CMRT09

Stilla, Uwe

Bibliographic data

Monograph

Persistent identifier:: 856955019

Author:: Stilla, Uwe

Title:: CMRT09

Sub title:: object extraction for 3D city models, road databases, and traffic monitoring ; concepts, algorithms and evaluation ; Paris, France, September 3 - 4, 2009 ; [joint conference of ISPRS working groups III/4 and III/5]

Scope:: X, 234 Seiten

Year of publication:: 2009

Place of publication:: Lemmer

Publisher of the original:: GITC

Identifier (digital):: 856955019

Illustration:: Illustrationen, Diagramme, Karten

Language:: English

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2016

Document type:: Monograph

Collection:: Earth sciences

Chapter

Title:: ROAD ROUNDABOUT EXTRACTION FROM VERY HIGH RESOLUTION AERIAL IMAGERY M. Ravenbakhsh, C. S. Fraser

Document type:: Monograph

Structure type:: Chapter

CMRT09: Object Extraction for 3D City Models, Road Databases and Traffic Monitoring - Concepts, Algorithms, and Evaluation of parameters for roundabouts are derived. Second, the central island is extracted using a level set approach making use of prior information obtained from the previous step. Finally, the roundabout is reconstructed using a snake-based method. The proposed approach has the aerial image, a topographic database and the road arms as input, and the roundabout border connected to the existing road arms as output. The reader is referred to Ravanbakhsh et al. (2008) or Ravanbakhsh (2008) for a description of how the road arms are extracted. 3.1 Pre-analysis of topographic database Roundabouts are usually represented in topographic databases in one of two ways, either as an area object when the diameter of the inscribed circle is larger than the threshold (Fig. la), or as a point object when the diameter of the inscribed circle is small (Fig. lb). The actual representation threshold varies in different topographic databases. This vector data is used to focus the extraction process to the image regions where roundabouts are located. Furthermore, the approximate diameter of the central island and width of the circular roadway can be initially determined (Fig. 3). It is noteworthy that the width of the circular roadway depends mainly upon the number of entry lanes. The width of entry lanes is also derived from vector data. According to construction standards, the roadway must be at least as wide as the maximum entry width and generally should not exceed 1.2 times this width (U.S. Federal Highway Administration, 2000). In case that a roundabout appears as a point object, attributive information must be included in the topographic database implying that the node represents a small roundabout. This means that the diameter of the inscribed circle is below the threshold that has been defined in the topographic database. 3.2 Central island extraction With roundabouts, a correct extraction of the central island helps facilitate the extraction of the outline. The reason for this is that the central island, when enlarged, influences the shape of the roundabout outline. The initial detection of the central island can then provide a good idea of how the outline appears in the image. The proposed method to detect central islands is based on level sets. Geometric active contours were introduced by Caselles et al. (1993) and Malladi et al. (1995). These models are based on curve evolution theory and the level set method. The basic idea is both to represent contours as the zero level set of an implicit function in a higher dimension, usually referred to as the level set function <f>, and to evolve the level set function according to a partial differential equation (PDE). It is well known that a signed distance function, a function which introduces the minimum distance from every point in a defined domain to the zero isocontour of a level set function, must satisfy the desirable property of |V^ |=1 (Osher and Fedkiw, 2002). The following formula has been proposed to provide the internal energy of a snake which penalizes the deviation of (f) via a signed distance function (Li et al., 2005): m= f Liv<ii-ifdxdy (i) 2 is a metric to characterize how close the function (f> is to a signed distance function in a specified computational domain Qc R 2 . The external energy is defined by E m ((/>) = AL g {(f)) + v A g {(f>) (2) where /i>0 and v is a constant and the length termL^ area term A g (<j)) are defined by (^) and L g ((/)) = gS(<f>) | V (f> | dxdv (3) A g (</>) = J Q gH (-(f)dxdy (4) with the edge indicator function g being given by 1 g= , (5) 1+|VG CT */1 2 Here, H is the Heaviside function, 8 the univariate Dirac function, G,j the Gaussian kernel with standard deviation cr , and / image intensity. INPUT DATA PROPOSED APPROACH RESULT Roundabout area Road arms Roundabout Roundabout border | Central area Central island (a) Figure 2. (a) Roundabout model and (b) workflow of roundabout extraction. 20

Access restriction

Copyright

fullscreen: CMRT09

Monograph

Chapter

Table of contents

Cite and reuse

Monograph

Chapter

Image

Image fragment

Citation links

Citation recommendation