Building 3D Digital Models For Cities in Large Topographic scales in GIS

3D GIS can be realized as an actual building platform of the urban space. This research develops automated 3D urban models that fit large-scale digital photogrammetry. Originally, modeling used manual or semi-manual techniques, and there is a need to for a development of an approach that automates the transformation of vector linear data, optimized by digital photogrammetry stations to create the 3D volume model in 3DGIS. This approach consists of three main phases: roof modeling, wall modeling and volume structuring. During the first phase, local and conditional "Delaunay Triangulation" method is used to deal with the majority of roof types regardless of its geometry. The second phase is completely automated to create the walls by the vertical projection (Top-Down) of the outer line of the roof into the Digital Terrain Model (DTM), and then by the selection of the bottom base level as the default level. Finally, different elements of the structure can be aggregated using spatial relationships (many-to-many) already supported by GIS software. The new approach is created and completely automated. It doesn't require roof geometric-types library, which asserts the GIS is a valid platform to build, to view and to store 3D urban models.

Lidar Techniques and Applications in Detection of some Gaseous Pollutants (Review)

This review aims to show the techniques of lidar in atmospheric remote sensing, which can be utilized to draw three-dimensional maps of pollutants distribution over path lengths of the order of few kilometers. The detection limits achieve values of the order of ppb. This sensitivity and accuracy gives this method its superiority over all other physical and chemical methods of detection. Some details of this method are given for the following pollutants: NO, NO2 , SO 2, O3, HCl, C2H4, benzene and toluene, as well as atomic mercury. This work shows, for these pollutants, absorption wavelengths, differential cross sections and detection limits. In addition to dealing with the technical requirements and different designs of Lidar. On the other hand, this review study handles the characteristics of many laser sources used in lidar systems such as, Nd:YAG- laser, Dye- laser and others. Especially it concentrates on pulse energy, time duration, repetition rate and nonlinear crystals, used for frequency doubling, which broaden the working region of the lidar.