Visibility analysis of point cloud in close range photogrammetry

Abstract

Commission V, WG V/2 KEY WORDS: visibility -point cloud -voxel -HPR -line tracing -z buffering ABSTRACT:The ongoing development of advanced techniques in photogrammetry, computer vision (CV), robotics and laser scanning to efficiently acquire three dimensional geometric data offer new possibilities for many applications. The output of these techniques in the digital form is often a sparse or dense point cloud describing the 3D shape of an object. Viewing these point clouds in a computerized digital environment holds a difficulty in displaying the visible points of the object from a given viewpoint rather than the hidden points. This visibility problem is a major computer graphics topic and has been solved previously by using different mathematical techniques. However, to our knowledge, there is no study of presenting the different visibility analysis methods of point clouds from a photogrammetric viewpoint. The visibility approaches, which are surface based or voxel based, and the hidden point removal (HPR) will be presented. Three different problems in close range photogrammetry are presented: camera network design, guidance with synthetic images and the gap detection in a point cloud. The latter one introduces also a new concept of gap classification. Every problem utilizes a different visibility technique to show the valuable effect of visibility analysis on the final solution.

Strategies to Evaluate the Visibility Along an Indoor Path in A Point Cloud Representation

“…A commonly used approach to evaluate the visibility from a certain point of view is that which perform the generation and the subsequent interrogation of a synthetic image. A synthetic image is a digital map, in which the pixel values are the coordinates (x, y, z) instead of the RBG information (Alsadik et al, 2014). Alsadick et al (2014) describe a technique for generating synthetic images based on the method of Zbuffering.…”

Evaluation of Driver Visibility From Mobile Lidar Data and Weather Conditions

“…Alsadik et al (2014) summarize techniques for visibility analysis grouped on triangulation approaches, voxel approaches, and hidden point removal. Yin et al (2012) review some visibility techniques based on sight calculations and projection methods.…”

“…The visibility analysis is based on a ray-tracing algorithm, which consist on creating a Line of Sight (LOS) from one point to an objective point, and check the obstacles causing occlusions between the beginning and the end of the line (Alsadik et al 2014). The LOS starts in the position of the driver eyes, estimated at 1.1 m above the car trajectory on the road surface (Ministerio de Fomento, 1999) and continues in the direction of the car trajectory.…”

Interurban visibility diagnosis from point clouds

“…For instance, Alsadik et al [2014] study different techniques for visibility analysis with point clouds obtained from photogrammetry [Rothermel, et al, 2012], showing the differences between the techniques and their pros and cons. They summarize techniques for visibility analysis in three groups.…”

“…In addition, extract the road from the point cloud will help the workflow by defining afterwards the trajectory of the vehicle with this road section. After that, a ray-tracing algorithm is implemented to calculate visibility in the Line Of Sight (hereinafter referred as LOS) [Alsadik et al, 2014;Previtali et al, 2014] between car and pedestrian/cyclists, taking the theoretical position of driver eyes as the starting point of the LOS. The LOS is rotated on the vertical axis, taking into account the trajectory of the vehicle and the field of view of the driver.…”