CLOSE RANGE DIGITAL PHOTOGRAMMETRY TECHNIQUES APPLIED TO LANDSLIDES MONITORING
This paper deals about the use of non metric reflex digital cameras in landslide monitoring and the analysis of landscape evolution from comparison of present digital photographs and old digitized analogue metric terrestrial photographs. The methodology has been improved in a test area (a slope along a road with instability processes in southern Spain) where terrain failures have been documented in the last ten years. Several photogrammetric techniques were checked as well as combination of both convergent (for calibration and densification) and stereoscopic (for DTM generation) networks. Considerations about the use of terrestrial LIDAR and a comparative example are also made. This paper is included in a wider research project carried out in Northern and Southern Spain for study landslides. This research project (MAPMUT: The improvement of susceptibility analysis by means of useful digital models of the terrain geometry), aims with an improvement of susceptibility maps using high quality input information.
EVALUATION OF A DIGITAL NON METRIC CAMERA ( CANON D 30 ) FOR THE PHOTOGRAMMETRIC RECORDING OF HISTORICAL BUILDINGS
This paper is about the evaluation of a digital non-metric reflex camera (Canon D30) for low cost applications in archaeology, architecture and cultural heritage. At present digital cameras of different geometric qualities are being routinely used for this purposes. The Canon D30 digital camera is a professional camera with a CMOS sensor of 3.2 Mp. Although camera resolution is relatively low, compared with more recent amateur cameras, the sensor is slightly smaller in size than conventional 35 mm film format. The focal length/angle of view conversion factor is approximately 1.6x compared to full frame 35 mm film format. This property makes very interesting the use of this camera in cultural heritage photogrammetric applications, where both accuracy and final image quality are quite important. The camera internal geometry has been solved by means of self calibration with own developed software. First self calibration was made at laboratory using digital target measurement at subpixel accuracy. Proportional accuracies with this method were between 1:20.000 and 1:30.000. But additional self calibrations where carried out with field control points. In this case, accuracy reached was poorest because images were manually measured on natural points, but it was for normal architectural/archaeological applications enough. As main drawback of this camera we can point out the low sensor resolution. So when camera/object distance increases or high oblique photographs are employed the image quality of the final product reduces considerably.
The effect of collimation on image quality and radiation safety in digital radiography of small animals
Collimating the primary x-ray beam to the specific area of anatomic interest has traditionally been strongly recommended to produce high quality radiographic images, even though some small animal patients can fit their entire torso on a single radiographic casette or detector. However, modern digital radiography may allow for whole-body projections for these patients at similar quality to specific collimated projections. Lateral and ventrodorsal projections of 31 small dogs were obtained to evaluate the effect of collimation on the quality of the resulting digital radiograph. Each projection was performed using both a collimated and whole-body technique. Scatter radiation was detected during each exposure as well to determine the effect of collimation on radiation safety for veterinary personnel. The resulting images were cropped to portray only the thorax, and were evaluated by five radiologists blinded to the procedure used for each image. Visual grading characteristics analysis was performed. An overall trend towards higher image quality was found in the collimated approach compared to the whole-body, but in most cases this change was not significant. Overall image quality for the ventrodorsal images was found to be significantly better in the collimated approach compared to the whole-body. Evaluation of image histograms suggests that the application of digital processing and the look-up table differs between them, and this may account for a large portion of any quality difference. Over twice as much scatter radiation was detected during the whole-body images as during the collimated images. Overall image quality was rated as adequate to high for almost all images with both approaches. Adequate collimation remains recommended to provide the highest quality images with the lowest exposure to veterinary personnel.