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TModeling.DTMsFromMultipleDatasets
r1.1 - 03 May 2005 - 19:23 - Main.guest
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---+ DTMs from multiple datasets ---++ Production of an integrated digital terrain model from multiple datasets of different quality [1] ---++ Overview * Describes production of a DTM from multiple input sets * Claim that result is better than any of the parts * Assumes that multiple DTMs are available for study area * Implementation not ready for commercial use ---+++ DEMs * Digital Elevation Models * Rasterized, contain elevation data for each cell * Elevation can be discrete (assumed to be uniform throughout cell, changes on cell boundary) or continuous ---+++ DTMs * Digital Terrain Models * Assumed to be continuous * Contains elevation data and other features that define surface [1] * Slope * Curvature * Gradient ---++ Techniques used ---+++ Simultaneous interpolation * As name implies, interpolate all sources at once * Least squares interpolation * Predict new location from surrounding values * Weight different data sources depending on quality * Use characteristic features from different sources * Each feature can come from only one source * Often poorly distributed * Use "automatic eliminiation and densification" [1] * Remove points that are too far from the surface being predicted * Need to find good weight distribution * Based on strength of correlation among points ---+++ Geomorphologic enhancement * Not well-defined; assume audience will know particulars * DTM statistically usually too smooth -- use these enhancements to closer approximate reality * Use averages, take quality into consideration * Find proper weights to reflect quality * Apply best geomorphological characteristics * Go from lowest quality to highest quality for best results * Error goes down as more sources considered * Apply geomorphological enhancements at end * Don't really explain why * Unique grid size for all sources imposed on final result ---++ Steps involved ---+++ Pre-processing * Visual evaluation, eliminate gross errors * Cut hole in layer and look at other layers * Statistical elimination of bad points * need high-quality DTM to do this * Use updated reference points * Tell how accurate data is * Can give inaccurate picture -- most reference points are in areas with high accuracy already ---+++ Processing * Mosaicing * Reference points * Also used to improve final result * Elevation only; no geomorphological information * Only considered if within threshold * Temporal differences * Correct absolutely: remove outdated info and replace with something else * Used for man-made changes (roads, quarries) * Correct relatively: apply difference surface to bring up to date * Used for natural changes (volcanoes, landslides) ---++ Evaluation * Give applications * Produce enhanced DTMs (better than any of the inputs) * Update DTMs based on temporal changes * Good test case (Slovenia has interesting terrain and a wide variety of available data sources) * Drawbacks possible when integrating data from a variety of sources: * Lowest common denominator * Inconsistencies in accuracy across DTM * Possible solutions: * Multi-resolution approach (referenced but not described) * Produce multiple DTMs depending on area * Describes methods of removing gross errors, but requires reference with "high and known quality" -- thus several DTMs can make a DTM better than any of the components, but at least one must be realtively good ---++ References * [1] Podobnikar, T., Production of integrated digital terrain model from multiple datasets of different quality, _International Journal of Geographical Information Science_, 19:1, January 2005, pp. 69-89. ---++ Slovenia Links * http://europa.eu.int/abc/maps/index_en.htm -- map of the EU with Slovenia * http://www.gumbopages.com/festivaltours/ljubljana.html -- a picture of Ljubljana, the capital of Slovenia * !http://www.bled.si/slo/narava/otok/jezero.jpg -- sample picture of lake and mountains -- Main.HenryMcEuen - 03 May 2005
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