README.md

ForCAD: A parallel Fortran library for geometric modeling using NURBS (Non-Uniform Rational B-Splines).

ForCAD supports B-Spline, NURBS, Bezier and Rational Bezier curves, surfaces and volumes.

Table of Contents

• Table of Contents
• Main Features
• Examples
• Installation
  • Requirements
  • Clone the repository
  • Install PyVista (Optional)
  • Using fpm
    • Running Examples with fpm
    • Using ForCAD as a fpm Dependency
  • Using CMake
    • Install
    • Uninstall
    • Using ForCAD with CMake
• Configuration
  • Do Concurrent Support
  • Precision Configuration
• Dependencies
• CI Status
• API documentation
• Contributing
• Citation
• References

Main Features

• Parallelized using do concurrent.
• Create NURBS objects by specifying control points, weights and knots.
• Refine NURBS objects by inserting or removing knots and elevating degree.
• Compute analytical basis functions and their first and second derivatives for NURBS and B-Spline objects.
• Generation of IGA-compatible element connectivity and shape functions.
• Obtain visualized elements connectivity and coordinates for geometry and control geometry.
• Mesh insertion into a NURBS object.
• Export NURBS objects to VTK files for visualization.
• Export of NURBS curves and surfaces to IGES format (volumes currently not supported).
• Includes predefined NURBS shapes: Circle, Half Circle, Tetragon, Hexahedron, 2D Ring, Half 2D Ring, 3D Ring, Half 3D Ring, C-shapes.
• Rotate and translate NURBS objects.
• Visualization using provided python PyVista scripts.
• Least squares fitting for NURBS curves, surfaces and volumes.
• Numerical integration of: NURBS curve length, NURBS surface area and NURBS volume.

Examples

Below are some sample outputs from the examples directory:

Installation

Requirements

• Fortran compiler:

  • GNU Fortran (gfortran)
  • Intel Fortran Compiler (ifx)
  • NVIDIA HPC SDK Fortran Compiler (nvfortran)
  • LLVM Flang (flang)

  Note: Latest compiler versions are required to ensure compatibility.

• Build system:

  • Fortran Package Manager (fpm)
  • CMake

• Optional visualization tools:

  • PyVista (recommended)
  • ParaView

Clone the repository

Clone the ForCAD repository from GitHub:

git clone https://github.com/gha3mi/forcad.git
cd forcad

Install PyVista (Optional)

To install PyVista, run the following command:

pip install pyvista

By default PyVista visualization is enabled. To disable it, define the preprocessor flag NOSHOW_PYVISTA in the fpm.toml file or pass it as a compiler flag.

Using fpm

Running Examples with fpm

fpm run --example <file name excluding the .f90 extension> --compiler gfortran --profile release --flag "-ftree-parallelize-loops=8 -march=native"

After executing the examples, .vtk files will be generated in the vtk directory. To visualize these files, a show() method is provided which utilizes PyVista. Alternatively, other visualization tools like ParaView can also be used.

Using ForCAD as a fpm Dependency

If you want to use ForCAD as a dependency in your own fpm project, you can easily include it by adding the following line to your fpm.toml file:

[dependencies]
forcad = {git="https://github.com/gha3mi/forcad.git"}

Using CMake

Install

cmake -S . -B build/cmake -DCMAKE_BUILD_TYPE=Release -DBUILD_SHARED_LIBS=ON -DCMAKE_INSTALL_PREFIX=. -G Ninja
cmake --build build/cmake --config Release
cmake --install build/cmake --config Release --verbose

Uninstall

cmake --build build/cmake --target uninstall

Using ForCAD with CMake

find_package(forcad REQUIRED)
add_executable(app main.f90)
target_link_libraries(app PRIVATE forcad::forcad)

Configuration

Do Concurrent Support

Compiler flags for enabling do concurrent parallelism:

Compiler	Flag(s)
gfortran	-fopenmp -ftree-parallelize-loops=n
ifx	-qopenmp -fopenmp-target-do-concurrent
nvfortran	-stdpar=multicore,gpu -Minfo=stdpar,accel
flang(-new)	-fopenmp -fdo-concurrent-to-openmp=[host|device]
lfortran	?

flang-new 21.1.0: warning: Mapping do concurrent to OpenMP is still experimental.

Compiler flags can be passed to fpm using the --flag option, for example:

fpm build --flag "-stdpar=multicore,gpu -Minfo=stdpar,accel"

Alternatively, flags can be added to a fpm.rsp file in the root directory of the project.

Precision Configuration

The library uses double precision (real64) by default for all real-valued computations. To change the precision, you can define one of the following preprocessor flags during compilation:

Preprocessor Flag	Fortran Kind	Description
REAL32	selected_real_kind(6)	Single precision
REAL64 (default)	selected_real_kind(15)	Double precision
REALXDP	selected_real_kind(18)	Extended double precision
REAL128	selected_real_kind(33)	Quadruple precision

Note: The examples example_ppm1.f90, example_ppm2.f90 and example_ppm3.f90 use the ForColormap library, which only supports REAL64 precision.

Example: Building with double precision

fpm build --profile release --flag "-DREAL64"

Dependencies

flowchart LR
  N1[forcad]
  N2[forIGES]
  N3[fordebug]
  N4[forunittest]
  N5[forimage]
  N6[forcolormap]
  N7[fortime]
  N8[FACE]

  click N1 href "https://github.com/gha3mi/forcad" "A parallel Fortran library for geometric modeling using NURBS"
  click N2 href "https://github.com/rweed/forIGES" "Modern Fortran Library for Reading and Writing IGES CAD Files"
  click N3 href "https://github.com/gha3mi/fordebug" "A Fortran library for handling errors, warnings and info messages with debugging support in pure procedures"
  click N4 href "https://github.com/gha3mi/forunittest" "A Fortran library for unit testing"
  click N5 href "https://github.com/gha3mi/forimage" "A Fortran library for processing and editing images and managing colors"
  click N6 href "https://github.com/vmagnin/forcolormap" "A Fortran colormap library"
  click N7 href "https://github.com/gha3mi/fortime" "A Fortran library for measuring elapsed time, DATE_AND_TIME time, CPU time, OMP time and MPI time"
  click N8 href "https://github.com/szaghi/FACE" "Fortran Ansi Colors (and Styles) Environment"

  %% core dependencies
  N1 --> N2
  N1 --> N3
  N3 --> N7
  N7 --> N8

  %% example dependency (dashed line)
  N1 -.->|example| N6
  N6 --> N5

  %% test dependency (dotted line)
  N1 ...->|test| N4
  N4 --> N8

Graph generated with fpm-deps, modified to include example and test dependencies.

CI Status

OS	Compiler	Version	fpm	cmake
ubuntu 24.04	flang-new	22.1.5	0.13.0 ✅	4.3.3 ✅
ubuntu 24.04	gfortran	15.2.0	0.13.0 ✅	4.3.3 ✅
ubuntu 24.04	ifx	2026.0.0	0.13.0 ✅	4.3.3 ✅
ubuntu 24.04	nvfortran	26.3	0.13.0 ✅	4.3.3 ✅
macos 15	gfortran	15.2.0	0.13.0 ✅	4.3.3 ✅
windows 2025	gfortran	15.2.0	0.13.0 ✅	4.3.3 ✅
windows 2025	ifx	2026.0.0	0.12.0 ✅	4.3.3 ✅

This table is automatically generated by the CI workflow using setup-fortran-conda.

API documentation

The most up-to-date API documentation for the master branch is available here. To generate the API documentation for ForCAD using ford run the following command:

ford README.md

Contributing

To contribute to ForCAD, please review the CONTRIBUTING.md.

Citation

If you use ForCAD in your research, please cite it as follows:

@software{seyed_ali_ghasemi_2025_10904447,
  author       = {Ghasemi, S. A.},
  title        = {gha3mi/ForCAD},
  year         = {2025},
  publisher    = {Zenodo},
  doi          = {10.5281/zenodo.10904447},
  url          = {https://doi.org/10.5281/zenodo.10904447}
}

References

• Piegl, L., & Tiller, W. (1995). The NURBS Book. In Monographs in Visual Communications. Springer Berlin Heidelberg. https://doi.org/10.1007/978-3-642-97385-7

• An Introduction to NURBS. (2001). Elsevier. https://doi.org/10.1016/b978-1-55860-669-2.x5000-3

• Sullivan et al., (2019). PyVista: 3D plotting and mesh analysis through a streamlined interface for the Visualization Toolkit (VTK). Journal of Open Source Software, 4(37), 1450, https://doi.org/10.21105/joss.01450

• Ahrens, James, Geveci, Berk, Law, Charles, ParaView: An End-User Tool for Large Data Visualization, Visualization Handbook, Elsevier, 2005, ISBN-13: 9780123875822