how to convert pixels into measurement-html5 canvas

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if my canvas is reflecting some real life measurements like 8 meter by 6 meter and i draw a line on it, how can i calculate the measurement of that line on canvas. i.e if i draw from position x1,y1 to position x2,y2 i measure it and say for sure that it is approximately x length long. Also will it be possible to show the measurement right below the line on runtime too like as soon as i finish the line,its length is automatically be shown at bottom of it. i am using simple canvas with just 1 draw line function with javascript atm.

Posted 8-Mar-14 8:54am

mughees ilyas

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Kornfeld Eliyahu Peter · Answer 1 · 2014-03-08T09:26:00

Solution 1

To convert pixels to real time measurements you first need to know the DPI of your the monitor, means how many dots it have in inch - that's why it called DPI...
Unfortunately for you there is no way to get this info from OS using JavaScript...

Posted 8-Mar-14 9:26am

Kornfeld Eliyahu Peter

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mughees ilyas 8-Mar-14 15:37pm

well lets just say that my screen is 75 dpi and most screens usually are 75 dpi
and my canvas is 300 by 300
what next

Kornfeld Eliyahu Peter 8-Mar-14 15:51pm

I checked all my monitors (there are 3) and all have 120 DPI...
However if you have 300 dots (pixels) it is 4 inches on a 75 DPI monitor, that's about 9.8 cm...

mughees ilyas 8-Mar-14 18:28pm

m pretty sure monitors have ppi not dpi actually ._.
anyway ur ans is not helpful atall

Kornfeld Eliyahu Peter 9-Mar-14 0:44am

PPI = Pixel Per Inch
DPI = Dot Per Inch
I'm not a native English but pretty sure dot and pixel can used (at least here) as same...
Maybe my answer isn't useful because you try to do something that can't be done... :-)