טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentClaudio Osengar
SubjectA CAD Model for Evaluating the Shading of Buildings by
Various Elements
DepartmentDepartment of Architecture and Town Planning
Supervisor Professor Emeritus Shaviv Edna


Abstract

The present study focuses on the shading of the building in summer and its exposure to the sun in winter, and examines the mutual shading affected by other objects in the project. To achieve this purpose a computerized model “SE-MODAT” for shading evaluation was developed, which combines with existing CAD softwares for modeling and renderings. The model comprises two models: “SE” (Shading Evaluation), and “MODAT” (Modeler Data Transfer).


The model “SE” facilitates the evaluation of mutual shading on and in between buildings and various objects in the area. Fast and efficient evaluation of complex projects which contain numerous elements can be made, owing to the use of an algorithm which utilizes the advantages of modern work stations, such as SGI. It is possible to evaluate bodies of any form, evaluate the shading one or several planes concurrently or carry out different evaluations of the project using the same data base in different sections and combinations. These evaluations can be made during any design stage and be displayed visually from the sun’s viewpoint or from a free viewpoint with a projected shadow, and produce a quantitative output. In a “Fast Visual Evaluation” from the sun's viewpoint the project is displayed in an orthogonal projection with the elements shown on the screen exposed to the sun, and the unseen ones are shaded. A “Realistic Visual Evaluation” with a cast shadow is made by existing renderer models, such as “Radiance” or “ISM”, which provide realistic pictures of the examined project with a projected shadow, calculated by existing algorithms of “Radiosity” and “Ray-Tracing”. The use of strong graphic work stations such as SGI facilitates making quantitative evaluations, using the “Bitmap” system while using to good advantage the “Z-Buffer” and the “Double Buffer” available in these stations. Consequently it is possible to calculate the percentage of shaded area (GSC) and percentage of exposed area (GIC) of any planes and the weighted geometrical coefficient of shading area and exposed area to the sun (WGIC, WGSC), with the weighting depending on the sun ray’s angle of incidence with the examined plane at the examined hour. With this quantity one can easily determine the quantity of energy arriving at the examined plane is a window. This method also facilitates the fast and easy evaluation of partial shading caused by objects like tree crowns, drapes of certain fiber density, blinds made of specific slats, etc.


The “MODAT” model allows the integration between modeling models, evaluation models and rendering models by means of a translator model. “MODAT” allows also to edit new primitive bodies by means of an modeling model, which is part of it. The Input Data Transfer model enables to receive a geometry built by commercial software, such as “AutoCad”. The editing and modeling model enables to introduce the necessary changes into the geometry of the project made by “AutoCad”, or into the new bodies added to the same project. The model enables to work and store objects in a hierarchical order, by layering the bodies and storing the body data generically by means of meshes, while maintaining the hierarchical order set by the “AutoCad”. Thanks to the hierarchical order it is possible to make various evaluations on the same data base that makes up the project and to make hierarchical evaluations as well.


To solve the problem of objects which provide partial shading, like trees, a computerized system for the interpretation of tree crowns was developed in the course of this study. The model which was developed for the modeling and evaluation of tree shading, “GD-TREE” (Geometry and Density of Tree), enables to receive by means of an algorithm developed in this study the accurate density and geometry of a tree crown. The system is based on digitalization of tree photographs which enables to define the silhouette and background of the tree crown, and consequently to calculate the trees density and to work out the three-dimensional form. The geometry and density of the tree crown data are fed to the model for shading evaluation “SE MODAT” parametrically by entering minimal data. The display of trees in the model is carried out by revolution bodies composed of a thee-dimensional mesh, whose outline is determined by the tree crown's silhouette and whose profile is made of the geometry that emerges in the model. The density of the tree determines the density of the texture and coloring of the tree’s picture which is projected in the perspective picture. The “MODAT” model also enables to input the data of the sun’s position, of the eye's position and the target’s position as well as the data base of the project geometry to display models, such as “Radiance" or "ISM”, and enables to input the “GIC” into a simulation model “ENERGY” that carries out an evaluation of the thermal behavior and illumination of buildings. In order to examine the applicability, accessibility, scope and result verification of the model, it was tested on two complex projects. The model proposed for editing and evaluation of tree’s shading was tested and illustrated on a case of a deciduous tree.