Features

STL File I/O

• Load ASCII or binary STL files from disk
• Automatic format detection (guess_format=.true.) — no need to know the file format upfront
• Load with on-the-fly clipping: clip_min / clip_max bounding box arguments discard facets outside the box during load
• Save surfaces to ASCII or binary STL

Surface Analysis

After calling surface%analize, the following data are computed and stored:

• Axis-aligned bounding box (bmin, bmax)
• Enclosed volume (volume) and centroid (centroid)
• Facet connectivity — which facets share each edge
• Disconnected-edge detection: facets with 1, 2, or 3 disconnected edges are catalogued separately
• AABB octree built automatically for acceleration

Surface Manipulation

All manipulation methods operate directly on surface_stl_object:

• Translate — by a 3D vector (delta=) or by scalar components (x=, y=, z=)
• Rotate — around an arbitrary axis by angle in radians, or by a given rotation matrix
• Mirror — with respect to a plane defined by its normal, or by a given mirror matrix
• Resize (scale) — by a 3D vector factor or by scalar per-axis factors; optionally scale about the surface centroid
• Clip — discard facets outside an axis-aligned bounding box; the cut-off remainder is returned as a separate surface
• Merge — combine two STL surfaces into one (merge_solids)
• Sanitize normals — make all facet normals consistent (outward or inward)
• Reverse normals — flip all facet normals
• Connect nearby vertices — repair disconnected edges by snapping nearby vertices together

Distance and Point-in-Polyhedra Queries

• Minimum unsigned (squared or Euclidean) distance from a point to the surface
• Signed distance (negative inside, positive outside) via:
  • Solid angle computation
  • Ray intersection counting
• Point-in-polyhedron test via solid angle or ray intersection
• compute_mesh_distance — compute distance from each node of a structured mesh block to the STL surface
• All distance queries benefit from AABB octree acceleration (up to 7× speedup over brute force)

AABB Octree Acceleration

The Axis-Aligned Bounding Box (AABB) octree is built automatically during analize. It uses 8-child (octree) subdivision and is embedded directly in surface_stl_object%aabb. The refinement depth is user-configurable and reported in statistics().

fossilizer CLI

A command-line utility (src/app/fossilizer.f90) wraps the library for interactive STL processing:

• Load one or more STL files
• Apply clip, merge, mirror, rotate, translate, resize, sanitize, and connectivity repair operations
• Print per-file statistics to stdout
• Save the result to a named output file

Compiler Support

Compiler	Status
GNU gfortran ≥ 5.3	Supported
Intel Fortran ≥ 16.x	Supported
NVIDIA HPC Fortran (nvfortran)	Supported
IBM XL Fortran	Not tested
g95	Not tested
NAG Fortran	Not tested

Design Principles

• Pure Fortran — no C extensions, no system calls beyond standard I/O
• OOP — all functionality exposed as type-bound procedures on three well-defined types
• TDD — every public operation is exercised by automated tests in src/tests/
• KISS — simple, focused API without unnecessary abstractions
• Free & Open Source — multi-licensed for both FOSS and commercial use