The StemCell 3D modeling specification is built on best practices that allow 3D models to be easily converted for multiple applications and uses. All models submitted for StemCell on TurboSquid must meet the criteria below. However, specification points that contain the RT suffix are intended for artists creating StemCell content for real-time gaming exports. Not meeting the RT criteria will disqualify a model from being converted to Unity or Unreal, but can still be converted to other DCC applications.

Note: StemCell v2 only supports a PBR Metallic/Roughness texturing workflow.

1.1 Complete model must be in a master group at the root of the scene

1.2 No rigged/procedural models or animations.

1.3 No isolated vertices

1.4 No coincident vertices

1.5 No coincident/coplanar faces

1.6 Minimal Visible Faceting – The silhouette of the model must have minimal noticeable faceting without subdivision modifiers. Most common issue for this is on round objects or sections where they intersect another surface or the background. There must be sufficient geometry for the intended silhouette of the model without drastically increasing mesh density. Relatively smaller rounded details will require less geometry to appear round when viewing the whole model. Adjust accordingly.

Example

Round legs on a table chair may only need 8 to 10 sides. Faceting would be minimally visible where the legs meet the ground or intersect with another section of the model. The thicker or larger the rounded legs, the more sides it will need to appear proportionally smooth curved.

1.7 No coincident edges (Unwelded Seams) – Any two edges on an object that meet or overlap in the same position must be welded.

1.8 No inverted face normals – No backfacing or inverted face normals. All normals should be pointing out toward the correct direction for rendering without errors.

1.9 No empty objects – All objects must be geometry or splines. Any empty objects need to be removed from the scene.

1.10 No use of smoothing groups or crease values to create hard edges – Objects should render correctly using a single smoothing group without visible faceting.

1.11 Intelligently Grouped or Combined Objects – Complex models should be intelligently combined into groups of objects. Objects must be broken up by shared material or logically by modular sections for editability. See Scene Organization and Best Practices for more detailed information.

Example

A car model can be organized with the whole body as a single object. Glass objects, such as windows, should also be combined into a separate object. The wheel, tire, and their small details combined into one object for each position on the vehicle.

1.12 Model Master Group – Entire model should be contained within a master group (group/null/locator) named the same as the model. This helps keep scenes organized when converted and merging files into new scenes. This is different than a display layer (Max) or collection (Blender).

1.13 Model on Single Non-Default Layer – Entire model should be contained within a single non-default layer named the same as the model scene. This helps keep scenes organized when converted and merging files into new scenes.

1.14 Modifiers should be applied/collapsed. The following modifiers may be left active:

“TurboSmooth”, “OpenSubDiv”, “ArnoldGeometryPropertiesModifier”, and “Subdivision Surface” (i.e. SUBSURF)

2.1 Real-world scale within 1% – Model must be in centimeter units at real-world scale. If the model does not have an exact real-world counterpart (such as a human character or an unbranded car), the model must use the size/scale of comparable objects in real life.

2.2 Exception for exceedingly large/small models – Models of objects that have a real-world scale that require magnification or distance to see, such as amoebas and solar systems, are excepted from having real-world scale.