Building Creation and Rendering

From Plan to Wireframe | Material Preparation | From Wireframe to Finished Model

From Plan to Wireframe

This document is a detailed description of the full process employed to build an AutoCAD model of a building and then complete a photo-realistic rendering of that building. For illustrative purposes, images of the Monastery of Constantine Lips will be presented at various points throughout the document.

Lips Monastery

The first step in the creation of a completed building model is the construction of a 3-d wireframe model using AutoCAD. For most of the Byzantine structures still extant in modern Istanbul there are a variety of bibliographical sources which contain, along with abundant historical information, plans and elevations of the structures in varying degrees of detail. In the case of the current project, these drawings were supplemented by measurements made in the field during the spring of 1995.

Measured Drawings

There are various methods of constructing models in Autocad. We have found that the easiest and most applicable method employs the solid modeler included with AutoCAD Release13 (known previously as the AME solid modeler). This method utilizes the boolean operations subtraction and union. Using simple 3d objects such as boxes, cylinders and spheres, more complex domes, vaults, and windows can be created. With those three elements, along with standard straight wall, floor, roof sections, and columns (AutoCAD cylinders) almost all of the structures being studied can be accurately modeled.

There is also a question as to what degree of detail is necessary in the model, and what can be left up to the capabilities of the texture mapping software. We feel that much of the detail work is easier to achieve using texture mapping rather than creating excessively complex AutoCAD models. Clearly, all vaulting, domes, walls, etc must be modeled accurately. It is probably unnecessary, however, to model objects such as column capitals and relief work. For the most part we have found that a great deal of detail can be added to a model through the use of well conceived and executed photographs in the texture mapping process.

At the completion of this stage, the entire geometry of the building has been laid out. AutoCAD provides the ability to view this model from various angles, with hidden geometry, and a rough rendering, without texture maps.

Completed AutoCAD Model

Material Preparation

This is perhaps the most critical stage in the journey towards a photorealistic rendering. In order to create a convincing effect on the finished model, materials must be prepared from photographs in such a manner as to make mapping possible.

The first step in this stage is the actual taking of photographs. This is critical, for without consistent, perspectiveless photos, materials cannot be made convincing. For large expanses of wall and roof, we have found the most effective method involves repeating (in a tiled pattern) a relatively small photographic sample of the brickwork in order to fill the large area.

Sample Brick Photos

This can create a very convincing effect, but is highly dependent upon the quality of the photos. The photo must be taken directly facing the wall, with a a lens that will not create any wide angle distortion, and with as even lighting as possible. These requirements ensure that there will be no patterning of angle, or light and dark within the sample that will become obvious when the pattern is repeated to fill a wall.

As stated earlier, a relatively low degree of detail need be included in the AutoCAD model, and a great deal of "apparent" detail can be added by appropriate use of photographs. For example, effects such as windows with mullions and transparent panes can be achieved. Additionally, the trim around windows can be effected by use of an overview photo, rather than actual modeling.

After all materials have been prepared, the wireframe model can be imported to 3dStudio, and the texture mapping can begin.

From Wireframe to Finished Model

The final step and most exciting step towards a finished model is the application of prepared photographic materials to the wireframe model. This stage requires great familiarity with the materials editor of the software package 3dStudio (an application which allows the photographs prepared in the previous step to be actually applied to the structure). The process is immensely powerful and actually fairly simple to employ.

In the materials editor the photograph, prepared using Photoshop, is specified as the texture map for a newly created material. In addition to textures, photograph files can also be used as bump and opacity maps to create the truly textured and transparent surfaces previously described.

In order to make an object actually appear mapped, two things must be done to it. First, the prepared material must be assigned to the object. Second, because the material has a pattern to it, coordinates must be assigned to the object which specify in what orientation and at what scale the photo is to be applied. By following these two steps, photographs can essentially be "pasted" on to all of the walls, domes, and vaults in the building. From the plans and elevations, we have progressed to the point where exterior and interior views are possible, and, if we have accomplished what we had hoped to, one feels as if he or she is looking at a view of the actual structure.

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