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(Submission #346)
INSPIRE Orthoimagery theme includes two main different types of data:
- Aerial orthophotos: the main needs being efficient data production and storage, fast and flexible multiscale visualization and overlay with light web clients or desktop GIS programs through Internet (WMS, WMTS or WCS services) together with the maximum preservation of original image quality.
- Satellite orthoimages for remote sensing: the main needs are quick processing of massive amounts of data for multitemporal and multiscale analysis, integration of data from multiple satellites, quasi-real time processing and information dissemination, together with the maximum preservation of original radiometric values.
Digital Elevation Models and orthoimages are mutually complementary. For this reason, it is very important to maximize the interoperability between both kinds of datasets.
But usual workflows for production, archiving, dissemination and use of orthoimages pose important interoperability problems: empty wedges, images in different zones of the map projections, non-alignment of pixels at the different levels of the pyramids and the need to apply multiple resamplings and compression-decompression cycles, among others
These problems make it impossible to overlay, compare and mosaic different orthoimages without resampling them, which causes degradation of image quality and great costs in processing time. These problems imply great inefficiencies in production, dissemination through web services and processing in “Big Data” environments. Elevation data suffer from these same problems described for orthoimagery.
Most of the requirements mentioned above can be addressed with the use of a common “nested grid” for mutirresolution production, archiving, dissemination and use of orthoimagery, digital elevation models and other raster data. Such a nested grid must be complemented by an appropriate “tiling schema” based on the “quad-tree” concept.
In this paper we propose the use of Web Mercator tiling schema as common nested grid for orthoimagery and Digital Elevation Models. The use of this nested grid sets the basis for the solution to most of the interoperability problems mentioned above. But Web Mercator tiling schema has an important problem: pixel sizes (meters/pixel) in this schema are not integer, as we are used to. Instead, they are irrational real numbers (thus with an infinite number of decimals). We propose a solution to this problem, through the use of a secant Mercator projection.
In order to adopt the proposed nested grid and TIFF options, some minor but important changes must be made to Inspire Data Specifications on Orthoimagery, Elevations, Coordinate Reference Systems and Geographical Grid Systems.
Topic Area: [2.9] Challenges and approaches to standardization of data and interoperability of systems. Abstract Type: Oral Presentation
Comments: nested grids, orthoimages, digital elevation models, coordinate reference systems
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