devices By Optical Means (AREA)
  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)

Abstract

L'invention concerne un dispositif permettant de compenser les erreurs de mesure dues à la courbure du faisceau lumineux lorsque l'on mesure des hauteurs à l'aide d'une lumière émise par un niveau de hauteur fixe (H) sur un dispositif de détection de hauteur (ST). L'unité d'émission de lumière du niveau de hauteur (H) émet au moins deux faisceaux de lumière, chacun d'eux étant caractérisé par une longueur d'onde étroite différente. Le dispositif de détection de hauteur (ST) comprend une unité de réception de lumière qui indique les points d'impact lumineux verticaux émis par l'instrument déterminant la hauteur (1) dans lesdites longueurs d'onde. Une unité calcule un facteur de correction à partir de la différence qui existe entre les points d'impact indiqués et calcule également la hauteur qu'aurait atteint la lumière émise en l'absence d'incurvation, à partir de la hauteur du point d'impact indiqué et à partir du facteur de correction et présente la hauteur calculée sur un dispositif indicateur (IND).
PCT/SE1992/000296 1991-05-08 1992-05-07 Dispositif de compensation pour niveau de hauteur Ceased WO1992019935A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE9101398-7 1991-05-08
SE9101398A SE9101398D0 (sv) 1991-05-08 1991-05-08 Kompensationsanordning foer hoejdavstaemnings- instrument

Publications (1)

Publication Number Publication Date
WO1992019935A1 true WO1992019935A1 (fr) 1992-11-12

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PCT/SE1992/000296 Ceased WO1992019935A1 (fr) 1991-05-08 1992-05-07 Dispositif de compensation pour niveau de hauteur

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WO (1) WO1992019935A1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2000767A3 (fr) * 2007-06-08 2010-02-24 Kabushiki Kaisha Topcon Système de mesure d'angle
US7908041B2 (en) 2004-04-29 2011-03-15 Munro & Associates, Inc. Self-leveling laser horizon for navigation guidance
US7983694B2 (en) 2004-02-17 2011-07-19 Nav-Track, Inc. Target and base station for a navigation system
US8214147B2 (en) 2007-03-21 2012-07-03 Nav-Track, Inc. Navigation unit and base station

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3446559A (en) * 1966-02-09 1969-05-27 Barnes Eng Co Instrument to correct survey errors caused by atmospheric refraction
US3606548A (en) * 1967-10-16 1971-09-20 Nat Res Dev Measurement of dispersion of light
US3915574A (en) * 1974-09-26 1975-10-28 Rca Corp Method for determining an accurate alignment of a laser beam
DE2726649B2 (de) * 1977-06-14 1979-10-18 Tammo Dr.-Ing. 3000 Hannover Glissmann Vorrichtung zur Richtungsmessung
DE3130747C1 (de) * 1981-08-04 1983-02-24 Dornier System Gmbh, 7990 Friedrichshafen Verfahren und Vorrichtung zur Bestimmung der Koordinaten des fiktiven Auftreffpunktes von ungebrochenen Lichtstrahlen
CH674080A5 (fr) * 1987-05-19 1990-04-30 Wild Leitz Ag

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3446559A (en) * 1966-02-09 1969-05-27 Barnes Eng Co Instrument to correct survey errors caused by atmospheric refraction
US3606548A (en) * 1967-10-16 1971-09-20 Nat Res Dev Measurement of dispersion of light
US3915574A (en) * 1974-09-26 1975-10-28 Rca Corp Method for determining an accurate alignment of a laser beam
DE2726649B2 (de) * 1977-06-14 1979-10-18 Tammo Dr.-Ing. 3000 Hannover Glissmann Vorrichtung zur Richtungsmessung
DE3130747C1 (de) * 1981-08-04 1983-02-24 Dornier System Gmbh, 7990 Friedrichshafen Verfahren und Vorrichtung zur Bestimmung der Koordinaten des fiktiven Auftreffpunktes von ungebrochenen Lichtstrahlen
CH674080A5 (fr) * 1987-05-19 1990-04-30 Wild Leitz Ag

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7983694B2 (en) 2004-02-17 2011-07-19 Nav-Track, Inc. Target and base station for a navigation system
US8010133B2 (en) 2004-02-17 2011-08-30 Nav-Track, Inc. Navigation system
US7908041B2 (en) 2004-04-29 2011-03-15 Munro & Associates, Inc. Self-leveling laser horizon for navigation guidance
US8214147B2 (en) 2007-03-21 2012-07-03 Nav-Track, Inc. Navigation unit and base station
EP2000767A3 (fr) * 2007-06-08 2010-02-24 Kabushiki Kaisha Topcon Système de mesure d'angle

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122 Ep: pct application non-entry in european phase