[Back to Blog](/blog) # External Parameter Definitions in Teigha BIM

Alexander Geniatov October 19, 2017 [\#rvt](/blog/tag/rvt) [\#rfa](/blog/tag/rfa) [\#getting started](/blog/tag/getting-started)

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Teigha BIM supports external parameter definitions, which are entities stored in external text files and not included in project/family documents but can be imported into documents. Parameter elements of the ParamElemExternal class store the guid of an external parameter definition.

#### External parameter definitions file structure

Here is a simple example of how these files look:

```
*META	VERSION	MINVERSION
META	2	1
*GROUP	ID	NAME
GROUP	1	1
GROUP	2	2
GROUP	3	Exported Parameters
*PARAM	GUID	NAME	DATATYPE	DATACATEGORY	GROUP	VISIBLE	DESCRIPTION	USERMODIFIABLE
PARAM	f5ff6402-9260-4e5a-9f8e-49d14a351e19	Area	AREA		3	1		1
PARAM	1f8f5e6f-f6e9-43a0-a059-d610dfd26402	Param11	TEXT		2	1	Desc1	1
PARAM	844695f1-a33f-40d7-aacf-a0e131d51a97	Param 2	FORCE		1	1	444	1

```

- The META section corresponds to metadata, version 2 with minversion 2 files that are used in all modern versions of .rvt/.rfa files. Currently it’s the only version supported in Teigha BIM.
- The Groups section represents groups of external parameter definitions; each group has a name and ID (both fields are unique). These groups have no relation to parameter groups or anything else in .rvt/.rfa documents and are used only for grouping external parameter definitions (for example, in the Shared parameters dialog).
- The Params section contains external parameter definitions.

Each section begins with a header string starting with the “\*” symbol and contains a list of fields in a section table. The fields in both headers and entity tables are separated with tab symbols.

#### External parameter definitions in Teigha BIM

All interfaces required for working with external parameter files are located in the Database/BmExtParamDef.h file. The file defines two classes:

- OdBmExtParamDef — Represents external parameter definitions.
- OdBmExtParamDefFile — Represents a file for storing external parameters and groups.

#### OdBmExtParamDef class

This class represents an external parameter definition, and its fields correspond to fields of entities in the PARAM section:

- OdString m\_name; — Name of parameter that goes to the caption field of OdBmParamDef.
- OdBm::ParameterType m\_dataType; — Parameter type that defines which child of OdBmParamDef will be used and the unitType for ParamDefValue.
- OdInt64 m\_dataCategory; — Defines the family type category (applicable for family type parameters only).
- OdUInt32 m\_groupId; — ID of the group that the parameter belongs to.
- bool m\_isVisible; — Visibility flag that corresponds to the IsUserVisible field of OdBmParamDef.
- OdString m\_description; — Description that goes to the description field of ParamElemExternal.

In addition to get and set methods, the class contains a method for creating a parameter definition that can be used for creation of database parameters (ParamElemExternal), i.e. to import an external definition to the database; the class also contains a constructor for creating an external definition with OdBmParamDef that exports parameters from the database to shared parameter files.

```
OdBmParamDefPtr getParamDef(const OdBmDatabasePtr& pDb) const;
OdBmExtParamDef(const OdBmParamDefPtr& pParamDef, OdUInt32 groupId, const OdString& description);

```

#### OdBmExtParamDefFile class

This class represents a database (file) of external parameter definitions and provides an interface for loading and saving the database from/to a stream and adding, removing, etc. parameter definitions and groups.

- getGroups — Returns a group’s id-string name map as a constant ref.
- addGroup — Adds a group. If a negative ID is passed, the interface allocates an ID itself and returns it.
- deleteGroup — Deletes a group. A group can be deleted only if it doesn’t contain parameter definitions.
- renameGroup — Renames a group.
- isValidGroup — Validates whether a group with the passed ID is present in the database.
- getParams — Returns the parameter definitions guid-OdBmExtParamDef map as a constant ref.
- getParamsByGroup — Returns the map of the parameter definitions belonging to a group.
- getParamByGUID — Returns the parameter definition by guid.
- addParam — Adds a parameter definition to the database. Returns the error id with the param name if the guid is not unique or the datatype or group are invalid.
- deleteParam — Deletes a parameter.
- moveParam — Moves a parameter to another group.
- getParamTypeByTag — Returns the ParameterType by string tag used in the DATACATEGORY field of the PARAM section records in the file (for example, the tag AREA corresponds to parameter type OdBm:: kPT\_Area).
- getParamTypeTag — ReturnsParameterType by string tag DATACATEGORY.
- loadFromStream — Loads database content from the stream.
- saveToStream — Saves database content to the stream.

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