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In the early days of cave surveying, the LRUD measurements were used primarily to assist in hand-drawing maps. For this reason, the data-collection standards were loose. Now that we have computers to process the data, we can create realistic passage models. However, because of the way we collect data, the quality of the models is less than ideal. Here are some of the issues.
Sparce Data. Most surveyors only take passage measurements at the survey stations. For this reason, the passage models will miss any variations in passage size that occurs between stations. The problem is worse on large passages where the shots may be over 30 meters in length. One solution to this problem is to take shorter shots.
Missing Data. In many caves, LRUDs are not collected. If the no passage dimensions are specified in the survey file, the program cannot display passage walls. If no passage dimensions are present, the program will simply display a straight line. COMPASS can fill in for missing data by substituting the dimensions from nearby passages. However, this is only a cosmetic fix.
Vertical Passages. As passages get steeper, the standard definition LRUDs ceases to have meaning. For example, in a vertical pit, the Up measurement would measure the depth of the pit instead of the passage shape. At this point in time, there is no standard for measuring the passage dimensions of a vertical or near-vertical passage. However, COMPASS offer the options of treating the LRUDs of steep passages as West, East, North and South directions respectively. Click here for more information.
Speed. Also, passage modeling slows the drawing time dramatically. The more complex the option, the slower the draw speed. For example, unfilled polygons draw much faster than shaded polygons. This is not much of a problem on a small cave, but with a large cave it can take many seconds to draw the whole cave. Remember, that as you zoom into the cave, drawing gets much faster, even when your are drawing passage walls.