[Nhcoll-l] 3D scales in 2D images

[Adam Rountrey]

Perhaps, a telecentric lens could be used?
-Adam







On Fri, Jun 5, 2020 at 1:36 PM Callomon,Paul <prc44 at drexel.edu> wrote:

> In our mollusk type imaging project, images from which are viewable at
> http://clade.ansp.org/malacology/collections/search.php?search=advanced,
> 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.
> 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.
>
>
>
> *Paul Callomon*
> *Collection Manager, Malacology and General Invertebrates*
> ------------------------------
> *Academy of Natural Sciences of Drexel University, Philadelphia*
> *callomon at ansp.org <callomon at ansp.org> Tel 215-405-5096 - Fax 215-299-1170*
>
>
> ------------------------------
> *From:* Nhcoll-l <nhcoll-l-bounces at mailman.yale.edu> on behalf of Gary W
> Shugart <gshugart at pugetsound.edu>
> *Sent:* Friday, June 5, 2020 1:02 PM
> *To:* nhcoll-l at mailman.yale.edu <nhcoll-l at mailman.yale.edu>
> *Subject:* [Nhcoll-l] 3D scales in 2D images
>
>
> External.
>
> 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.
>
> 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.
>
> Gary Shugart
> Collection Manager
> Slater Museum
> Tacoma, WA
>
>
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