.. _vector.dgnv8:

Microstation DGN v8
===================

.. shortname:: DGNv8

.. build_dependencies:: Open Design Alliance Teigha library

Microstation DGN files from Microstation version 8.0 are supported for
reading and writing. Each model of the file is represented by a OGR
layer.

This driver requires to be built against the (non open source) Open
Design Alliance Teigha library.

DGN files are considered to have no georeferencing information through
OGR. Features will all have the following generic attributes:

-  Type: The integer type code as listed below in supported elements.
-  Level: The DGN level number.
-  GraphicGroup: The graphic group number.
-  ColorIndex: The color index from the dgn palette.
-  Weight: The drawing weight (thickness) for the element.
-  Style: The style value for the element.
-  ULink: User data linkage (multiple user data linkages may exist for each element).

Driver capabilities
-------------------

.. supports_create::

.. supports_georeferencing::

.. supports_virtualio::

Supported Elements
------------------

The following element types are supported in reading:

-  Cell Header (2): used for polygons with holes
-  Line (3): Line (2 points) geometry.
-  Line String (4): Multi segment line geometry.
-  Shape (6): Polygon geometry.
-  TextNode (7): Container of Text elements.
-  Curve (11): Approximated as a line geometry.
-  ComplexString (12): Treated as line string or compound curve.
-  ComplexShape (14): Treated as polygon or curve polygon.
-  Ellipse (15): Approximated as a line geometry or a circular string.
-  Arc (16): Approximated as a line geometry or a circular string.
-  Text (17): Treated as a point geometry.
-  B-Spline (21): Treated as a line geometry.
-  PointString (22): Treated as multi point.
-  Shared cell reference (35): Treated as point.

Generally speaking any concept of complex objects, and cells as
associated components is lost. Each component of a complex object or
cell is treated as a independent feature.

User data linkage
-----------------

A DGN element may have multiple user data linkages. Each linkage has
a user id, application id and a number of words of data. The user
data linkage output reports the data for each different application id.

For unknown application ids, the raw data is reported as hexadecimal
words (16bit). Is up to the user how to decode the user data, depending
on the application id.

Styling Information
-------------------

Some drawing information about features can be extracted from the
ColorIndex, Weight and Style generic attributes; however, for all
features an OGR style string has been prepared with the values encoded
in ready-to-use form for applications supporting OGR style strings.

The various kinds of linear geometries will carry style information
indicating the color, thickness and line style (i.e. dotted, solid,
etc).

Polygons (Shape elements) will carry styling information for the edge as
well as a fill color if provided. Fill patterns are not supported.

Text elements will contain the text, angle, color and size information
(expressed in ground units) in the style string.

Metadata
--------

The various metadata items that can be set in the DGN header with the
dataset creation options (see below) can be retrieved in the "DGN"
metadata domain.

Creation Issues
---------------

DGN files may be written with OGR with limitations:

-  Output features have the usual fixed DGN attributes. Attempts to
   create any other fields will fail.
-  Translation from OGR feature style strings back into DGN
   representation information is limited to a few properties of LABEL
   (text, font name, size, angle, color), PEN (color) and BRUSH (fill
   color) tools.
-  POINT geometries that are not text (Text is NULL, and the feature
   style string is not a LABEL) will be translated as a degenerate (0
   length) line element.
-  Geometries which fall outside the "design plane" of the seed file
   will be discarded, or corrupted in unpredictable ways.

Dataset creation options
------------------------

|about-dataset-creation-options|
The following dataset creation options are supported:

-  .. dsco:: SEED
      :choices: <filename>

      Specify the seed file to use.

-  .. dsco:: COPY_SEED_FILE_COLOR_TABLE
      :choices: YES, NO
      :default: NO

      Indicates whether the
      color table should be copied from the seed file. Only taken into
      account if :dsco:`SEED` is specified.

-  .. dsco:: COPY_SEED_FILE_MODEL
      :choices: YES, NO
      :default: YES

      Indicates whether the existing
      models (without their graphic contents) should be copied from the
      seed file. This holds as well for the view groups and named views to
      which they are linked to. Only taken into account if :dsco:`SEED` is
      specified.

-  .. dsco:: COPY_SEED_FILE_MODEL_CONTROL_ELEMENTS
      :choices: YES, NO
      :default: YES

      Indicates
      whether the existing control elements of models should be copied from
      the seed file. Only taken into account if :dsco:`COPY_SEED_FILE_MODEL=YES`.

-  .. dsco:: APPLICATION

      Set Application field in header. If not
      specified, derived from seed file when set. Otherwise mentions the
      version of GDAL and the Teigha library used.

-  .. dsco:: TITLE

      Set Title field in header. If not specified, from the seed file.

-  .. dsco:: SUBJECT

      Set Subject field in header. If not specified, from the seed file.

-  .. dsco:: AUTHOR

      Set Author field in header. If not specified, from the seed file.

-  .. dsco:: KEYWORDS

      Set Keywords field in header. If not specified, from the seed file.

-  .. dsco:: TEMPLATE

      Set Template field in header. If not specified, from the seed file.

-  .. dsco:: COMMENTS

      Set Comments field in header. If not specified, from the seed file.

-  .. dsco:: LAST_SAVED_BY

      Set LastSavedBy field in header. If not specified, from the seed file.

-  .. dsco:: REVISION_NUMBER

      Set RevisionNumber field in header.  If not specified, from the seed file.

-  .. dsco:: CATEGORY

      Set Category field in header. If not specified, from the seed file.

-  .. dsco:: MANAGER

      Set Manager field in header. If not specified, from the seed file.

-  .. dsco:: COMPANY

      Set Company field in header. If not specified, from the seed file.

Layer creation options
----------------------

|about-layer-creation-options|
The following layer creation options are supported:

-  .. lco:: DESCRIPTION

      Description associated with the layer. If not specified, from the seed file.

-  .. lco:: DIM
      :choices: 2, 3
      :default: 3

      Dimension (ie 2D vs 3D) of the layer. By default, 3,
      unless the model is reused from the seed file.

Building
--------

See :ref:`ODA platform support <vector.oda>` for building GDAL with ODA support.

.. toctree::
   :hidden:

   oda

--------------

-  :ref:`DGN (v7) driver <vector.dgn>`
-  :ref:`ogr_feature_style`
