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Screen Protractor

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For WindowsScreen Protractor

Work with engineering plans or designs to measure degrees or radians on your screen.

Posted in the Screen Protractor Forum.




How does it account for the aspect ratio ?

How does the tool account for the aspect ratio of the screen or image being measured ? I can't find anywhere where it calibrates itself by measuring the same distance in the vertical and horizontal dimension.

If I measure an angle on a picture in a Word document for example, and then stretch the image horizontally or vertically (Unclick Lock Aspect ratio), and measure the angle again, I get a different answer. But the angle hasn't really changed - only the image has.

No image or screen is guaranteed to have a 1:1 aspect ratio. So without the ability to measure vertical and horizontal distance as part of calibration, I can't see how you can measure angles accurately, as this requires taking account of the aspect ratio.
by Tim on Nov 3 2009 2:53am Reply

How does it account for the aspect ratio ?

Tim,

If you stretch an image horizontally or vertically in Word or Photoshop then the angle is going to change, the protractor can't really account for that.

The Protractor's measurement is based off of the pixels sent to the screen, not the screen itself, so if the screen's aspect ratio is slightly wide then the protractor will account for that.h
by Nico Westerdale on Nov 3 2009 10:28am Reply

How does it account for the aspect ratio ?

My "stretching the image" example was only to explain the effect of a non 1:1 aspect ratio.

But when measuring angles you can't assume that any image or anything on a computer screen has a 1:1 aspect ratio. If I am measuring an angle on an digital xray for example, I have to know that magnification is the same in both dimensions, or is incorporated into the calibration of the measuring tool.

It sounds like your tool takes the screen aspect ratio into account by working in pixels rather than physical size on the screen, but that's only half the issue. You would need to incorporate a measurement of a known horizontal and vertical distance into your calibration process in order to get accurate angles.
by Tim on Nov 3 2009 9:22pm Reply

How does it account for the aspect ratio ?

Thanks for the clarification, but I think you're over-thinking the problem. If the image itself was taken with the correct aspect ratio it does not matter if you screen is stretched in any direction as both the image and the protrator would be stretched by exactly the same amount.

Imagine you hook up a projector to your computer and shine the image head on on a wall, the aspect ratio would be correct and you would use the protractor correctly. If you then angled the projector so that it was at an angle to the wall then the protractor wiould still measure the angle on the image correctly, even though it would be distorted.

Does that answer your question?
by Nico Westerdale on Nov 3 2009 9:31pm Reply

How does it account for the aspect ratio ?

In the world of scientific measurement I inhabit, images do not necessarily have the same vertical and horizontal scale. So we need to calibrate both dimensions before measuring distances or angles.

"Imagine you hook up a projector to your computer and shine the image head on on a wall, the aspect ratio would be correct and you would use the protractor correctly. "

The measured angles would only be correct if the image being projected has a 1:1 aspect ratio. If for example the image shows 1 metre as 10% longer in the vertical than the horizontal dimension, then any angle measured from that image (other than 90, 180, 240, 360 degs) will be incorrect.
by Tim on Nov 4 2009 11:08pm Reply

How does it account for the aspect ratio ?

Tim,

Thanks for explaining further, I see your need however it's not a very common request (the first I've ever heard). I think a solution for you would be to manipulate the image to correct the aspect ratio and then measure it with the protractor.
by Nico Westerdale on Nov 5 2009 11:15am Reply

How does it account for the aspect ratio ?

I think a solution for you would be to manipulate the image to correct the aspect ratio

But that's the problem - one doesn't know for sure what the aspect ratio is in any image without a means of measuring the same known distance in an image, in both the horizontal and vertical dimensions.

Most scientific measurement software that I've used has had that feature.

So while you haven't heard it asked for before, that's because most people assume all their images have the correct aspect ratio ... but they don't ! :-)
by on Nov 13 2009 12:08am Reply

How does it account for the aspect ratio ?

You could always use our Screen Calieprs to measure your image exactly!
by Nico Westerdale on Nov 13 2009 3:44am Reply

How does it account for the aspect ratio ?

Hi Tim,

I have just downloaded Screen Protractor and am disappointed. I intend to use it for the sole purpose of measuring angles on clinical radiographs. I fully understand your query and I agree that this software is not appropriate for accurate measurements.

Have you come across any other software that is useful for measuring radiographic angles?

Many thanks,
JOHN
by John McGuire on Apr 27 2010 5:58pm Reply

How does it account for the aspect ratio ?

John,

I think you are misinterpreting how the software works. The Screen Protractor is one of the most accurate ways of measuring anything on a computer screen. If the aspect ratio of your screen is changed then the Screen Protractor will of course change with it. I assume that in 99% of circumstances this is what you would want to happen - you want the angles measured as they would be in the original image and not on an incorrectly stretched image on a monitor that is set to be too wide or narrow.
by Nico Westerdale on Apr 28 2010 12:39am Reply

How does it account for the aspect ratio ?

Hi,
I agree that this tool needs to be able to account for screen aspect ratio.  I use it to calculate decline on graphs for oil and gas production data.  It would be idea to be able to add a slope output for the custom units.  Also to get the actual slope of a graph on the screen, it is necessary to adjust for the rectangle of the plot area and normalize it to the screen aspect ratio.  I have an excel file which I use to account for this but it requires some extra steps.

Is possible to include what I am hoping to do?  At the least, a slope unit would be great and the ability to put formulas into the calibrate units section.

Please let me know if you need any screen grabs to describe what I am referring to.

Thanks,
Craig
by Craig Sorensen on Oct 21 2010 6:35pm Reply

How does it account for the aspect ratio ?

Hi Craig,

Thanks for the improvement ideas. I have written them down.

It would help if you could send over any screen grabs to see exactly what you mean. You can send them to florea@iconico.com

Also please notice that I don't know for sure an exact date for when these improvements will be included into the application.

Thanks!
Constantin
by Constantin Florea on Oct 22 2010 5:19am Reply

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