Go to: SmartForest Home Printer-friendly: sf-impl.pdf

The .elev File

Parsing the .elev file begins in the function named read_DEMFile. read_DEMFile first calls elevReader where the actual reading of the file occurs. After the file is read by elevReader, control returns to read_DEMFile. read_DEMFile continues by setting some global (yuck) variables based on the data read from the .elev file.

The elevReader function utilizes the scanner provided in tokenizer.c. It creates an encapsulated variable called elev. elev's contents are accessible using the accessor functions provided in elevReader.c. The first six values comprise the header of the .elev file. elev is formatted as follows:

Never	Data	Field	Purpose
Used	Type	Name
	int	nCols	The number of columns in the DEM file.
	int	nRows	The number of rows in the DEM file.
	int	xllCorner	The x-component of the south-west corner.
	int	yllCorner	The y-component of the south-west corner.
	int	cellSize	The width and height of each grid. The value is often 30. (Meters)
	int	noDataVal	The value used to represent ``No Data''
	float[][]	elevInfo	The elevation information. Each datum represents the height
			of the sample. The units are not specified but are likely feet.
			The data is read from the file in row-major order.

Once elev is initialized, its values are used to initialize the global variables that are actually used by the application. In this light, elev may be viewed solely as an interface to the contents of the file while the global variables are the data abstractions used by the application. The variables are as follows:

Global Variable Name (Application Abstraction)	Initialized by elev Field (File Interface)
columnCount	nCols
rowCount	nRows
x_sw	xllCorner
y_sw	yllCorner
x_ave	cellSize * nRows
y_ave	cellSize * nCols
map $[col][nRows - row - 1][0]$	0
map $[col][nRows - row - 1][1]$	0
map $[col][nRows - row - 1][2]$	elevInfo$[col][row]$

Notice that the initialization of map reverses the order of the rows in elevInfo.