Spectra Precision FAST Survey Using a background map in FAST Survey - Manual (Page 5)

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5
The (x0, y0) coordinates are then:
x0 = x1 - dh and y0 = y1 + dv
x0 and y0 are the values you have to enter in the
X
Coordinate and Y Coordinate fields of the World File Editor
window.
Reading the Image Width
• Still with the graduated ruler, measure the map width.
Assuming W is the real distance in the field, then W’ is the
equivalent length measured on the map printout.
• Using Windows Explorer on your office computer, navigate
to the folder containing the image file.
• Right-click on the filename and select
Properties from the
popup menu.
• On the
Summary tab, click on the Advanced button (this
may not be necessary if the advanced parameters are
displayed by default).
• Read the number of pixels (P) displayed for the width
parameter (see example on the left).
Computing the X Resolution
• Since we have:
W / W’ = D / D’
• Then the value of the real distance W is:
W = (W’ x D) /D’
• And the X Resolution is finally equal to:
X Resolution = W /P
The X Resolution is the value you have to enter in the
X
Resolution field of the World File Editor window.
Saving the Georeferencing Information
Yo can create an ASCII text file, using a simple text editor
such as Microsoft Notepad, to save the parameters you have
just determined. The file should be saved with the tfw, jgw or
bpw extension, depending on whether the original image file
is respectively a TIF (or TIFF), JPG (or JPEG) or BMP file. The
content of the ASCII text file should always be formatted as
follows:
X Resolution (x.x)
Amount of Translation (x.xxx)
Amount of Rotation (x.xxx)
Y Resolution -x.x)