**System Information**
Windows 8.1 x64
Renderer: GeForce GTX 860M/PCIe/SSE2
**Blender Version**
Broken: 2.74.5 05c4c24
**Short description of error**
Decimate modifier generates concave edges with certain geometry while in Planar mode.
**Exact steps for others to reproduce the error**
# Open blend file {F177716}
# Enable Decimate modifier:
## on the most left object (hard edges) → no concave edges
## on the center object (smooth edges) → concave edges, very nasty
## on the most right object (more smooth edges) → concave edges, but no intersections (so technically model is fine)
Use case for this is jewelry design, it's better to optimize your models before boolean operations, and it is always appreciated to keep your STL file size small as possible to send them by email.
Here is simple GIF animation to illustrate the issue:
{F177719}
Note: I cannot use Collapse mode, because it generates artifacts that are impossible to fix.
{F177722}