Electromagnetic profile scanner

In a method of measuring a selected surface of an object at a distance, of the type wherein electromagnetic radiation having a structured pattern is projected from a first predetermined location over a predetermined angular range onto the selected surface of the object;

• electromagnetic radiation reflected from the selected surface of the object is received at a second predetermined location differing from the first predetermined location, and the directional distribution of the received electromagnetic radiation is measured;
• whereby the coordinates of portions of the selected surface are calculated, permitting the surface profile of the selected surface to be simulated;
• the improvement comprising:
• (a) projecting from a first predetermined location over a predetermined angular range onto the selected surface of the object a single structured pattern of electromagnetic radiation comprising an array of spatially arranged pattern elements selected from at least two mutually distinguishable types, where each pattern element comprises at least a first and a second discrete physical characteristic, each discrete physical characteristic being associated with a discrete type of information, said pattern being selected so that any portion of the pattern of at least some preselected minimum size is distinguishable from any other portion of the pattern;
• (b) receiving at a second predetermined location differing from the first predetermined location electromagnetic radiation reflected from the selected surface of the object and measuring over a scan of the object a preselected parameter of the reflected radiation for discriminating between pattern elements of the electromagnetic radiation originating from the projected pattern and reflected from the selected surface of the object;
• (c) converting the received electromagnetic radiation into data representing the distribution over a scan of said preselected parameter associated with an image of the reflection of at least a portion of the projected pattern reflected from the selected surface of the object;
• (d) using the data obtained in step (c), comparing the scan distribution data associated with the image of the reflection with data representing the projected pattern, so as to match identifiable portions of the image with corresponding portions of the projected pattern;
• whereby the coordinates of the locations on the surface of the object on which each identifiable portion of the projected pattern fell are correlated with the matched data obtained from step (d).

A method of measuring a surface portion of an object at a distance, comprising the steps of:

• (a) illuminating the object from a first predetermined location over a predetermined angular range with a single projected thin generally fan-shaped beam of electromagnetic radiation that spatially varies along its wider dimension in a pattern comprising a spatially arranged sequence of pattern elements of at least two mutually distinguishable types, where each pattern element comprises at least a first and a second discrete physical characteristic, each discrete physical characteristic being associated with a discrete type of information, said pattern being selected so that any portion of the pattern of at least some preselected minimum size is distinguishable from any other portion of the pattern;
• (b) detecting electromagnetic radiation reflected from the surface portion of the object over a scan of the object;
• (c) converting the detected electromagnetic radiation into data representing the distribution over a scan of a preselected parameter of the reflected radiation associated with an image of the reflection of at least a portion of the projected pattern reflected from the object;
• (d) correlating each such distinguishable portion of the projected pattern with the reflection data obtained from step (c) by comparing data representing the pattern of the illuminating beam with the said reflection data, so as to establish a match of an identifiable portion of the reflected radiation and a corresponding portion of the illuminating beam whereby the portion of the surface of the object from which the reflected radiation has been reflected is ascertained;
• and
• (e) computing distance data for a scan of the object and coordinating said distance data with the matched reflected radiation data, thereby generating profile data representing the profile of at least a portion of the scanned object.

A method of measuring a selected surface of an object at a distance, comprising the steps of:

• (a) projecting from a first predetermined location over a predetermined angular range onto the selected surface of the object a single pattern of electromagnetic radiation comprising an array of spatially arranged pattern elements of at least two mutually distinguishable types, where each pattern element comprises at least two contrasting pattern element segments, each of at least two selected ones of said segments representing information of a discrete type;
• said pattern being selected so that any portion of the pattern of at least some preselected minimum size is distinguishable from any other portion of the pattern;
• (b) receiving at a second predetermined location differing from the first predetermined location radiation reflected from the selected surface of the object and measuring (i) the directional distribution of the radiation over a scan of the object and (ii) a preselected parameter of the reflected radiation whose variable value over the scan is measured, said preselected parameter being selected for discriminating between and identifying pattern elements and their types within reflection data derived from radiation originating from the projected pattern and reflected from the selected surface of the object;
• (c) the received radiation into data representing an image of the reflection of at least a portion of the projected pattern reflected from the selected surface of the object;
• (d) using the data obtained in step (c), comparing the data representing the image of the reflection with data representing the projected pattern, so as to match identifiable portions of the image with the corresponding portions of the projected pattern;
• and
• (e) calculating the spatial coordinates of the locations on the surface of the object on which each identifiable portion of the projected pattern fell from data representing (i) the first and second predetermined locations, (ii) the known directions of projection for each portion of the projected pattern matched in step (d), and (iii) measured directions pursuant to step (b), from which each corresponding portion of the image was received.

Apparatus for measuring a surface portion of an object at a distance, comprising:

• (a) an illuminator for illuminating the object by projecting from a first predetermined location over a predetermined angular range onto the surface portion of the object an illuminating beam comprising a single spatially varied pattern of electromagnetic radiation selected so that any portion of the pattern of at least some preselected minimum size is distinguishable from any other portion of the pattern, said pattern comprised of an array of spatially arranged pattern elements of at least two mutually distinguishable types, where each pattern element comprises at least a first and a second discrete physical characteristic, each discrete physical characteristic being associated with a discrete type of information;
• (b) a detector for receiving electromagnetic radiation reflected from the surface portion of the object;
• (c) a converter for converting the received electromagnetic radiation into computer-readable digital reflection data;
• (d) a discriminator for processing said data for correlating each said distinguishable portion of the projected pattern with the image of its reflection by comparing transmission data representing the pattern of the illuminating beam with the reflection data, so as to establish a match of an identifiable portion of the reflected radiation and a corresponding portion of the illuminating beam, whereby the portion of the surface of the object from which the reflected radiation has been reflected is ascertained;
• (e) a coordinate calculator for computing the spatial coordinates of the portion of that surface of the object on which each distinguishable portion of the pattern falls;
• and
• (f) a profile generator for computing and generating distance data correlated with the computed spatial coordinates of the scanned object thereby to generate data representing the profile of at least a portion of the scanned object.

Apparatus for measuring the spatial coordinates of a selected portion of the surface of an object to be measured, comprising:

• a laser source;
• a cylindrical lens receiving light from the laser source and generating a fan-shaped beam of light;
• a mask formed as a pattern comprising a spatially ordered array of pattern elements each including a transparent region followed by an opaque region selected so that each pattern element is identifiable as being of a selected one of at least two types of pattern elements mutually distinguishable from one another by means of the ratio in spatial extent of the transparent and opaque regions therein;
• said pattern being selected so that any portion of the pattern of at least some preselected minimum size is distinguishable from any other portion of the pattern;
• said laser source, cylindrical lens and mask being spatially disposed to project the pattern of the mask onto the selected surface of the object to be measured;
• an image sensor having a generally linear array of sensing elements lying generally in the plane of the fan-shaped beam of light, for receiving light reflected from the object to be measured;
• said image sensor generating an electronic signal whose amplitude varies over the linear array of sensing elements in accordance with the variation in space of the intensity of the light reflected from the object and received by the image sensor;
• a converter for converting the electronic signal produced by the image sensor into computer-readable digital reflection data;
• means for identifying within the reflection data information representative of a reflection sequence of pattern elements of the projected pattern;
• means for comparing the reflection sequence of pattern elements with each projected sequence of pattern elements of the mask of a sequence length equal to the length of the reflection sequence;
• whereby the image data may be correlated with a discrete identified portion of the surface of the object being measured;
• and
• using the principle of triangulation, determining the angles of incidence and reflection of light projected upon and reflected from the selected surface of the object being measured, and using the known geometry of said apparatus including the laser and image sensor thereby to compute the spatial coordinates of the identified portion of the surface of the object;
• whereby the spatial coordinates thus computed are correlated uniquely with the pattern projected onto the surface, thereby to generate reliable spatial coordinate information of the identified portion of the surface of the object being measured.

Apparatus for measuring a selected surface of an object at a distance comprising

• a laser source;
• a cylindrical lens through which light from the laser source passes thereby to form a fan-shaped beam of light;
• a first mirror for reflecting the fan-shaped beam of light toward the selected surface of the object to be measured;
• a mask interposed between the first mirror and the object to be measured and having thereon and superimposing upon the fan-shaped beam of light a single pattern comprised of an array of sequential pattern elements;
• each pattern element being a selected one of at least two pattern element types each including a transparent region followed by an opaque region, said pattern elements mutually distinguishable from one another by means of the ratio in spatial extent of the transparent and opaque regions therein;
• said pattern being selected so that any portion of the pattern of at least some preselected minimum size is distinguishable from any other portion of the pattern;
• a second mirror for receiving light reflected from the selected surface of the object;
• an image lens for focusing light reflected from the second mirror;
• an image sensor having a generally linear array of sensing elements lying generally in the plane of the fan-shaped beam of light;
• said image sensor receiving light reflected from the second mirror that is passed through the image lens;
• said image sensor being located relative to the second mirror and image lens to receive a focused image of light reflected from the selected surface of the object;
• said image sensor generating a received signal whose magnitude over the linear array of sensing elements is proportional to the intensity of the light reflected from the selected surface of the object from one extremity of the selected surface to the other over a scan;
• a converter for converting the received signal produced by the image sensor to computer-readable digital reflection data in a sequence correlatable with the sequence of variation of magnitude of the received signal;
• pattern element identification means for identifying within said reflection data information representing a sequence of pattern elements of the reflected pattern emanating from the selected surface of the object to be measured;
• comparison means for comparing the identified series of pattern elements in the reflection data with each sequence of pattern elements in the transmitted data of sequence length equal to the length of the sequence of reflected pattern element data;
• means for matching the apparent sequence of pattern elements in the reflection data to the projected pattern element data to obtain the best match of reflected pattern element data with the transmitted sequence of pattern elements thereby to correlate the reflection data with an identified portion of the object being measured;
• means for computing for each intercept of a pattern element with the selected surface of the object being measured the spatial coordinates of that intercept, using the principal of triangulation, measured angles of incidence and reflection of the projected and reflected patterns, and the known geometry of the apparatus including the mirrors, lenses, laser source, and image sensor;
• thereby to derive data representing the spatial coordinates of the identifiable portion of the object to be measured.

Apparatus for measuring a selected surface of an object at a distance, comprising:

• (a) a projector for projecting from a first predetermined location over a predetermined angular range onto the selected surface of the object a single pattern of electromagnetic radiation comprising an array of spatially arranged pattern elements of at least two mutually distinguishable types, where each pattern element comprises at least a first and a second discrete physical characteristic, each discrete physical characteristic being associated with a discrete type of information, said pattern being selected so that any portion of the pattern of at least some preselected minimum size is distinguishable from any other portion of the pattern;
• (b) a detector for receiving at a second predetermined location differing from the first predetermined location radiation reflected from the selected surface of the object and measuring (i) the directional distribution of the radiation over a scan of the object and (ii) a preselected received parameter of the reflected radiation whose variable value over the scan is measured, said received parameter being selected for discriminating between and identifying pattern elements and their types within reflection data derived from radiation originating from the projected pattern and reflected from the selected surface of the object;
• (c) a converter for converting the received radiation into data representing an image of the reflection of at least a portion of the projected pattern reflected from the selected surface of the object;
• (d) a discriminator for comparing the data generated by the converter as representing the image of the reflection with data representing the projected pattern, so as to match identifiable portions of the image with the corresponding portions of the projected pattern;
• and
• (e) a coordinate calculator for calculating the spatial coordinates of the locations on the surface of the object on which each identifiable portion of the projected pattern fell, from data representing (i) the locations of the projector and detector, (ii) the known directions of projection for each portion of the projected pattern matched in the discriminator, and (iii) measured directions pursuant to those received by the detector, from which each corresponding portion of the image was received.

In or for use with apparatus for measuring a selected surface of an object at a distance, of the type having a projector for projecting electromagnetic radiation having a structured pattern from a first predetermined location over a predetermined angular range onto the selected surface of the object;

• a detector at a second predetermined location differing from the first predetermined location for receiving electromagnetic radiation reflected from the selected surface of the object, and measuring means for measuring the directional distribution of the received electromagnetic radiation;
• whereby the coordinates of portions of the selected surface are calculated, permitting the surface profile of the selected surface to be simulated;
• the improvement comprising:
• (a) a projector for projecting from a first predetermined location over a predetermined angular range onto the selected surface of the object a single structured pattern of electromagnetic radiation comprising spatially varied pattern elements of at least two mutually distinguishable types, where each pattern element comprises at least a first and a second discrete physical characteristic, each discrete physical characteristic being associated with a discrete type of information;
• said pattern being selected so that any portion of the pattern of at least some preselected minimum size is distinguishable from any other portion of the pattern;
• (b) a detector for detecting at a second predetermined location differing from the first predetermined location electromagnetic radiation reflected from the selected surface of the object and measuring over a scan of the object a preselected received parameter of the reflected radiation for discriminating between pattern elements of the electromagnetic radiation originating from the projected pattern and reflected from the selected surface of the object;
• (c) a converter for converting the detected electromagnetic radiation into data representing the distribution over a scan of said preselected received parameter of the reflected radiation associated with an image of the reflection of at least a portion of the projected pattern reflected from the selected surface of the object;
• (d) a discriminator for comparing the scan distribution data associated with the image of the reflection with data representing the projected pattern, so as to match identifiable portions of the image with the corresponding portions of the projected pattern;
• whereby the coordinates of the locations on the surface of the object on which each identifiable portion of the projected pattern fell are correlated with the matched data.

Apparatus for measuring a surface portion of an object at a distance, comprising:

• (a) an illuminator for illuminating the object by projecting from a first predetermined location over a predetermined angular range onto the surface portion of the object a single illuminating beam comprising a projected thin generally fan-shaped beam of electromagnetic radiation that spatially varies along its wider dimension in a pattern comprising a spatially arranged sequence of pattern elements of at least two mutually distinguishable types, where each pattern element comprises at least a first and a second discrete physical characteristic, each discrete physical characteristic being associated with a discrete type of information, said pattern being selected so that any portion of the pattern of at least some preselected minimum size is distinguishable from any other portion of the pattern;
• (b) a detector for receiving electromagnetic radiation reflected from the surface portion of the object over a scan of the object;
• (c) a converter for converting the received electromagnetic radiation into data representing the distribution over a scan of a preselected parameter of the reflected radiation associated with an image of the reflection of at least a portion of the projected pattern reflected from the surface portion of the object;
• (d) a discriminator for correlating each such distinguishable portion of the projected pattern with the reflection data generated by the converter by comparing data representing the pattern of the illuminating beam with the said reflection data, so as to establish a match of an identifiable portion of the reflected radiation and a corresponding portion of the illuminating beam whereby the portion of the surface of the object from which the reflected radiation has been reflected is ascertained;
• and
• (e) a profile generator for computing distance data for a scan of the object and coordinating said distance data with the matched reflected radiation data thereby generating profile data representing the profile of at least a portion of the scanned object.

In or for use in apparatus for measuring a selected surface of an object at a distance that includes:

• (a) a projector for projecting from a first predetermined location over a predetermined angular range onto the selected surface of the object a pattern of electromagnetic radiation;
• (b) a detector for receiving at a second predetermined location differing from the first predetermined location radiation reflected from the selected surface of the object and measuring radiation reflected from the object including the directional distribution of the electromagnetic radiation over a scan of the object;
• (c) a converter for converting the received electromagnetic radiation into data representing an image of the reflection of at least a portion of the projected pattern reflected from the selected surface of the object;
• and
• (d) a coordinate calculator for calculating the spatial coordinates of the locations on the surface of the object on which each identifiable portion of the projected pattern fell, from data representing (i) the locations of the projector and detector, (ii) the known directions of projection for each portion of the projected pattern, and (iii) measured directions from which the reflected radiation was received;
• the improvement comprising:
• (e) a projector for projecting from a first predetermined location over a predetermined angular range onto the selected surface of the object a single selected pattern of electromagnetic radiation comprising an array of spatially arranged pattern elements of at least two mutually distinguishable types, where each pattern element comprises at least a first and a second discrete physical characteristic, each discrete physical characteristic being associated with a discrete type of information, said pattern being selected so that any portion of the pattern of at least some preselected minimum size is distinguishable from any other portion of the pattern;
• and
• (f) a discriminator for comparing the data generated by the converter with data representing the projected pattern, so as to match identifiable portions of the image with the corresponding portions of the projected pattern, thereby to associate identifiable portions of the image and the measured radiation associated therewith with the spatial coordinates of the locations on the surface of the scanned object on which identifiable portions of the projected pattern fell.

Apparatus for measuring a selected surface of an object at a distance, comprising:

• (a) a projector for projecting from a first predetermined location over a predetermined angular range onto the selected surface of the object a single pattern of electromagnetic radiation comprising an array of spatially arranged pattern elements of at least two mutually distinguishable types, where each pattern element comprises at least a first and a second discrete physical characteristic, each discrete physical characteristic being associated with a discrete type of information, said pattern being selected so that any portion of the pattern of at least some preselected minimum size is distinguishable from any other portion of the pattern;
• (b) a detector for receiving at a second predetermined location differing from the first predetermined location electromagnetic radiation reflected from the selected surface of the object and measuring (i) the directional distribution of the electromagnetic radiation over a scan of the object and (ii) a preselected received parameter of the reflected radiation whose variable value over the scan is measured, said preselected received parameter being selected for discriminating between and identifying pattern elements and their types within reflection data derived from electromagnetic radiation originating from the projected pattern and reflected from the selected surface of the object;
• (c) a converter for converting the received electromagnetic radiation into data representing an image of the reflection of at least a portion of the projected pattern reflected from the selected surface of the object;
• (d) a discriminator for comparing the data generated by the converter with data representing the projected pattern, so as to match identifiable portions of the image with the corresponding portions of the projected pattern;
• and
• (e) a coordinate calculator for calculating the spatial coordinates of the locations on the surface of the object on which each identifiable portion of the projected pattern fell, from data representing (i) the locations of the projector and detector, (ii) the known directions of projection for each portion of the projected pattern matched in the discriminator, and (iii) measured directions pursuant to those received by the detector, from which each corresponding portion of the image was received.

In a method for unambiguously identifying the location of a point within the view of a two- or three-dimensional measurement sensor with a single projected pattern of electromagnetic radiation comprising the steps of:

• (a) projecting a binary pattern of radiation having unique codes over any span of N segments out of a total of as many as 2.sup.N segments onto a surface to be measured, so that said segments form uniquely identifiable local patterns;
• (b) recording reflected radiation with a detector and generating a recorded signal;
• (c) analyzing the recorded signal and providing a digital representation thereof;
• and
• (d) identifying the location of the point in the pattern by comparing the digital representation with a known reference pattern digital representation;
• the improvement comprising:
• selecting each segment to have a selected one of two mutually distinguishable spatial structures.

In a method of measuring a selected surface of an object at a distance that comprises the steps of projecting a pattern on the object, detecting and observing the reflection of that pattern, and correlating distance data for the selected surface of the object determined by triangulation with data representing elements of the reflected pattern or an identifiable portion thereof, and wherein some of the pattern data may be missing or contaminated;

• an improved method of pattern element recovery comprising:
• computing from apparently reliable observed reflection data the pattern trend of an identifiable portion of the reflected pattern;
• estimating the expected value of a selected parameter within the observed data associated with the next adjacent observed portion of the pattern outside the reliable data;
• testing the observed value of said parameter for the next adjacent observed portion of the pattern so as to assess the degree of correspondence between the observed and estimated expected values for such parameter at such next adjacent observed portion of the pattern;
• and
• accepting, rejecting, or relocating the position of the next adjacent observed portion of the pattern in dependence upon the degree of correspondence, and, where such next adjacent portion of the observed pattern is to be relocated, relocating data associated with said next adjacent portion to a position further away from the apparently reliable observed reflection data and inserting a parameter value for data located between the reliable data and the relocated data;
• so as to provide data representing an apparent continuity of the reflected pattern in correspondence with the transmitted pattern, as embodied in the reflected pattern data.

In or in combination with apparatus for measuring a selected surface of an object at a distance that includes a projector for projecting a pattern on the object, a receiver for detecting and observing the reflection of that pattern, a correlator for correlating distance data for the selected surface of the object determined by triangulation with data representing elements of the reflected pattern or an identifiable portion thereof, and wherein some of the pattern data may be missing or contaminated;

• pattern element recovery apparatus comprising:
• means for computing from apparently reliable observed reflection data the pattern trend of an identifiable portion of the reflected pattern;
• means for estimating the expected value of a selected parameter within the observed data associated with the next adjacent observed portion of the pattern outside the reliable data;
• means for testing the observed value of said parameter for the next adjacent observed portion of the pattern so as to assess the degree of correspondence between the observed and estimated expected values for such parameter at such next adjacent observed portion of the pattern;
• and
• means for accepting, rejecting, or relocating the position of the next adjacent observed portion of the pattern in dependence upon the degree of correspondence, and, where such next adjacent portion of the observed pattern is to be relocated, relocating data associated with said next adjacent portion to a position further away from the apparently reliable observed reflection data and inserting a parameter value for data located between the reliable data and the relocated data;
• so as to provide data representing an apparent continuity of the reflected pattern in correspondence with the transmitted pattern, as embodied in the reflected pattern data.

In a method of measuring a selected surface of an object at a distance that comprises the steps of projecting a pattern on the object, such pattern being comprised of pattern elements of substantially uniform width but having variable-width bright marks of at least two mutually distinguishable mark widths, and detecting the reflection of that pattern to generate observed reflection data representative of an observed sequence of pattern elements corresponding to a valid sequence of transmitted pattern elements within the pattern, so as to correlate distance data for the selected surface of the object determined by triangulation with received pattern element data;

• and wherein some of the observed reflection data may be missing or contaminated;
• a method of pattern element recovery for validating a sequence of pattern elements represented by corrected reflection data comprising:
• computing from reflection data accepted as reliable data the trend of the reflected pattern in the reflection data;
• estimating the expected sequence number in the sequence of pattern elements for the next observed data outside the reliable data for that pattern element apparently next in sequence in said trend so as to assess the degree of correspondence between the observed and estimated sequence numbers;
• and
• accepting, rejecting, or offsetting the data associated with the pattern element apparently next in sequence in the trend in dependence upon the degree of correspondence, and, where such observed pattern element position is to be offset, relocating such pattern element to a position further away from the sequence of positions in the established pattern trend, and inserting data corresponding to a contrived pattern element between the established trend and the offset pattern elements;
• so as to provide data representing an apparent continuity of the reflected pattern data in correspondence with the transmitted pattern.

In or in combination with apparatus for measuring a selected surface of an object at a distance that includes a projector for projecting a pattern on the object, such pattern being comprised of pattern elements of substantially uniform width but having variable-width bright marks of at least two mutually distinguishable mark widths, a receiver for detecting the reflection of that pattern to generate observed reflection data representative of an observed sequence of pattern elements corresponding to a valid sequence of transmitted pattern elements within the pattern, a correlator for correlating distance data for the selected surface of the object determined by triangulation with the observed sequence of pattern elements;

• and wherein some of the expected observed reflection data may be missing or contaminated;
• pattern element recovery apparatus for validating a sequence of pattern elements represented by corrected reflection data comprising:
• means for computing from reflection data accepted as reliable data the trend of the reflected pattern in the reflection data;
• means for estimating the expected sequence number in the sequence of pattern elements for the next observed data outside the reliable data for that pattern element apparently next in sequence in said trend so as to assess the degree of correspondence between the observed and estimated sequence numbers;
• and
• means for accepting, rejecting, or offsetting the data associated with the pattern element apparently next in sequence in the trend in dependence upon the degree of correspondence, and, where such observed pattern element position is to be offset, relocating such pattern element to a position further away from the sequence of positions in the established pattern trend, and inserting data corresponding to a contrived pattern element between the established trend and the offset pattern elements;
• so as to provide data representing an apparent continuity of the reflected pattern data in correspondence with the transmitted pattern.

In or in combination use with apparatus for measuring a selected surface of an object at a distance that comprises means for projecting a pattern of electromagnetic radiation on the object, means for detecting and observing the reflection of that pattern, means for correlating distance data for the selected surface of the object with spatial coordinates on that surface determined by triangulation with data representing elements of the reflected pattern or an identifiable portion thereof, and wherein some of the pattern data may be missing or contaminated;

• pattern element recovery apparatus comprising:
• means for computing from apparently reliable observed reflection data the pattern trend of an identifiable portion of the reflected pattern;
• means for estimating the expected value of a selected parameter within the observed data associated with the next adjacent observed portion of the pattern outside the reliable data;
• means for testing the observed value of said parameter for the next adjacent observed portion of the pattern so as to assess the degree of correspondence between the observed and estimated expected values for such parameter at such next adjacent observed portion of the pattern;
• and
• means for accepting, rejecting, or relocating the position of the next adjacent observed portion of the pattern in dependence upon the degree of correspondence, and, where such next adjacent portion of the observed pattern is to be relocated, relocating data associated with said next adjacent portion to a position further away from the apparently reliable observed reflection data and inserting a parameter value for data located between the reliable data and the relocated data;
• so as to provide a data signal representing an apparent continuity of the reflected pattern in correspondence with the transmitted pattern, as embodied in the reflected pattern data.

In or in combination with apparatus for measuring a selected surface of an object at a distance that comprises means for projecting a pattern of electromagnetic radiation on the object, such pattern being comprised of pattern elements of substantially uniform width but having variable-width bright marks of at least two mutually distinguishable mark widths, means for detecting the reflection of that pattern to generate observed reflection data representative of an observed sequence of pattern elements corresponding to a valid sequence of transmitted pattern elements within the pattern, and means for correlating distance data for the selected surface of the object with spatial coordinates on that surface determined by triangulation and wherein some of the expected observed reflection data may be missing or contaminated;

• pattern element recovery apparatus for validating a sequence of pattern elements represented by corrected reflection data comprising:
• means for computing from reflection data accepted as reliable data the trend of the reflected pattern in the reflection data;
• means for estimating the expected sequence number in the sequence of pattern elements for the next observed data outside the reliable data for that pattern element apparently next in sequence in said trend so as to assess the degree of correspondence between the observed and estimated sequence numbers;
• and
• means for accepting, rejecting, or offsetting the data associated with the pattern element apparently next in sequence in the trend in dependence upon the degree of correspondence, and, where such observed pattern element position is to be offset, relocating such pattern element to a position further away from the sequence of positions in the established pattern trend, and inserting data corresponding to a contrived pattern element between the established trend and the offset pattern elements;
• so as to provide a data signal representing an apparent continuity of the reflected pattern data in correspondence with the transmitted pattern.