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Modeling Platystrophia

Purpose:

This article is the result of initial efforts to produce an accurate model of a Platystrophia, an extinct Brachiopod, common in the Ordovician (Platystrophia, 2011). The intent is to provide an accurate replica of several separate specimens for more accurate data collection, and as a test bed  for future projects.

Rendered Platystrophia BabyThis article will briefly go over the steps taken to go from the source image to the final model. It is worth mentioning that the first approach taken at the creation of an accurate model was through individual specimen slices. However due the the thickness of the individual slices taken from the specimen, the model accuracy, and level of detail achieved was insufficient for proper measurements to be taken. And, a great deal of surface detail was lost in the process. This article is a description of the alternate path taken in modeling of a different specimen using only a series of profile images, most specifically the image to the left.

Procedure:

The steps described were accomplished using Blender, and all original Platystrophia images were supp lied by Dr. Benjamin Dattilo, Professor Geology Indiana University–Purdue University Fort Wayne (IPFW). The reference used is the profile of a relatively young Platystrophia, and as such has several features that differ from adult specimens.

The first step in the procedure was to find a profile image that was most suitable for the creation of an outline. The image to the left was selected based on the fact that all primary features of a baby Platystrophia are clearly visible, and the changes in model elevation are sufficiently evident to be used for vertex placement. Once an image has been selected you then must scale the image as appropriate as a background in your 3D editor.

After you have scaled the image change to a view most appropriate for a flat outline of all major features, in our case the top view is most appropriate, but this may vary based on the image you choose to use as reference. Once you have completed this step your outline should look something like the image below.

After drawing the flat vertex map it is then time to adjust the height of each vertex as appropriate to achieve the desired surface features. In the case of a shell best results are achieved when a slight
rotation is applied to all lower ridge elements before translation (movement upward or downward).

Once satisfied with the outer ridge, the edges must be extruded and scaled down several times before finally terminating at a single point and then fleshing out the rest of the shell. This is the longest part of the process as it involves manually creating many polygons so that the final smoothed model actually makes sense.

Finally extrude the entire shells surface and adjust until there is no intersection between polygons, and you have achieved the desired thickness. In the case of this model there were several points that required rotation to accomplish this.

As a last step is to smooth and subdivide the surfaces until the desired model accuracy is achieved. And, when all is said and done, you should end up with something similar to the fleshed model below.

References:

Platystrophia, retrieved 12 February 2011 from http://en.wikipedia.org/wiki/Platystrophia.

The fleshed model can be downloaded in STL format by clicking the link below:

3D File Corrected For Accuracy

4 Responses to “Modeling Platystrophia”

  1. Really good document, I seriously anticipate up-dates by you.

  2. I just went through and put your feedback into action. Please let me know if there is anything else I can do to improve the accuracy of the model.

  3. Yes, better. There are a few things still not quite right, but I think it would be better to get some more views of a single specimen than to try and describe it here. Nevertheless, perhaps a bit more curvature (start closer to the origin on the spiral), only one beak, more acute angle at the beak between the interarea and the plicated outer surface (without a specimen in front of me it seems like about 45 degrees), and the presence of what is called a “sulcus” where the middle two plications . . .um . . .dip? . . .not the right word . . . .

    Here is a general discussion of the terminology used to describe brachiopod morphology:

    http://www.eps.mq.edu.au/courses/GEOS312/text/brach_morph_lecture.pdf

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