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Basic Information

Name of Program



December 2013


December 2013


finite differences methods
grid generation
distribution of land and water

Short Description of Functionality

The program FD2BASIS generates a FIDISOR/FIDIRB grid with correct distribution of land and water areas. The latter is constructed from digitized boundary structure lines like the high water boundary ( simulations of normal tidal situations) or dike line (for storm surge simulations).


  1. input control file (type fd2basis.dat)
  2. one or more files with digitized boundary structures (type digi.gkk)


  1. basic FIDISOR/FIDIRB grid (type topo.bin)
  2. file randpkte.dat with boundary cell indices and the intersecting polygon part (is used internally for boundary fit).
  3. buffer files liste_1.dat and liste_2.dat
  4. printer file fd2basis.sdr
  5. (optional) trace file fd2basis.trc


First a matrix IPOLY is allocated with given grid dimension which contains 0 overall. Then all cells which are touched by the given boundary structures are set to the values 99 or 98 (fix point or interpolated point respectively). Now land is initialized with -99, beginning with the landpoints given by the user. If a cell is reached, which has a value different from 0 the search continues in another main direction or at the next landpoint. All initialized land cells become starting points itself. For purpose of memory saving parts of the starting points are buffered on disk.

Last step is the correction of the boundary points. If the area of land inside the cell is greater than that of water, the cell is set to land. The area is calculated from the intersection polygon, which was stored in randpkte.dat.


  • The structures can be stored as parts and there is no need of sorting before using this program. The only constraint is that they must in total represent closed structures (islands) or their beginning and ending shall both lie outside the grid area. Holes in a boundary can lead to unwanted results!
  • A structure which contains only one point is ignored. Double points following each other are used like one point.
  • A manual postprocessing can be neccessary for thin areas of water or land (land connections, small channels) if resolution of the grid is not high enough to resolve theese structures.
  • Coordinates of raw data files are now transformed to a user defined coordinate reference systen (CRS) if necessary. To support this feature, the user must include a magic comment with the content "C CRS=xxxxx" at the beginning of the file. Here "xxxxx" stands for the EPSG code of the CRS. Additionally the user has to set the environment variable BAWCRS to a valid CRS. All Input files of type topo.bin must be realized in this user CRS.

Supported EPSG codes are:

  • Gauss-Krueger 3 degree / DHDN: EPSG 31466-31469
  • Gauss-Krueger 3 degree / STN : EPSG 02398-02399
  • UTM / ETRS89  : EPSG 25831-25833
  • UTM / ED50  : EPSG 23031-23033
  • RD Amersfoort New  : EPSG 28992
  • Geographic ETRS89  : EPSG 4258
  • Geographic WGS84  : EPSG 4326
  • Geographic ED 50  : EPSG 4230

For the coordinate shift from DHDN/STN to ETRS89 the NTv2 method is used with the grid shift files, which are defined by NTV2GRID (DHDN) and NTV2STN (STN).

Program(s) to run before this Program

digitizer program (PC), GISMO

Program(s) to run after this Program


Additional Information



Additional software


Original Version

G. Seiß


G. Seiß



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