> For the complete documentation index, see [llms.txt](https://c3dlabs.gitbook.io/c3dlabs-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://c3dlabs.gitbook.io/c3dlabs-docs/developing-cad-applications-with-a-geometry-kernel.md). # Developing CAD Applications With a Geometry Kernel Building a CAD application means separating domain-specific behavior from the mathematics required to construct and modify geometry. The application may manage commands, feature history, assemblies, constraints, visualization and user interaction, while a dedicated geometry engine performs operations on curves, surfaces and solid bodies. This separation allows engineering software teams to concentrate on application logic without implementing every low-level modeling algorithm themselves. ### Defining the Boundary Between Application and Kernel A [geometric modeling kernel](https://c3dlabs.com/products/c3d-toolkit/modeler/) typically provides data structures and algorithms for representing geometry and topology. The application communicates with these capabilities through an API or SDK. The division of responsibilities should be explicit. The kernel can create an extrusion, calculate an intersection or perform a Boolean operation, but the application normally determines why that operation is required and what it means within the engineering workflow. For example, a mechanical CAD application may represent a hole as a parametric feature containing diameter, depth and placement information. At the modeling level, creating that feature may involve constructing cylindrical geometry and subtracting a tool body from another solid. The kernel processes the geometry; the application preserves the semantic meaning of the feature. ### Building Models Through the API Most CAD application development begins with relatively simple geometric entities. A sketch may contain lines, arcs and spline curves. Closed profiles can then drive operations such as extrusion or revolution. More complex construction may use sweeps, lofts and surface operations before producing a closed solid. Once solids exist, the application can invoke Boolean union, intersection and subtraction, as well as filleting, chamfering, shelling and other geometric operations. The resulting 3D models are commonly represented using B-Rep topology. Faces reference underlying surfaces, edges correspond to curves, and vertices define positions. The application may need to traverse these structures to select geometry, calculate properties or associate kernel entities with higher-level objects. ### Handling Operations That Do Not Succeed Kernel operations should not be treated as commands that always return valid geometry. Consider a fillet request. A selected radius may be too large for the surrounding geometry, neighboring faces may create difficult intersections, or the operation may generate regions that cannot form valid topology. Boolean operations have similar failure cases when bodies contain problematic geometry or near-coincident surfaces. Application code should therefore inspect operation results rather than assume success. Depending on the workflow, it may need to preserve the previous model state, report a meaningful error, adjust parameters or attempt an alternative construction strategy. This makes error handling a fundamental part of integrating a geometric kernel, not an auxiliary concern. ### Tolerances and Imported Geometry Numerical tolerance also affects application architecture. CAD calculations use finite-precision arithmetic, so entities that are intended to coincide may differ by small numerical amounts. These differences become particularly visible when engineering software works with imported geometry. Adjacent surfaces may contain gaps, edges may not align perfectly, and topology may require validation or repair before additional modeling operations can be performed reliably. Developers should understand the tolerance rules exposed by the kernel and avoid introducing arbitrary comparisons of floating-point coordinates at the application level. Model validity should be evaluated using the same geometric concepts that govern kernel operations. ### Managing Topological Change One of the harder integration problems is maintaining references to model entities after geometry changes. Suppose an application stores a reference to a particular face. A later Boolean operation or fillet may split that face into several new faces, replace it or remove it completely. The application's original reference may no longer describe the intended region. This affects feature histories, dimensions, constraints, annotations and selection persistence. Applications that depend heavily on persistent model references therefore need a deliberate strategy for tracking topology across edits rather than relying only on transient face or edge identifiers. ### Designing the Application Around Modeling Semantics A geometry kernel provides computational capabilities, but it does not define the complete architecture of a CAD, CAM, CAE or BIM system. The application still needs its own model of engineering intent: features, assemblies, dependencies, constraints, manufacturing information or domain-specific objects. Kernel entities should support these concepts rather than replace them. The most maintainable architecture keeps this distinction clear. Low-level geometry remains responsible for mathematical and topological consistency, while higher application layers manage engineering semantics and workflows. When those responsibilities are separated carefully, complex 3D modeling operations can be integrated without forcing domain logic into the geometry engine itself. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. 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