# Creating Representation Item PRC Entities

The Exchange API Reference groups the PRC entities that specify individual objects present in the CAD file into the representation item module. Representation items define a particular aspect of the geometric data. The B-rep model representation item is one of the PRC entities available for packaging distinct 3D objects. Some of the other representation items include set, point set, poly B-rep model, and polywire.

- Declare a pointer to a B-rep model entity.

    A3DRiBrepModel* pBrepModel = NULL;

- Create a pointer to a populated topology B-rep data entity. (Creating Topology PRC Entities). The createTopoBrep function in the following example is a private function that returns a reference to a populated topology B-rep data entity.

    A3DTopoBrep* p = createTopoBrep();

- Declare and initialize a B-rep model data structure, and set its member values. In the following example, the m_pBrepData member references the B-rep data entity created in the previous step, and the m_bSolid member is set to FALSE, indicating that the B-rep model is a shell.

      A3DRiBrepModelData sData = A3D_MAKE_DATA(A3DRiBrepModelData);
      sData.m_pBrepData = p;
      sData.m_bSolid = FALSE;

- Package the B-rep model data as a PRC entity by invoking the A3DRiBrepModelCreate function. The first argument is a pointer to the B-rep data structure, and the second is a pointer to the B-rep model created in Step 1.

      ASInt32 iRet=A3DRiBrepModelCreate(&sData, &pBrepModel);

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