Building Photorealistic Virtual Outcrop

A photorealistic outcrop is derived through the processing of texture mapping which glues the photograph of that outcrop on the terrain surface. The outcrop photographs taken by geologist in the field are generally highly oblique and also subject to camera distortions (such as radial and tangential distortion). The process of capturing outcrop photographs is actually a process of projecting outcrops into image planes through the camera lens.

A photorealistic outcrop was created from an outcrop of the Cretaceous Austin Chalk in Dallas, Texas the Post Office Service Bulk Mail Station. Geologic contacts, faults, random topographic points and topographic breaklines were surveyed with an RTK GPS controlled reflectorless total station. The terrain surface was modeled through a constrained triangulation mesh. The pictures of outcrop were taken by Olympus D-600L digital camera at resolution of 1280X1024 pixels.

The whole outcrop is captured digitally and can be carried back to the office for further study. The generation of a photorealistic "virtual" outcrop allows a user to "walk through" the virtual outcrop on the screen of a computer or in real scale in an "immerse virtual environment". The outcrop surface could then be lifted so the user can see the associated subsurface geology from wells and geophysics and by projecting the surface data into the subsurface. On-screen digitizing on the photorealistic outcrop provides true three-dimensional coordinates of features, a new way to quantitatively capture additional geologic information after returning from the field. Some examples are shown below.

This example has been successfully imported and viewed in ARCO Exploration and Production Co.'s 3D immerse visuluatization enviornment "CAVE".

The original survey points at Dallas Bulk Mail station outcrop displayed in 3D. Two of the key beds are in yellow color, the faults in red. The natural breakline in terrain also shown.

The terrain surface fit through the above points. In order to define the natural break of the surface, this terrain surface consists of three parts: the top, bottom and cliff . The model was done in GoCad.

This figure shows the mosaic of two photos in 3D. The photos were taken in different times of the day so the color pattern is different. The algorithm we used for the image registration yields subpixel accuracy as is the case in these two photos.

Above photos show our photorealistic outcrop viewing at different angles. A total of five photos were taken of this outcrop, registered, and texture mapped onto the terrain surface.

Note that some of the point sets defining geologic features were generated in the field by direct laser mapping while others were extracted by direct digitizing of the resultant virtual outcrop back from the field.

3d model of key bedding and fault surfaces

Different views of the virtual photorealistic 3D outcrop.