I am trying to convert a ZTL file to an OBJ file. I first load the STL file using Zplugin -> ZBrush 3D Print HUB -> Import STL File and then Zplugin -> ZBrush 3D Print HUB -> Export to OBJ. The resulting OBJ file, though preserves the polygonal geometry information like v, vt or f, does not contains normals, i.e., the vn field. The version of ZBrush I am using is ZBrush 2018 (but the same issue exists in 4R8). The STL model is downloaded from https://www.turbosquid.com/3d-models/mountain-rock-pbr-8k-3d-model-1300107. Since I am not familiar with the ZTL file format spec, could any friend here please help me check whether the original STL file does not contain normal information at all, or I missed some option during the conversion in ZBrush. Thanks a lot!
ZBrush doesn’t use normals so they are probably discarded on import.
You can export an OBJ with smoothed normals by using the Export button at the top of the Tool palette. Make sure you turn on Smooth Normals in the Tool>Export sub-palette first.
The rock model I want contains sharp angles and corners as opposed to cobbles or boulders. The smoothed normals may destroy the geometry desired. So, are you sure that the normals are discarded when the ZTL file is being loaded? Is there any way to check the existence of normal information in the ZTL file? Or is there other tools available that can preserve normals during conversion? Thanks a lot.
The normal information in a 3D file is simply instruction to the render engine of how light should be reflected from the object. Most rendering applications will give you the option of switching between smooth and hard normals, and generating the normals if they don’t exist. Normals do not change the geometry of the mesh but are calculated from it.
The rock model you downloaded is high resolution and so the difference between the effect of smoothed normals and hard normals is likely to be very slight and probably not noticeable (the polygons are so small). Depending on what you are wanting to do I’d leave out the smoothed normals.
ZTL (that is ZBrush Tool) files do not include normals.
STL files - used often for 3D printing and imported into ZBrush through the 3DPrint Hub plugin - do include hard normals but they are not relevant for 3D printing.
Thank you very much, Marcus.