Planet Four Talk

A Method For Measuring Objects In The Images.

  • Kitharode by Kitharode moderator

    Although the method outlined below will not give precise measurements it will provide a fair degree of accuracy for larger objects seen in the images. The smaller the object the more uncertain the results will be, but good 'ball park' figures can still be achieved.

    The Planet Four images are 840 x 648 pixels. One pixel = 49.6 cm

    Therefore 840 x 49.6cm = 41,664cm = 416.64m.
    Likewise, 648 x 49.6cm = 32,141cm = 321.14m.

    If you visit an image from your collection and 'right click' on it, then click 'view image', the image should fill most of your screen. On my screen, this produces an image that is 20cm x 17cm. It'll probably be different on your screen, but the procedure is the same.

    We now know that the P4 image (in round figures) is 416m across. My onscreen image is 20cm across. So 416m divided by 20cm gives me 20.8m/cm (2.08m/mm) across my onscreen image.

    Therefore if I measure a blotch or boulder at, say, 1.5mm, then 2.08 x 1.5 = 3.12. The measured object is ~3.12m across.


  • angi60 by angi60 in response to Kitharode's comment.

    Excellent stuff Kitharode. Judging the size of objects was something which alluded me, so this is very useful. Well done 😃


  • andreagonzalez by andreagonzalez

    We are doing a report for Astrophysics about Planet 4 project and I found this information about measuring objects in the images really helpful. How did you manage to get the pixels of the images? By the way the method is really clear 😃


  • Kitharode by Kitharode moderator in response to andreagonzalez's comment.

    Hi there. I'm really pleased to hear that you found the method helpful. I got the pixel data from the P4 scientists. The science team here are very helpful, so if you have any questions that we (the volunteers) can't answer then one of the scientists will jump in and answer it for us.

    Is your report for 'Astrophysics' the magazine, or something else? I'd be interested in seeing it. Cheers, Kitharode.


  • p.titchin by p.titchin

    great easy solution Wassock. On my screen, it works out to the third decimal point as the same as the Ibs to kilos conversion (2.2046) and as my mind has got used to doing a quick conversion on that over the last 25 years it refines my 'gut' approximations I have been doing on the 'football pitch' approximations'. Thanks again. ~Pete


  • pete-j by pete-j

    This topic has been discussed and posted and similar links are:

    Scaling factors and The scale of them photos.

    I noted an apparent contradiction when one of the images has apparently dual-binning (i.e. two possible scales in one image) to which P4 Scientist Anya replied (see links above).