software to measure length on screen
 

I need to extract y-data from a graph in pdf file. Thinking of using
the mouse to click the end points to return me the distance. Is there a software for this?

Hi...

You didn't mention which distribution and version of Linux you're using but you can try ScreenRuler. It might be available in your distribution's repositories. :)

Regards...

Found screenruler on web. But I tried to yum install on Centos 6.6 but there seems none. :( Thanks.

Hi...

It might be found in another repository. Which ones do you have enabled?

Also, I found a "tarball" of this program here, although you may need some Ruby and/or Glade files to meet any dependency requirements, although I'm not sure what CentOS 6.6 has available and/or will the program will need precisely. You may need to use an older version of ScreenRuler depending on the version of Ruby. :)

Regards...

the old carpenters auto retracting measuring tape is just not enough now days. :(

it'd need to computate scale length to actual length

Yes...BUT you would also need to factor in:

• The size of the graph ITSELF
• How much that graph is scaled on the PDF as an image (the graph may have started out as 1280x1024, but be on the page as 320x200)
• How much the PDF itself is scaled/zoomed when measurement is taken

..which would be near impossible to know, unless you were the author of the PDF/Graph to start with (are you, OP??) Your original post said you needed to extract the y-data...what do you mean here, since you follow it up with your need to know how long the line is? Distance on a graph line will tell you very little, since one inch (let's say) on a graph measuring a months worth of data, and one inch on a graph measuring a YEARS worth are still "one inch", but the data represented is going to be vastly different.

More information needed on your end goal and data sets, please.

that's why we need to know actually what is on the display, which program was used to draw what, was it 2d or 3d or something else, and what kind of distance is required (in pixel, in meter or in ???). Pdf probably includes an embedded image, but probably not....?

yep
pixels converted into inches depending on size of screen display to get distance from point a to point b. then you'd take that and put it to what the scale of the graff is and well it is quite difficult to say the lease. unless you're a math head.