It is sometimes necessary to survey tree canopies more accurately by recording the spread of the tree in more than one direction. The International Standards Organisation defines that four spreads should be recorded and these should be at the four main compass points from the centre of the tree bole. If attribute check button ISO Tree Canopy is checked, it is assumed that this is what has been surveyed.
Each point where a tree canopy is to be produced is assumed to have a Tree Canopy dimension, TC=. The dimension string is a comma separated string of the four spreads starting at north and proceeding clockwise around the point, thus taking the form TC=N,E,S,W. The line that is produced at each point is a 4-point curve fitted polygon and there is no line connecting the points along the feature.