MicroStation Levels for MDL Developers

Q What the user sees and what the MDL (or VBA) developer knows are different things. The difference can lead to confusion and prompt question similar to these …

• Where is the Level ID?
• What is a Level code?
• What is the field Number in MicroStation's level dialogs?
• I see a level number in MDL, but why is it different to the number in the Level Manager dialog?

A There are three pieces of information about a level: its name, code, and number. The user (or CAD Administrator) assigns the level name and level code. MicroStation assigns internally a number — the Level ID — to each level; the ID is not exposed to the user.

• Level IDs, level codes, and level names are unique within a DGN file. Each model in that DGN will see a consistent set of names, IDs, and codes
• The corollary of the above is that although Level IDs are unique within a DGN file, that is not true of levels in different DGN files. MicroStation may assign a different Level ID to a named level in one DGN file compared to another DGN file.
• Each level in a DGN has a unique internal ID, which is the value returned by mdlElement_getProperties(). The internal ID is not exposed to the user: you will only ever see it as a VBA or MDL developer The internal ID of a given level name is consistent within a DGN file, but is likely to be different in another DGN file
• Level names are user-assigned. The internal level ID is assigned automatically by MicroStation
• Level codes are user-assigned. They are the numbers you see in the user interface. A level code is simply an alias for the user name. It is not related to the internal level ID. Obtain a level code from a level ID with mdlLevel_getCode()

As an MDL or VBA developer, we work with level IDs, and must be aware that the level ID of a given name in one file is probably different to the level ID of that level name in another file. For example, if you are working with reference files, the ID of level 'Named MicroStation may assign a different Level ID to a named level in one DGN file compared to another DGN file. Level' in the active model is going to be different to the level ID of 'Named Level' in an attached model stored in a different DGN.

Q What about Levels 1…63 from MicroStation/J?

A The Level ID is assigned internally by MicroStation, and you can't control it. You can assign level codes 1…63. However, if you convert a V7 file to V8 you will find that those level numbers are created automatically by MicroStation.