Geometry & modeling
Parasolid
Definition
Parasolid is Siemens' geometric modeling kernel and XT file format for exact B-Rep solids, surfaces, and related model data. When two CAD applications both use Parasolid, an XT handoff can reduce the translation boundaries between them, but it still does not preserve the source application's feature history.
Also known as: Parasolid XT, XT, .x_t, .x_b
Updated
A kernel and a file format#
Parasolid is the geometric engine inside many CAD, CAM, and CAE products. It supplies operations for solid modeling, direct editing, surfaces, facets, and geometry queries. Siemens also publishes the Parasolid XT format so applications can exchange the kernel's model data.
Siemens says the XT format is shared by more than 350 applications from more than 200 software vendors. Those are vendor-reported adoption figures, not an independent compatibility test.
Why an XT file can be useful#
An XT transfer between applications that both use Parasolid can avoid converting geometry into a separate neutral representation and back. Onshape's supported-format table calls Parasolid B-Rep its preferred import format and lists support for text .x_t and binary .x_b files.
That shared kernel does not preserve everything from the authoring system. Features, sketches, constraints, mates, configurations, and drawings are application-level data. A Parasolid export usually preserves the finished bodies and surfaces, not the decisions that built them.
Parasolid compared with STEP#
Parasolid XT is a proprietary kernel format. STEP is an ISO family of neutral product-data standards. XT is often the direct choice when both applications use Parasolid; STEP is the safer general request when the receiver or its kernel is unknown.
Whichever one you use, validate units, body count, geometry, assembly placement, and any required metadata in the receiving system before releasing the model.
Sources
Related terms
B-Rep
B-Rep is the way professional CAD kernels describe a solid: by its boundary, made of exact surfaces (faces), the curves where they meet (edges), and the points where edges end (vertices). Because the geometry is exact and the topology is explicit, B-Rep models can be measured, filleted, dimensioned, and manufactured precisely.
CAD kernel
A CAD kernel is the geometry engine inside a CAD program that creates and modifies solids: booleans, fillets, shells, intersections, and tessellation for display. Parasolid and Open CASCADE are common examples, and the kernel largely decides which operations are reliable and how exports behave.
CAD translation
CAD translation converts geometry and product data from one CAD system or file format into another. It can preserve exact solids while losing feature history, names, colors, assembly structure, or PMI, depending on the source format and the receiving translator.
STEP
STEP is the ISO 10303 family of standards for exchanging 3D product data between CAD systems, usually saved as .step or .stp files. A STEP file carries exact B-Rep solid geometry that another CAD program can measure and edit, but it normally does not carry the original feature history.