## Three Dimensional Passage Modeling

Passage modeling is an approximate method to help visualize a cave's complex nature. Because of the limited nature of the passage diminesions, in the form of Left, Right, Up and Down (LRUD) measurements, only crude drawings can be made. Obviously, the more junctions and rooms a cave survey has, the more difficult it is to describe in a finite set of measurements.

In the sample drawing above, the left and right measurements at A4 adequately describe the passage topology. At station A5 the passage splits left and right. Often, when confronted with this situation, surveyors mark "P" for passage for the left and right measurements at A5. In this case, WinKarst subistutes the survey's average passage dimensions for left and right. The assumption is the average survey dimensions are localized and characteristic of the passage in the vicinity of A5.

The other problem with A5 is which direction is left and right? WinKarst uses two shots to define a left or right direction. In the case of a junction, all of the directions are rights. The shots A5 to A4 and A5 to A6 define a pair of shots and the bisection of the angle created by the pair is the right passage dimension direction. Similiarily, the shots A6 to A5 and A5 to C1 define a pair and C1 to A5 and A5 to A4 define another pair. At station A5, there are three passage dimensions and they create the triangle around the station. A another triangle is formed at A6. Should a junction contain four shots, then a four sided polygon will inclose the station and so forth for more complex junctions. Should there be more than one LRUD measurement at a station, they are averaged for the drawn representation.

The shots C1 to C2 and C1 to C3 are an example of a typical inaccuracy. WinKarst does not check whether two adjacent wall sections overlap or not. In this case the solution, assuming the left and right measurements at C2 and C3 are correct, is to shoot an intermediate station mid way along both shots. In general, the more and shorter the shots in a cave survey, the more accurate the passage model will be.

The drawing above shows how a wire mesh for a cave passage is created in WinKarst. In this example, the passage's vertical dimensions, up and down, were held to a constant value and flat for simplicity and its basis was the drawing at the beginning of this page. The two wall components for a shot are vertical rectangles. The floor and ceiling for a shot are two triangles each. In general, the floor and ceiling are formed this way because twisting of the passage prevents these plates from being drawn by a simple planar rectangles. The triangles at the junctions C1, A5 and A6 are modeled with flat floors and ceilings.

Final three dimensional rendering after exporting the passage model to a third party graphics program. Press here to see a VRML view of the same drawing (note, you must have a VRML plugin installed in your browser, which are free from MicroSoft or Netscape).