An overview of the advantages and constraints of coded pattern projection techniques for autonomous navigation
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paper_title: Determining surface orientation by projecting a stripe pattern

paper_content:

A method is presented for determining the surface orientations of an object by projecting a stripe pattern on to it. Assuming orthographical projection as a camera model and parallel light projection of the stripe pattern, the method obtains a 2 1/2-D representation of objects by estimating surface normals from the slopes and intervals of the stripes in the image. The 2 1/2-D image is further divided into planar or singly curved surfaces by examining the distribution of the surface normals in gradient space. A simple application to finding a planar surface and determining its orientation and shape is shown. The error in surface orientation is discussed. >
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paper_title: Structured light patterns for robot mobility

paper_content:

The authors describe some of the important operational considerations and image processing tasks required to utilize a nonscanning structured-light range sensor in path planning for robot mobility. The efforts have concentrated on the geometric design of the projectional grid with regard to smoothing of fine-scale range texture, and the development of image processing techniques in order to extract the deformed grid from the image. Particular emphasis is placed on the issues of operating in ambient lighting, smoothing of range texture, grid pattern selection, albedo normalization, grid extraction, and coarse registration of images to the projected grid. Once the grid is extracted, its global order allows intersections to be labeled, and disparities assigned and converted to range data. This range map can then be converted to a 'topography map' to be used for planning short-range paths through the environment while avoiding obstacles. >
---
paper_title: 3D reconstruction using an uncalibrated stereo pair of encoded images

paper_content:

The reconstruction of three dimensional (3-D) objects is used in CAD/CAM, robotics, remote sensing, etc. The models (images) can be either directly acquired by using special devices such as range finders, CTR scanners, etc. or they can be recovered from a series of 2-D images of the object. The authors report on a new method for reconstructing 3-D objects from two 2-D images using CCD cameras. This method uses a pseudo-random encoded grid projected on the object. The grid nodes are used in matching left to right 2-D images. The set of matched points are further used to calculate the disparity of each point of the object surface. Experimental examples illustrate the performance of this simple and elegant technique.
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paper_title: Fast three-dimensional form measurement system

paper_content:

The optical 3-D measuring system described measures the shape of objects at high speed and in a true noncontact fashion. The system evaluates and displays the object points visible within the field of view of the CCD camera integrated within the system. A description of the system and some applications is given, and the potential for further evaluation or processing of the measured data is highlighted.
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paper_title: Improved Stripe Matching for Colour Encoded Structured Light

paper_content:

The identification of stripes in colour-encoded structured light images has previously been implemented only on a raster scan basis, recursively picking a raster and identifying intersecting stripes until all are identified. This technique is inadequate since sub-sequences of stripes may not all intersect a given stripe, and the first line chosen may give incorrect matching information on which subsequent matches will be based. In this paper we present a new technique which uses a directed acyclic graph to represent stripe ordering, then cost-matches the graph consistently. The theory and advantages of the technique are explained, and details of implementation are given.
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paper_title: Handy rangefinder for active robot vision

paper_content:

A compact and high-speed rangefinding system which is applicable to active robot vision is described. The principle of depth measurement is based on the space encoding method. Spatial coded patterns of light are generated by a semiconductor laser. A slit-ray of the laser is scanned by a rotating polygonal mirror and switched according to temporal switching patterns. Each pattern of light is generated, and its reflected image is taken by a CCD camera, in one image frame with no lag time. A 512/spl times/256 range map is obtained continuously every 0.2 seconds.
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paper_title: Color-Encoded Structured Light for Rapid Active Ranging

paper_content:

In this paper, we discuss a novel strategy for rapid acquisition of the range map of a scene employing color-encoded structured light. This technique offers several potential advantages including increased speed and improved accuracy. In this approach we illuminate the scene with a single encoded grid of colored light stripes. The indexing problem, that of matching a detected image plane stripe with its position in the projection grid, is solved from a knowledge of the color grid encoding. In fact, the possibility exists for the first time to acquire high-resolution range data in real time for modest cost, since only a single projection and single color image are required. Grid to grid alignment problems associated with previous multistripe techniques are eliminated, as is the requirement for dark interstices between grid stripes. Scene illumination is more uniform, simplifying the stripe detection problem, and mechanical difficulties associated with the equipment design are significantly reduced.
---
paper_title: Range Sensing By Projecting Multiple Slits With Random Cuts

paper_content:

In this paper, we describe a range sensing method by projecting a single pattern of multiple slits. To obtain 3D data by projecting a single pattern, certain codes for identifying each slit must be contained in the patten. In our method, random dots are used to identify each slit. The random dots are given as randomly distributed cuts on each slit. Thus, each slit is divided into many small line segments and using these segments as features, stereo matching is carried out to obtain 3D data. Using adjacent relations among slit-segments, the false matches are reduced and segment pairs, whose adjacent segments also correspond with each other, are extracted and considered to be correct matches. Then, from the resultant matches, the correspondence is propagated by utilizing the adjacency relationships to get an entire range image.
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paper_title: Range imaging based on moving pattern light and spatio-temporal matched filter

paper_content:

Aa new structured light projection method for measuring 3D and range objects is proposed. The method projects a moving structured light pattern modulated by a time-compression signal, then the objects are captured as a dynamic and spatio-temporal image by a camera. By applying a matched filter to the spatio-temporal image, the ideal slit light is realized even using an actual light projector. According to the extracted slit light and triangulation principle, 3D geometric information of the objects scene are obtained more accurately. By using separable signals which have no correlation with each other, the method is able to project multiple light patterns at different positions simultaneously. It solves the occlusion problem due to a single projector. Some experimental results show its advantages.
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paper_title: Automatic fringe pattern analysis: a review

paper_content:

Abstract The wide availability of digital image processing equipment has led to the development of a large number of techniques for analysing interference fringe patterns. Concentrating on the most recent developments in the field, this paper presents a cross-section of techniques and applications of automatic and interactive fringe pattern analysis. The paper also describes some of the ways in which prior knowledge of the fringe pattern characteristics can be used to simplify the analysis procedure.
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paper_title: 3-D data acquisition by Rainbow Range Finder

paper_content:

The Rainbow Range Finder (RRF) has the ability to obtain range information for all image pixels with only one frame TV camera imaging during 1/30 s. The authors propose a novel practical calibration scheme which makes range measurement for all visible pixels possible. An experimental system was developed on that basis, and measurement accuracy was evaluated. A curved surface and a plain surface could be measured with sufficient accuracy. The feasibility of a real-time system with an accuracy of 1% in regard to the measurement region size was demonstrated. >
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paper_title: Range image acquisition with a single binary-encoded light pattern

paper_content:

The problem of strike identification in range image acquisition systems based on triangulation with periodically structured illumination is discussed. A coding scheme is presented based on a single fixed binary encoded illumination pattern, which contains all the information required to identify the individual strikes visible in the camera image. Every sample point indicated by the light pattern is made identifiable by means of a binary signature, which is locally shared among its closest neighbors. The applied code is derived from pseudonoise sequences, and it is optimized so that it can make the identification fault-tolerant to the largest extent. A prototype measurement system based on this coding principle is presented. Experimental results obtained with the measurement system are also presented. >
---
paper_title: 3D reconstruction using an uncalibrated stereo pair of encoded images

paper_content:

The reconstruction of three dimensional (3-D) objects is used in CAD/CAM, robotics, remote sensing, etc. The models (images) can be either directly acquired by using special devices such as range finders, CTR scanners, etc. or they can be recovered from a series of 2-D images of the object. The authors report on a new method for reconstructing 3-D objects from two 2-D images using CCD cameras. This method uses a pseudo-random encoded grid projected on the object. The grid nodes are used in matching left to right 2-D images. The set of matched points are further used to calculate the disparity of each point of the object surface. Experimental examples illustrate the performance of this simple and elegant technique.
---
paper_title: Improved Stripe Matching for Colour Encoded Structured Light

paper_content:

The identification of stripes in colour-encoded structured light images has previously been implemented only on a raster scan basis, recursively picking a raster and identifying intersecting stripes until all are identified. This technique is inadequate since sub-sequences of stripes may not all intersect a given stripe, and the first line chosen may give incorrect matching information on which subsequent matches will be based. In this paper we present a new technique which uses a directed acyclic graph to represent stripe ordering, then cost-matches the graph consistently. The theory and advantages of the technique are explained, and details of implementation are given.
---
paper_title: Color-Encoded Structured Light for Rapid Active Ranging

paper_content:

In this paper, we discuss a novel strategy for rapid acquisition of the range map of a scene employing color-encoded structured light. This technique offers several potential advantages including increased speed and improved accuracy. In this approach we illuminate the scene with a single encoded grid of colored light stripes. The indexing problem, that of matching a detected image plane stripe with its position in the projection grid, is solved from a knowledge of the color grid encoding. In fact, the possibility exists for the first time to acquire high-resolution range data in real time for modest cost, since only a single projection and single color image are required. Grid to grid alignment problems associated with previous multistripe techniques are eliminated, as is the requirement for dark interstices between grid stripes. Scene illumination is more uniform, simplifying the stripe detection problem, and mechanical difficulties associated with the equipment design are significantly reduced.
---
paper_title: Range Sensing By Projecting Multiple Slits With Random Cuts

paper_content:

In this paper, we describe a range sensing method by projecting a single pattern of multiple slits. To obtain 3D data by projecting a single pattern, certain codes for identifying each slit must be contained in the patten. In our method, random dots are used to identify each slit. The random dots are given as randomly distributed cuts on each slit. Thus, each slit is divided into many small line segments and using these segments as features, stereo matching is carried out to obtain 3D data. Using adjacent relations among slit-segments, the false matches are reduced and segment pairs, whose adjacent segments also correspond with each other, are extracted and considered to be correct matches. Then, from the resultant matches, the correspondence is propagated by utilizing the adjacency relationships to get an entire range image.
---
paper_title: Structured light patterns for robot mobility

paper_content:

The authors describe some of the important operational considerations and image processing tasks required to utilize a nonscanning structured-light range sensor in path planning for robot mobility. The efforts have concentrated on the geometric design of the projectional grid with regard to smoothing of fine-scale range texture, and the development of image processing techniques in order to extract the deformed grid from the image. Particular emphasis is placed on the issues of operating in ambient lighting, smoothing of range texture, grid pattern selection, albedo normalization, grid extraction, and coarse registration of images to the projected grid. Once the grid is extracted, its global order allows intersections to be labeled, and disparities assigned and converted to range data. This range map can then be converted to a 'topography map' to be used for planning short-range paths through the environment while avoiding obstacles. >
---
paper_title: 3-D data acquisition by Rainbow Range Finder

paper_content:

The Rainbow Range Finder (RRF) has the ability to obtain range information for all image pixels with only one frame TV camera imaging during 1/30 s. The authors propose a novel practical calibration scheme which makes range measurement for all visible pixels possible. An experimental system was developed on that basis, and measurement accuracy was evaluated. A curved surface and a plain surface could be measured with sufficient accuracy. The feasibility of a real-time system with an accuracy of 1% in regard to the measurement region size was demonstrated. >
---
paper_title: Shape detection of small specular surface using color stripe lighting

paper_content:

A method to detect the shape of specular surfaces is required to inspect precise metal parts or solder joints visually. A method to detect the 3D shape of specular surfaces is introduced. The system uses color stripe lighting. Reflected colors from specular surfaces are determined to detect normal directions of the surface. From the normal directions of the surface the height changes are calculated, and from the height changes the 3D shape. >
---
paper_title: Range image acquisition with a single binary-encoded light pattern

paper_content:

The problem of strike identification in range image acquisition systems based on triangulation with periodically structured illumination is discussed. A coding scheme is presented based on a single fixed binary encoded illumination pattern, which contains all the information required to identify the individual strikes visible in the camera image. Every sample point indicated by the light pattern is made identifiable by means of a binary signature, which is locally shared among its closest neighbors. The applied code is derived from pseudonoise sequences, and it is optimized so that it can make the identification fault-tolerant to the largest extent. A prototype measurement system based on this coding principle is presented. Experimental results obtained with the measurement system are also presented. >
---

Title: An Overview of the Advantages and Constraints of Coded Pattern Projection Techniques for Autonomous Navigation

Section 1: Introduction
Description 1: Introduce the topic of obtaining 3D information from unknown scenes, comparing passive and active methods, and explaining the structured coded light technique.

Section 2: Coded structured light
Description 2: Discuss the use of coded structured light to alleviate the correspondence problem in obtaining 3D information and explain various techniques and configurations.

Section 3: Overview : coded structured light techniques
Description 3: Provide an in-depth overview and analysis of several coded structured light methods proposed in recent years, detailing their advantages and constraints.

Section 4: Conclusions
Description 4: Summarize the main findings and discuss the essential problems associated with coded pattern projection techniques, including their use in dynamic and static scenes, and their application in different types of surfaces.