World file (*.jgw, etc.)¶
World file gives coordinate data to an image to overlap an image with a grid. The following is an example of a world file. Words in parentheses ( ) are remarks and are not included in the actual file.
2.5 (a: increment of x-coordinate per pixel)
0.0 (b: rotation condition)
0.0 (c: rotation condition)
-2.5 (d: increment of y-coordinate per pixel)
-131.82 (e: x-coordinate of the pixel at top left of the image)
223.57 (f: y-coordinate of the pixel at top left of the image)
“a” expresses an increment of x-coordinate per 1 pixel movement from left to right. “d” expresses an increment of y-coordinate per 1 pixel movement from top to bottom.
Coordinates (e, f) express the coordinates of the pixel of top left image.
“b” and “c” express rotation. However, iRIC does not read “b” and “c” because it does not accommodate “rotation.”
Table 45 shows the relationship between an image file and the extension of georeferenced file.
| Image file | Georeferenced file |
|---|---|
| *.jpg, *.jpeg | *.jgw |
| *.png | *.pgw |
| *.bmp | *.bpw |
| *.tif | *.tfw |
When a world file that has the same base name with image file exists in the same directory, the world file is read for and used to adjust the alignment of the image data.