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CS TH - Contour Storage - THinning

(12/29/93)

PURPOSE

Thins contours in a contour storage file. Allows the user to decrease the number of points on a contour in a manner that has minimum effect on the shape of the contour. Thinning also decreases storage space and plotting time.

SEE ALSO

CS DI PL [Contour display - convert to HPGL]
CS DI PO [Contour display - convert to Postscript]
CS DI TX [Contour display - on Tektronix 4662 plotter]
CS DI VT [Contour display - on VT125/240 terminal]
CS MV [Contour Storage - transfers to MOVIE.BYU format]

USAGE

.OPERATION: CS TH

.CONTOUR FILE: CNT001
[Enter the name of the file of interest.]

.DO YOU NEED THINNING CUTOFF DATA FIRST: (Y/N): Y
["Yes" gives a summary of the minimum and maximum line lengths and maximum interline angles for adjacent line segments which occur in the contour file. This data is useful for specifying the thinning parameters.]

.DO YOU WANT TO OK EACH CONTOUR THINNING: (Y/N): N
["Yes" allows one to reject the thinning which is performed on each contour. This is useful to avoid over thinning a contour and altering its shape excessively. A "No" answer will automatically thin all of the contours based on the thinning parameters and replace them in the contour file.]

If "Yes" next question appears.

.DO YOU WANT TO VIEW EACH CONTOUR? (Y/N): Y
["Yes" will plot each contour on a DEC graphics terminal before and after the thinning. Over thinned contours can then be rejected below.]

The thinning parameters are now requested.

.ENTER MIN LENGTH FOR RETAINED LINES: 0.01
[Any line segment shorter than this limit will be deleted from the contour.]

.ENTER MAX LENGTH FOR NEW LINES: 0.1
[However, if deletion of a line segment results in a new line segment longer than this limit the segment will not be deleted.]

.ENTER MAX ANGLE BETWEEN RETAINED LINES (NEAR 180): 179
[Adjacent lines segments which have an angle between them greater than this limit are merged into a single line segment. E.g. all pairs of line segments separated by angles greater than 179 will have the beginning point of the second line segment deleted so as to from a new longer line. However, thisdeletion is subject to the restraint requested in the previous question.]

.ENTER MIN. SIZE CONTOUR TO BE THINNED: 8
[Any contour shorter than this limit is not thinned at all. E.g. contours less than eight points long will not be thinned.]

The length of each contour before and after thinning is then listed. The contour is displayed if the user has asked to view them and the following question appears.

.0.K. TO STORE THIS THINNED CONTOUR? (Y/N): Y
[A "No" answer aborts thinning of this contour and following question appears.]

.CHANGE THINNING PARAMETERS AND TRY AGAIN? (Y/N): Y
[Allows the user to alter the minimum and maximum lengths and angle which have previously been input and attempt to thin the contour again using these new parameters.

NOTES

  1. WARNING: THIS PROGRAM ALTERS THE FILE. AS A PRECAUTION YOU SHOULD CREATE A BACKUP COPY OF THE FILE.

SUBROUTINES

CNTHIN

CALLER

PLOT1

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