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In our mollusk type imaging project, images from which are viewable at <a href="http://clade.ansp.org/malacology/collections/search.php?search=advanced" id="LPNoLP339223">
http://clade.ansp.org/malacology/collections/search.php?search=advanced</a>, we include a scale bar laid on the center line of the specimen in the vertical plane where that is practicable. For things under a certain size, or where the specimen has enough depth
to require image stacking, however, we record the maximum measured dimension as a number on the image itself.
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Scale bars on images are largely there to indicate relative size, not for users to take accurate measurements from. Nowadays it's easy to include maximum-diameter measurements in image metadata or an associated database.</div>
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<div style="font-family:Tahoma; font-size:13px"><b>Paul Callomon</b><br>
<i>Collection Manager, Malacology and General Invertebrates</i><br>
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<font face="Verdana"><b>Academy of Natural Sciences of Drexel University, Philadelphia</b></font><br>
<i>callomon@ansp.org Tel 215-405-5096 - Fax 215-299-1170</i><br>
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<div id="divRplyFwdMsg" dir="ltr"><font style="font-size:11pt" face="Calibri, sans-serif" color="#000000"><b>From:</b> Nhcoll-l <nhcoll-l-bounces@mailman.yale.edu> on behalf of Gary W Shugart <gshugart@pugetsound.edu><br>
<b>Sent:</b> Friday, June 5, 2020 1:02 PM<br>
<b>To:</b> nhcoll-l@mailman.yale.edu <nhcoll-l@mailman.yale.edu><br>
<b>Subject:</b> [Nhcoll-l] 3D scales in 2D images</font>
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Hi All: When I take a picture of a specimen I usually include a scale ruler on the stage or at the base. It didn't occur to me until recently that the scale will not apply for any part of the object not on the same plane as the base. The differences are substantial
with eggs, nests, bones. For example using a scale on a base plane compared to two scales above separated by pencils (7 mm) and the top scale is 10 mm = 11 mm at base (reference photo on Slater Museum FB page (https://tinyurl.com/ybnjkq2r). Searching Google
and this appears to be something like perspective or forced perspective (not parallax view) . There are explanations of angular size calculation online and calculators, but you have to know the distance between the base and plane to calculate a size. I noticed
this especially in the new Birds of the World (formerly Birds of North American) account with eggs and nest with a scale. Also recall the issue occurred in egg photographs.
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<div>How to deal with this? This depends on the purpose of the scale. If to just give a general idea of size it doesn't matter. But if the idea is to use the scale to set the scale in imagej or other measuring software, it is a problem. A pain to set up
and redo for each object though. Or actually deal with specimens and measure them IRL.<br>
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<div>Gary Shugart<br>
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<div>Collection Manager<br>
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<div>Slater Museum<br>
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<div>Tacoma, WA <br>
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