Line of Sight Calculation as a Service
Author
Pedersen, Jonas Nygaard
Term
4. term
Publication year
2016
Submitted on
2016-06-15
Pages
71
Abstract
This thesis examines how to compute visibility as a line of sight between two points and deliver it as a standards-based web service. The solution is implemented as a custom PL/pgSQL function inside a PostgreSQL/PostGIS database that stores elevation as raster data, using trigonometric calculations and compensating for Earth curvature. The functionality is exposed through the OGC Web Processing Service (WPS) using the ZOO-Project so it can be readily consumed by web mapping libraries, with clearly defined input and output formats. Methodologically, the work includes selecting and preparing data, constructing a line between observation and target points, sampling raster elevations along the line, calculating angles to classify visible versus non-visible points, and producing GeoJSON results. Accuracy is evaluated by comparing results with orthophotography, the source DEM, a 3D model, and on-site photography, while performance is compared across alternative implementations. Finally, the potential value of line-of-sight analysis as a parameter in a standardized, modular framework for property/housing taxation is discussed. (Note: Specific accuracy and speed results are not provided in this excerpt.)
Specialet undersøger, hvordan synlighed kan beregnes som en sigtslinje mellem to punkter og stilles til rådighed som en standardiseret webtjeneste. Løsningen implementeres som en skræddersyet PL/pgSQL-funktion i en PostgreSQL/PostGIS-database med højdemodeller som rasterdata og inddrager trigonometriske beregninger, herunder korrektion for jordens krumning. Funktionaliteten udstilles via OGC Web Processing Service (WPS) med ZOO-Project, så den kan forbruges direkte af webkortbiblioteker, og der defineres klare input/output-formater. Metodisk omfatter arbejdet udvælgelse og forarbejdning af data, opbygning af en linje mellem observations- og målpunkt, sampling af rasterhøjder langs linjen, beregning af vinkler for at afgøre synlige og ikke-synlige punkter samt generering af GeoJSON-resultater. Præcisionen vurderes ved at sammenholde resultaterne med ortofoto, det oprindelige DEM, en 3D-model og et on-site foto, mens ydeevnen sammenlignes på tværs af alternative implementeringer. Endelig drøftes den potentielle nytte af synlighedsberegninger som parameter i en standardiseret, modulær ramme for ejendoms-/boligbeskatning. (Bemærk: De konkrete præcisions- og hastighedsresultater fremgår ikke af dette uddrag.)
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