Digital Photogrammetric System Research Articles

Evaluation of Information Loss in Digital Elevation Models With Digital Photogrammetric Systems

Information loss is caused when a surface is sampled with a finite interval, such as in the production of a digital elevation model (DEM). This information loss can become the dominant part of the error in a DEM. The ability to quantify information loss enables guidance to be provided for an appropriate choice of grid interval and better accuracy assessment for the DEM. With the use of digital photogrammetric systems, evaluation of information loss has become much easier. This paper describes three methods of evaluating information loss. An example is given of the method which is most appropriate for use with a digital photogrammetric system, based on rock cliff surface data and the VirtuoZo system.

Digital Photogrammetry and Microscope Photographs

The feasibility of applying commercial digital photogrammetric software to the measurement of small objects photographed through an optical microscope has been examined. The objects, about 20 mm across, were photographed using a 35 mm film camera (at the lowest magnification setting of the Olympus microscope) giving photographs at a scale of 2:1. The photographs were then scanned before processing with the VirtuoZo digital photogrammetric system. Various problems needed to be overcome, some due to the limited options available with the highly automated digital system which was not designed for such measurement tasks. The unusual image scales, the uncommon pixel sizes and the unconventional and uncertain imaging geometry, all impeded immediate photogrammetric implementation. Photographic problems with the microscope were also faced, as with all microscope photogrammetry. Creating control points and independently assessing the accuracy of results at these scales were also difficult operations, but an analytical plotter was utilized for both these purposes and to verify the imaging geometry. Once such problems were overcome, image matching proceeded well and an accurate DTM could be created successfully, provided that a suitably textured object was chosen.

Accuracy Assessment of Digital Elevation Models Generated Using the Erdas Imagine Orthomax Digital Photogrammetric System

The users of many digital photogrammetric systems are allowed a degree of control over the automated digital elevation model (DEM) generation software with a set of strategy parameters. These parameters control the search and quality control characteristics of the algorithm; hence the wrong choice of parameters can have a significant detrimental effect on the accuracy of the DEM. This paper describes the strategy parameters used in the Erdas Imagine OrthoMAX digital photogrammetric system and a set of tests used to define the optimum set of parameters for a project. The algorithm employs an area correlator and a hierarchical approach in the matching process. The results show that a 35 per cent increase in accuracy can be achieved through the process of parameter optimization. They also demonstrate that changes to the strategy parameters have a similar effect on the results for all areas of a set of imagery used in the test, which is of particular note because the imagery contains a diverse range of landcover types. The paper additionally provides a description of a system currently being developed which will automatically prescribe the correct set of parameters for a project.

Photogrammetric Solutions for Industrial Automation and Process Control

Digital photogrammetric systems have been introduced to solve various measurement problems in industrial applications for many years, ever since high resolution CCD cameras and powerful computer technologies have been available. For a successful implementation of a digital photogrammetric system into the production line, not only does the actual measurement task have to be solved but also a complete integration of the system into the production process usually has to be supplied by the system manufacturer. Three examples of successful implementations of photogrammetric systems for industrial automation and process control are presented in this paper.

Digital underwater photogrammetric system for large scale underwater spatial information acquisition

An UNderwater Digital Photogrammetric System (UNDIPS) has been developed jointly by The University of Calgary and Canadian Hydrographic Services (CHS). An underwater photogrammetric model considering the lens distortion, housing cover corrections, and the medium refraction has been developed. It corrects the displacements of image points caused by the distortion and refraction so that the photogrammetric processing can be treated as a reduced central perspective transformation and modified direct linear transformation (DLT) can be applied. The calibration of the system is performed in two phases. This allows the examination of characteristics of the system associated with the cameras, the housing covers, and the medium refractions separately. With the current configuration, the achievable accuracy of object points which are 2–2.5 m from the cameras in the object space is 0.3 cm in the x and y directions and 1.0 cm in the z direction (depth).

CCD Image System Design And Exploitation: Experiences And Lessons Learned

The use of digital imagery, acquired through charge‐coupled devices (CCDs) either by the scanning of hard copy film or direct capture through the use of a CCD camera, has fundamentally changed the photogrammetric environment. In order to fully exploit these digital image data, the photogrammetrist must employ system design, implementation philosophies and processing methodologies different from those of traditional film based photogrammetry. It is now possible for these new photogrammetric systems to be operated from low cost, high performance PC and Macintosh class commercial hardware, using vendor supplied software for user developed applications.This paper explores lessons learned and experiences gained from low cost, digital photogrammetric system development and CCD image exploitation. Examples and discussion presented in this paper include: (1) integration of user developed applications with commercial hardware and software; (2) user interface design; (3) validation of processing algorithms within the digital image domain; (4) system calibration; (5) digital image data handling, management and storage; and (6) image data compression. The film based photogrammetric system provides the point of departure to digital photogrammetry. Technical knowledge, system design and implementation and CCD image exploitation provide the experience.

Automatically-controlled analyser for intererograms

A simple low-cost digital photogrammetric system for interpreting Mach-Zehnder interferograms is described. The associated software permits the rates of heat transfer occurring within test cells of two-dimensional section to be deduced. The interferograms may be analysed quantitatively much more rapidly, and with less supervision, via this facility, than by the laborious conventional technique of using a travelling microscope.

An Integrated Digital Mapping System

There is an increasing demand for terrain information in digital form in addition to graphical format. Under such circumstances the establishment of a national digital topographic data base can be envisaged and implemented to serve the needs for terrain data in either digital and/or graphical format. This paper discusses the digital interactive photogrammetric data acquisition system, interactive cartographic editing and automated drafting. The concepts of digital topographic data bank and data base are discussed as well as the requirements for selective retrieval and data base query language capability.