docHydrological Conditioning TerraSTREAM: Hydrological
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Hydrological Conditioning TerraSTREAM: Hydrological
Morten Revsbæk University of Aarhus University of Aarhus TerraSTREAM: Hydrological Conditioning TerraSTREAM: Hydrological Conditioning Hydrological Conditioning and Flow Routing Motivation Problem: Detailed data set g g g •Fghfghfghf Calculating Persistence •fghfghfghfghffffffffffffffffffffffffffffff g g g g ffffffff Many small, small insignificant sinks. sinks Flow Routing Consequence: Disconnected river network. Flow Routing Solution: Sol tion Find insignificant sinks and remo remove e them them. Th The graph h tto th the right i ht shows h b both th th the h i ht and height d th the volume l off each h sink i k (red ( d cross)) iin the th tterrain i d depicted i t d below. b l Th The red d river i network t k is i generated t d from f the th h height i ht conditioned diti d terrain. t i Insignificant Sink g The Vertical line represents p the height g threshold that removes all but the three highest sinks. The blue river network is generated from the volume conditioned terrain. The Horizontal line represents the volume threshold that removes all but the th three llargestt sinks. i k Conclusion: Blue network is connected in the purple circles i l and d the th flow fl is i more “ t l” iin the “natural” th bl blue circles. i l Contour Line Consequence: Many small and insignificant contours. Significant Sink g Solution Conditioning and Contour Line Generation We associate a numeric value – persistence value - with each sink. Persistence P i t value l can be b the th height, h i ht area or volume l off sink. i k Define a p persistence threshold and remove all sinks with a persistence value lower than the threshold. p Contour Lines The top right terrain has been conditioned using height persistence persistence. W We can enhance h the th output t t off contour t liline generation, ti b removing by i sinks i k that th t result lt iin iinsignificant i ifi t contours. t Th The bottom b tt right i ht terrain t i has h b been conditioned diti d using i volume l persistence. i t Big Height Big Area Removing g Sinks The thresholds used are the ones given in the graph above, so that in each of the terrains only three sinks are kept after conditioning. g Volume Big Conclusion: The sinks kept when h using i volume l conditioning diti i seem much h more significant i ifi t and d i t iti l they intuitively th correspond d to t the th sinks i k that th t water t will ill realistically li ti ll fl flow towards. t d I/O Effi i t Algorithm I/O-Efficient Alg ith Hydrological conditioning using height persistence can be done I/O-efficiently I/O efficiently using I/O-efficient I/O efficient batched union-find union find as proposed by Agarwal, Arge and Yi in 2006 [SoCG [SoCG’06] 06] W We d defined fi d and d solved l d th the more generall batched b t h d union-find i fi d with ith d dynamic i sett properties ti so that th t both b th height, h i ht area and d volume l persistence i t (or ( any combination bi ti off these) th ) can b be calculated l l t d I/O I/Oefficiently. ffi i tl Black contour lines were generated from a terrain conditioned using volume persistence. Red contour lines were generated t d ffrom a terrain t i conditioned diti d using i height h i ht persistence. i t In the top p figure g the black lines have been drawn on top p of the red lines and vice versa in the bottom figure. g Conclusion: Volume persistence removes many insignificant contours (top) that are kept when using height persistence, persistence whereas h i ht persistence height i t removes contours t th thatt seem significant i ifi t (bottom). (b tt ) MADALGO – Center for Massive Data Algorithmics, a Center of the Danish National Research Foundation MADALGO – Center for Massive Data Algorithmics a Center of the Danish National Research Foundation
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