栅格坐标信息文件 TFW或JGW的解释 Joe

How georeferencing information is accessed

The image-to-world transformation is accessed each time an image is displayed, for example, when you pan or zoom. The transformation is calculated from one of the following sources, listed in order of priority:

• The header file (if the image type supports one)
  
• The world file (This will be used first if the Use world file to define the coordinates of the raster check box is checked on the Options dialog box.)
  
• From the row/column information of the image (an identity transformation)
  

World file contents

The contents of the world file will look similar to this:

	20.17541308822119 	0.00000000000000 	0.00000000000000 	-20.17541308822119 	424178.11472601280548 	4313415.90726399607956

When this file is present, ArcView performs the image-to-world transformation. The image-to-world transformation is a six-parameter affine transformation in the form of

	x1 = Ax + By + C 	

        y1 = Dx + Ey + F

where

	x1 = calculated x-coordinate of the pixel on the map 	

	y1 =  calculated y-coordinate of the pixel on the map 	

	x = column number of a pixel in the image 	

	y = row number of a pixel in the image 	

	A = x-scale; dimension of a pixel in map units in x direction 	

	B, D = rotation terms 

	C, F = translation terms; x,y map coordinates of the center of the upper left pixel 	

	E = negative of y-scale; dimension of a pixel in map units in y direction

NOTE: The y-scale (E) is negative because the origins of an image and a geographic coordinate system are different. The origin of an image is located in the upper left corner, whereas the origin of the map coordinate system is located in the lower left corner. Row values in the image increase from the origin downward, while y-coordinate values in the map increase from the origin upward.

The transformation parameters are stored in the world file in this order:

	20.17541308822119 - A   	

	0.00000000000000 - D 	

	0.00000000000000 - B 	

	-20.17541308822119 - E 	

	424178.11472601280548 - C 	

	4313415.90726399607956 - F