PART VI: GRID INTERPOLATION PROGRAM (INTPRCP) 

 General Comments 



106. Bathymetry at every cell of the finite difference grid mesh is re- 

 quired as input into RCPWAVE. Since digitization of bathymetric data from 

 survey or nautical charts is both tedious and time consuming, it is desirable 

 to limit the number of times one must perform this task. The grid interpola- 

 tion program INTPRCP provides a method for determining bathymetry on a "new" 

 grid using depth data from an "old" grid. The origin of the new grid can be 

 rotated and/or translated relative to the old grid origin. This capability 

 for interpolation ensures that the bulk of the digitization is done only once. 

 The program is useful when: 



a. A coarse grid containing bathymetry is available but finer 

 resolution is desired or required. 



b. The axis orientation of the available grid is different from 

 the desired orientation. 



c. The region to be modeled is a subset of the available grid. 



A compiled listing of the program is given in Appendix I. 



107. The program uses a fairly simple interpolational scheme. For each 

 new grid cell, a search is done for the nearest old depth value in each of the 

 four 90 deg quadrants relative to the new cell center. A weighted average of 

 these four values is used to compute a new depth. The weighting functions are 

 based on relative distances from the new grid center to the cell centers de- 

 fining the positions of the four old depth values. 



108. JCL is available to run the program on the CDC CYBER 205 machine 

 only. The next section briefly describes the procedures performed in the 

 course of job execution. It also explains how an interpolational job is sub- 

 mitted. The third section documents, in detail, all required input files and 

 includes some examples. It also describes the output files created during 

 program execution. A complete example illustrating the use of INTPRCP is 

 presented in the last section. 



Executing INTPRCP on the CDC Computing System 



109. The interpolation program is run on the CYBER 205 machine in a 



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