Pitney Bowes MapInfo Vertical Mapper - Manual (Page 73)

Chapter 5: Creating Grids Using Other Methods
User Guide
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the projection, z-unit type, and a number used as a special flag indicating null value grid cells. The
default null value is -9999.0; however, if the data includes -9999.0 as a valid numeric value, a new
null can be assigned to grid cells with no value.
Example of a grid file illustrating the construction of an ASCII grid file.
ASCII Classified Grid is a simple text-based format consisting of general grid information in the file
header followed by rows of space-delimited integer values. The header of the file contains a lookup
table of class values, which define the integer representing each class name. The value 0 is used to
define the null cell (a cell that is not defined in the lookup table). The lookup table should always
begin sequentially with the value 1. The maximum number of classes included in this format is
65 535.
Example of a simple classified import file.
CRC-500 is a binary DEM for RF propagation modeling supported by Canada’s Communications
Research Centre. The grid cell resolution is 500 metres in a UTM projection using the NAD 27
datum for Canada.
DTED is a binary DEM originally supported by the U.S. Defence Mapping Agency (now NIMA). The
Grid Import utility recognizes both Level 1 (3 arc-second) and Level 2 (1 arc-second) in the
latitude/longitude coordinate system.
Geological Survey of Canada Grid is a text-based, delimited format grid file supported by the
Survey for a number of geophysical data themes at a variety of grid cell resolutions and projections.