Hirofumi Chikatsu

Camera-Variant Calibration and Sensor Modeling for Practical Photogrammetry in Archeological Sites

With the appearance of low-cost and high-resolution consumer-grade digital cameras, a practical three-dimensional (3D) measurement system using a consumer-grade digital camera is greatly anticipated in various fields. In these circumstances, the authors have been concentrating on developing a practical 3D measurement system that includes photogrammetric software called the Image Based Integrated Measurement (IBIM) system. The IBIM system device consists of full/half-mirrors, a consumer-grade digital camera, and a laser distance meter. The most remarkable advantage of the system is its ability to calculate exterior orientation parameters, interior orientation parameters, and pseudo ground control points (GCPs) without using scale bars or the GCPs in the object field. The system has the ability to calibrate multiple cameras of different resolutions using a camera-variant parameter set. However, there remains one issue that needs to be resolved before this system can be effectively used, namely, improvement of the system which does not depend on the IBIM system device. With this motive, a practical photogrammetry method using a consumer-grade digital cameras and a hand-held laser distance meter is proposed. To test our proposed method, the bundle of distances from the center camera position to the feature points in the object field were measured individually at archaeological sites in Greece. In order to evaluate the possibility and practicability of the proposed photogrammetry method, this paper describes and evaluates the camera calibration techniques using images from multiple cameras of different resolutions and a bundle of distances.

Comparative evaluation of consumer grade cameras and mobile phone cameras for close range photogrammetry

The authors have been concentrating on developing convenient 3D measurement methods using consumer grade digital cameras, and it was concluded that consumer grade digital cameras are expected to become a useful photogrammetric device for the various close range application fields. On the other hand, mobile phone cameras which have 10 mega pixels were appeared on the market in Japan. In these circumstances, we are faced with alternative epoch-making problem whether mobile phone cameras are able to take the place of consumer grade digital cameras in close range photogrammetric applications. In order to evaluate potentials of mobile phone cameras in close range photogrammetry, comparative evaluation between mobile phone cameras and consumer grade digital cameras are investigated in this paper with respect to lens distortion, reliability, stability and robustness. The calibration tests for 16 mobile phone cameras and 50 consumer grade digital cameras were conducted indoors using test target. Furthermore, practability of mobile phone camera for close range photogrammetry was evaluated outdoors. This paper presents that mobile phone cameras have ability to take the place of consumer grade digital cameras, and develop the market in digital photogrammetric fields.

Building extraction and modeling in urban area by image sequence analysis

3D city modeling from airborne imagery includes mainly two parts: (1) image processing procedures and (2) 3D modeling for man-made objects such as buildings, roads and other objects. Line or feature extraction and stereo matching are usually utilized as an image processing procedures, and geometrical data acquisition for man-made objects are performed. However, there are some issues for automatic or semi-automatic man-made object modeling. These problems include uncertainty within matching, extraction of man-made objects and spatial data acquisition. In particular, spatial data acquisition of buildings are important for reliable city modeling. With this objective, this paper focuses especially on efficient and robust line matching method using optical flow, which enable an automatic building extraction since line gives important information for building extraction and satisfied results are depend on rigorous line extraction and matching. Furthermore, building extraction using morphological opening and 3D modeling for urban area are also investigated in this paper.

Shadow correction in high dynamic range images for generating orthophotos

High dynamic range imagery is widely used in remote sensing. With the widespread use of aerial digital cameras such as the DMC, ADS40, RMK-D, and UltraCamD, high dynamic range imaging is generally expected for generating minuteness orthophotos in digital aerial photogrammetry. However, high dynamic range images (12-bit, 4,096 gray levels) are generally compressed into an 8-bit depth digital image (256 gray levels) owing to huge amount of data and interface with peripherals such as monitors and printers. This means that a great deal of image data is eliminated from the original image, and this introduces a new shadow problem. In particular, the influence of shadows in urban areas causes serious problems when generating minuteness orthophotos and performing house detection. Therefore, shadow problems can be solved by addressing the image compression problems. There is a large body of literature on image compression techniques such as logarithmic compression and tone mapping algorithms. However, logarithmic compression tends to cause loss of details in dark and/or light areas. Furthermore, the logarithmic method intends to operate on the full scene. This means that high-resolution luminance information can not be obtained. Even though tone mapping algorithms have the ability to operate over both full scene and local scene, background knowledge is required. To resolve the shadow problem in digital aerial photogrammetry, shadow areas should be recognized and corrected automatically without the loss of luminance information. To this end, a practical shadow correction method using 12-bit real data acquired by DMC is investigated in this paper.

Practical calibration for consumer grade digital camera with integrated high zooming lens

Although zoom lens has been widely accepted in vision system, the use of zoom lens was not general in close range photogrammetry from the view point of instability by zooming. However, with the spread of consumer grade digital cameras with integrated zoom lens, in particular long range such as ×35, digital close range photogrammetry using the camera is enormously expected in various application fields. There is a large body of literature on calibration of zoom lens. However, there is still problem for effective digital photogrammetry using the camera. The problem is practical calibration model for zoom lens, in particular correction of misalignment which is caused by zoom setting. In order to resolve instability of zoom lens, and practical use of digital close range photogrammetry using zoom lens, a new calibration model is proposed in this paper based on correction of zoom lens misalignment. Furthermore, in order to evaluate the proposed calibration model for zoom lens, calibration tests were conducted using 5 kinds of consumer grade digital camera with integrated zoom lens (×3~5), 3 kinds of long range consumer grade digital camera (×12~30) and digital SLR camera with zoom lens (×11).

Performance evaluation of macro lens in digital close range photogrammetry

Recently, the documentation and visualization of various cultural heritages have been receiving attention, and a small Buddha such as less than 10 cm tall which was stored in the womb of Buddha is also included in cultural heritages. Zoom lenses are generally used to document these small objects and thus conserve the cultural heritage. However, there exist certain issues pertaining to the use of zoom lenses for such digital documentation. These issues include image sharpness and distortions that occur with changes in focal length setting, and in particular, the depth of field is issue from application standpoint such as documentation of the small cultural heritage. On the other hand, macro lenses can be used to capture sharp images of small objects from the view point of working distance, and its depth of field is related to the aperture of the camera. In order to evaluate the effectiveness of macro lenses in digital close range photogrammetry, macro lens and zoom lens were mounted on a digital single lens reflex camera (Canon EOS20D, 8.2 Mega pixels). This paper deals in a first part with comparative evaluations for both lenses with respect to their lens distortion, imaging mode, and calibration aspects. The results indicated that macro lenses were more suitable for digital close range photogrammetry. Calibration tests are performed to demonstrate the effectiveness and practicability of macro lens in close range photogrammetic applications.

Efficient corner detector for 3D point crowd data and application to 3D modeling of structures

Recently, a laser scanner has been receiving more attention as a useful tool for real-time 3D data acquisition, and various applications such as city modeling, DTM generation and 3D modeling of cultural heritage were proposed. However, robust filtering for distinguish on- and off-terrain points from point cloud 3D data collected by airborne laser scanner is still issues. In particular, filtering of point cloud 3D data collected by terrestrial laser scanner has more severe problems caused by many occlusion parts, windows, few the deepest points, wall of buildings and so on. In order to perform 3D texture modeling of cultural heritage using terrestrial laser ranging data, texture modeling method are investigated in this paper, and proposed filtering method is based on flatness within 30*30cm. Flatness area (ground surface, wall of structures, etc.) and non-flatness area (trees, bushes, etc.) is classified using measurement result of many target., and non-flatness areas are interpolated using morphological procedure. The filtering method shows very robust result, and the most remarkable point of this filtering method is its ability to obtain break-lines which give important information for 3D modeling since 3D model of historical structure are consists of flatness areas (e.g. roof, wall, pillar). Therefore, surface patch of 3D model is identified by extracting a flatness area which is surrounded by break-line, and 3D model for the patch is generated using point cloud 3D data along the frame of the patch. Furthermore, curve points for surface patch are detected from break-line, and a surface patch is generated in automatically step-by-step, texture modeling will be done with the surface patch and digital image. Therefore, automatic detection of the curve point, which is necessary for model making, is very difficult. Because, break-line includes a lot of small curve points. In this paper, we particularly watched this problem and carried out promotion of efficiency of model making by developing a solution method. With these processes, efficient 3D representation using textured model is performed without any processes. This paper presents 3D textured modeling method for historical structure using terrestrial laser ranging data and break-line by flatness evaluation, detection method of curve point using break-line.

Efficient estimation of orthophoto images using visibility restriction

The orthophoto image which is generated using an aerial photo is used in river management, road design and the various fields since the orthophoto has ability to visualize land use with position information. However, the image distortion often occurs in the ortho rectification process. This image distortion is used to estimate manually by the evaluation person with great time. The image distortion should be automatically estimated from the view point of efficiency of the process. With this motive, formed angle V between view vector at exposure point and normal vector at center point of a patch area was focused in this paper. In order to evaluate the relation between image distortion and formed angle V, DMC image which were acquired 2000m height were used and formed angle V for 10m×10m patch was adopted for computing visibility restriction. It was confirmed that image distortion occurred for the patch which show rather than 69 degree of the formed angle V. Therefore, it is concluded that efficient orthophoto visibility restriction is able to perform using the formed angle V as visibility restriction in this paper.

Practical target location and accuracy indicator in digital close range photogrammetry using consumer grade cameras

Recently, pixel numbers and functions of consumer grade digital camera are amazingly increasing by modern semiconductor and digital technology, and there are many low-priced consumer grade digital cameras which have more than 10 mega pixels on the market in Japan. In these circumstances, digital photogrammetry using consumer grade cameras is enormously expected in various application fields. There is a large body of literature on calibration of consumer grade digital cameras and circular target location. Target location with subpixel accuracy had been investigated as a star tracker issue, and many target location algorithms have been carried out. It is widely accepted that the least squares models with ellipse fitting is the most accurate algorithm. However, there are still problems for efficient digital close range photogrammetry. These problems are reconfirmation of the target location algorithms with subpixel accuracy for consumer grade digital cameras, relationship between number of edge points along target boundary and accuracy, and an indicator for estimating the accuracy of normal digital close range photogrammetry using consumer grade cameras. With this motive, an empirical testing of several algorithms for target location with subpixel accuracy and an indicator for estimating the accuracy are investigated in this paper using real data which were acquired indoors using 7 consumer grade digital cameras which have 7.2 mega pixels to 14.7 mega pixels.

DTM generation in forested area using multiple return pulses from airborne laser scanner

Airborne laser scanner is widely adopted for city modeling, DTM (Digital Terrain Model) generation, monitoring electrical power lines and detection of forest areas. In generally, airborne laser scanning enables to acquire point cloud 3D data for surface of the ground or objects using multiple return pulses (first, last and other pulse). Filtering for distinguish on- and off-terrain points from point cloud 3D data which are collected by airborne laser scanner was issue, and various filtering methods have been developing for generating DTM using point cloud 3D data. Waveform information (range, pulse amplitude, pulse width) which is corrected by resent laser scanner system has been receiving more attention for improvement of classifying the point cloud data into on- and off-terrain points. Waveform information has ability to classify the point cloud data, however, robust filtering for distinguish on- and off-terrain points is still issue. The main problem is robust extraction of the deepest points which shows ground surface. As many filtering and classifying methods for robust extraction of the deepest points were proposed including waveform information, the problem reaches extraction of the last pulse since the last pulse show the deepest points. With this motive, filtering and classifying approach for DTM generation in forested area using multiple return pulses instead of waveform information are investigated in this paper.