Transferring of pixels into mm

[firelex]

Hello, all!
My problem is:
I have a canvas and am trying to transfer pixel coordinates into mm. The point is: with the growing
number of pixels it gets rather complicated to figure out the exact number of mm from pixels.
The formula I use is
[tt]<number of pixels> / <number of pixel in mm>[/tt]

Is there any exacter one?

Thanks.

 

[ulis]

To get the pixels count from a mm count, see winfo pixels or winfo fpixels.
See:

http://www.purl.org/tcl/home/man/tcl8.4/TkCmd/winfo.html

To give mm lengthes in place of pixels lengthes you append m to the length (20m == 20 mm). See Tk_getPixels for more details.
From the Tk manual:
These procedures take as argument a specification of distance on the screen (objPtr or string) and compute the corresponding distance either in integer pixels or floating-point millimeters. In either case, objPtr or string specifies a screen distance as a floating-point number followed by one of the following characters that indicates units:

<none>
The number specifies a distance in pixels.
c
The number specifies a distance in centimeters on the screen.
i
The number specifies a distance in inches on the screen.
m
The number specifies a distance in millimeters on the screen.
p
The number specifies a distance in printer's points (1/72 inch) on the screen.

HTH

ulis