Smooth string file
The contours produced by the CONTOUR EXTRACT function are the most accurate representation based on the data from which the DTM was formed. However these contours can be quite angular, reflecting the triangulated surface from which they were derived.
To run this function: Choose Surfaces > Contouring > Smooth string file, or...
Two techniques are provided to allow you to smooth these contours for a more aesthetically pleasing result. It must be stressed, however, that any smoothing technique generates new data points mathematically, and these may not exactly honour the original data as do the original contours.
This can result in:
- crossed contours after smoothing
- data points on the wrong side of smoothed contours if both the smoothed contours and original data points are plotted together.
The two techniques available are:
- simple cubic interpolation between points
- cubic spline curve fitting to contour points.
For cubic spline curve fitting, you simply nominate how many sub-segments you want each contour line segment divided into. (Thus smoothing results in an increase in data points by this factor, although resulting line segments less than 0.01 world data units long are discarded!)
The `interpolation' option retains all the original points, and adds additional points between. While this smooths individual contour line segments, there may not be a `smooth' transition between line segments; only contours with four or more points will be smoothed.
Whenever one of these smoothing techniques is used for presentation plots, you must check the resulting plot to make sure it is sufficiently accurate for your requirements.
Because of the increased number of data points in smoothed contours, plotting can take considerably longer.
Fields on the SMOOTH CONTOUR STRINGS form.
Define the string files to be smoothed
Identify the range of string files to be smoothed by entering a Location and ID range.
Define files to contain smoothed strings
Enter the Location code for file(s) to receive the smoothed strings. They will have ID's to match the input files.
Number of lines per segment
Enter the number of line segments to be generated for each line segment in the original strings, in the range 2 to 10. Again, the best value depends on you and the data, but remember your amount of data will expand by (up to) this factor!
(S)pline or (I)interpolation smoothing
Enter S or I to select from the two smoothing techniques described earlier. The more appropriate technique depends on the data being smoothed and the use to which the smoothed contours will be put.
Retain descriptions
New points generated while smoothing have interpolated X, Y and Z values, but nothing is done to the Description field. If you respond N to this question, Description fields will not be transferred to the `smoothed' files. If you answer Y, the option assumes the Description field is the same for all points in a string or segment and the Description from the first point is copied to all points of the smoothed string or segment.