CONCLUSION AND DISCUSSION

This paper focused on presenting methods that could further aid in the documentation and development of online 3D databases, using PaleoView3D as a case study. The majority of online sites that specialize in 3D morphological models are designed primarily as online museums, for housing and visual comparison of models (e.g., 3D Museum, DigiMorph, MorphoBrowser, and Naturalis). Digimorph does offer downloadable 3D STL files for only 2% of its mammals, but this is obviously not the primary goal of this website. In order for the continued growth of websites that offer downloadable data, there needs to be confidence within the user-base that these data conform to their research standards. Researchers need to know the accuracy and quality of the data represented on these sites; therefore, database developers must standardize how models are produced and publish data on how models were created so that the users know potential sources and degrees of error.

Standardization of models was achieved by consistently coating specimens with ammonium chloride. Aside from noise reduction caused by reflectivity, this permitted standardization of scan parameters and laser exposure settings. New methods were also developed to expedite and semi-automate data collection. Unlike with CT model production, scanning time can often be more time intensive than image processing. Therefore, with the number (~750) and variety of specimens (dental, cranial, and post-cranial) to be included in PaleoView3D it is imperative to develop a scanning technique that could more efficiently and accurately generate 3D models of the specimens. Implementation of the mulitscan platform and macro reduced total modeling time (coating, scanning, registration, surfacing) by approximately 60% over traditional single scans. Model generation for nine isolated specimens (maximum held by platform) now takes an average of 5.5 hours (approximately 35 min per specimen) from start to finish. Using the predefined path plans, however, once a scan has been initiated, the user is free to process previously scanned data, maximizing efficiency. Because the focus of this website was not just model viewing, but producing data to be employed in morphometric analyses, it was also a requirement that these models maintain the highest degree of morphological accuracy. A multiscan platform that permitted nine specimens to be scanned (and therefore registered) at once was designed and implemented. Although this in-house model did not have the motorized rotation offered on many manufactured stages, it greatly reduced scan and registration time, at a much lower cost (~20 as opposed to ~10,000 USD), allowed for a larger work area, and was more accurate.

The image processing phase of 3D model development has the highest potential for the introduction of human error that could affect the accuracy and precision of models. Additionally, PaleoView3D is being developed at Marshall University, a primarily undergraduate institution, and the many technicians employed for the project are undergraduates with limited experience and short tenures. Therefore, another task was to make the image processing as user-friendly and automated as possible to reduce sources of error and to facilitate image processing uniformity. After specimens are registered, it is now possible to surface specimens with a single command. The autosurfacing macro that was developed includes steps that checks the manual registration process, removes noise and extreme outliers, reduces redundant points and thereby greatly reducing file size, merges the point clouds from the multiple scans, and finally "wraps" the merged point cloud into a polygonal mesh to achieve the final model. Undergraduates, in as early as their second or sophomore year, have been successfully trained to independently scan and process models.

Finally, since by necessity many of the PaleoView3D models were based on casts as opposed to original specimens, an error study was designed to compare models based on casts versus original specimens. The casting error study demonstrated, as expected, that subsequent casting generations exhibit amplified shrinkage and do vary slightly from the original specimen. In addition to the error incurred by multiple molding and casting generations, error from the scanning and modeling processes were also incorporated, making this a "worst case scenario" repeatability study. Examining the maximum range of deviation (± 0.073 mm), for the first and second generation casts, these results are considered acceptable for most morphometric analyses. The maximum variation for the third and fourth generation casts (± 0.128 mm) is certainly less desirable, but this an extreme example, and most researchers would avoid analyzing a fourth generation cast even using traditional methods. It should be noted that the goal of this study was not to show whether this modeling process was more or less accurate than any other technique, but to document the results so that the user can decide how to best utilize these data.The error studies performed on objects of known dimensions suggest that these digital models are highly accurate. The 1D study of linear accuracy resulted in a 0.4% error rate, the 2D surface area error rate was 0.05%, and the 3D or volumetric error rate was 1.79%. Manufacturers include theoretical numbers that represent the maximal possible accuracy of their instruments; however, these typically not do include a combination of potential error rate for both scanning and modeling. Analogous studies are not available to contrast how this scanner and scanning protocol compare to other systems. However, the importance is that, with this study, researchers wishing to include PaleoView3D models into their research will be aware of the error inherent in the models so they can take this into consideration when designing measurement and statistical options.

In order to gain a successful user-base and promote the sharing of data online, websites also need to be explicated concerning the sources of the data they publish. For example, associated with each PaleoView3D model is a list of technical specifications under which that model was produced including: the number of scans used to produce the model, whether a fossil or cast was scanned, what type of coating was applied to the specimen prior to scanning, the step-size or linear spacing between scans, the laser exposure time, the number of polygons that are included in the model, and the number of points that were used to derive a model. Association of these metadata with the models helps one assess the compatibility of data from multiple databases.

Due to the potential for growth of online 3D databases, we advocate the standardization of methods within sites, reporting of methodological error rates, and also explicitly documenting 3D model production protocols. By thoroughly documenting this information for PaleoView3D, we have given the user the ability to decide whether or not these data are acceptable for a particular study. We encourage all online 3D databases (present and future) to follow this approach of standardization and detailed documentation of modeling procedures, to promote the dissemination of 3D data useful for comparative analyses of paleontological specimens.