7.7 lattice.for

Be aware that LATTICESPOT does interpolate between adjacent cells if the points are not exactly located in the center of the sampled cell. There is a free AML to download from ESRI's hompage that enables to sample grids into a point file without interpolations. The AML is called GRIDSPOT (or GRIDSPT7, respectively).

When the program is started, the following qustion are asked:

• Enter value (m) for X-min (lower left):
• Enter value (m) for Y-min (lower left):
• Enter value (m) for X-Increment:
• Enter value (m) for Y-Increment:
• Enter number of (vertical) columns:
• Enter number of (horizontal) rows:

The program creates a file called <coord.dat>, which contains the newly gnerated coordinates. This file can be imported into ArcInfo easily using the generate command in the ARC-module:

   arc:\>generate new_ptfile
   arc:\>input coord.dat
   arc:\>points
   arc:\>quit
   arc:\>build new_ptfile points

When designing a lattice to the extent of an existing grid, you should know that the describe command in ARC (or GRID) gives you all the information necessary to answer the above questions. Be aware however, that the reported lower left coordinates are the absolute lower left of the grid cell (edge), not of the center of this cell. To get the center of the lower left cell, you should add half of the cell size to both the X- and the Y-coordinate. Also, there might be NODATA cells at the edges of the grid. If tis happens, then you would generate a lattice that covers the whole grid, but one that covers a larger area than the one containing actual data values.

The last thing you should be aware is that files can become very large if e.g. a few thousand rows and columns are entered each. If you need to sample an overly large area, it might be a better idea to split the whole study area into pieces and sample them sequentially. The lattice program facilitates this approach.

General specifications of the AML:

References:

 

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