Abstract
In 2014 the Institut Cartogràfic i Geològic de Catalunya (ICGC) decided to incorporate digital oblique imagery in its portfolio in response to the growing demand for this product. The reason can be attributed to its useful applications in a wide variety of fields and, most recently, to an increasing interest in 3d modeling. The selection phase for a digital oblique camera led to the purchase of the Leica RCD30 Oblique system, an 80MPixel multispectral medium-format camera which consists of one Nadir camera and four oblique viewing cameras acquiring images at an off-Nadir angle of 35º. The system also has a multi-directional motion compensation on-board system to deliver the highest image quality. <br><br> The emergence of airborne oblique cameras has run in parallel to the inclusion of computer vision algorithms into the traditional photogrammetric workflows. Such algorithms rely on having multiple views of the same area of interest and take advantage of the image redundancy for automatic feature extraction. The multiview capability is highly fostered by the use of oblique systems which capture simultaneously different points of view for each camera shot. Different companies and NMAs have started pilot projects to assess the capabilities of the 3D mesh that can be obtained using correlation techniques. Beyond a software prototyping phase, and taking into account the currently immature state of several components of the oblique imagery workflow, the ICGC has focused on deploying a real production environment with special interest on matching the performance and quality of the existing production lines based on classical Nadir images. <br><br> This paper introduces different test scenarios and layouts to analyze the impact of different variables on the geometric and radiometric performance. Different variables such as flight altitude, side and forward overlap and ground control point measurements and location have been considered for the evaluation of aerial triangulation and stereo plotting. Furthermore, two different flight configurations have been designed to measure the quality of the absolute radiometric calibration and the resolving power of the system. <br><br> To quantify the effective resolution power of RCD30 Oblique images, a tool based on the computation of the Line Spread Function has been developed. The tool processes a region of interest that contains a single contour in order to extract a numerical measure of edge smoothness for a same flight session. The ICGC is highly devoted to derive information from satellite and airborne multispectral remote sensing imagery. A seamless Normalized Difference Vegetation Index (NDVI) retrieved from Digital Metric Camera (DMC) reflectance imagery is one of the products of ICGC’s portfolio. As an evolution of this well-defined product, this paper presents an evaluation of the absolute radiometric calibration of the RCD30 Oblique sensor. To assess the quality of the measure, the ICGC has developed a procedure based on simultaneous acquisition of RCD30 Oblique imagery and radiometric calibrated AISA (Airborne Hyperspectral Imaging System) imagery.
Highlights
The Institut Cartogràfic i Geològic de Catalunya (ICGC) is the mapping agency of the Government of Catalonia
Maintaining up-to-date information at smaller scales, the ICGC is very concerned about the specific geoinformation required for managing the ever growing urban areas (UN World Urbanization Trend forecasts that 86% of the population of the developed world will live in urban areas by 2050)
From the whole set of models present in the market, the ICGC decided to acquire in 2014, the RCD30 oblique featured by Leica: a 60Mpixel multispectral medium format camera which consists of one Nadir and four oblique cameras viewing towards the four cardinal points at an off-Nadir angle of 35o
Summary
The Institut Cartogràfic i Geològic de Catalunya (ICGC) is the mapping agency of the Government of Catalonia. Some of the environmental or energy efficiency applications developed at ICGC for urban planning (such as light pollution, thermal efficiency, Urban Heat Island analysis) are related to specific hyperspectral surveys, but there is an increasing requirement of including detailed and photorealistic 3D models for specific morphological analysis and as a base layer of the urban information infrastructure, moving from 2D to 3D environments. The ICGC acquired the oblique camera system in 2014 with the objective of adding a new urban sensor to its portfolio, which enables the creation of photorealistic 3D meshes using multi-view pixel-based algorithms, and the evolution of the current product portfolio In such evolution, ICGC’s analysis aims at increasing the productivity of the oblique flight surveys by maximizing the number of applications derived from the captured information, including 3D meshes, point cloud and façade textures, NDVI orthoimagery and stereo-models for data capture at 1:1000 scale. The study of geometric and radiometric suitability of the RDC30 camera for remote sensing applications and stereo plotting at urban scales; on the other hand, the study of the automated aerial triangulation of Nadir and oblique blocks which is challenged by the number of images involved in the high-overlap flight surveys, the scale and resolution variations along the oblique images and the performance of dense point matching across the different viewing directions
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