EVOLUTION-MANAGER

Edit File: drv_dgn.html

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<head>
<title>Microstation DGN</title>
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<h1>Microstation DGN</h1>

Microstation DGN files from Microstation versions predating version 8.0
are supported for reading (a <a href="drv_dgnv8.html">DGNv8 driver</a>,
using Teigha libraries, is available to read and write DGN v8 files).
The entire file is represented as one layer
(named "elements").

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

<ul>
<li> Type: The integer type code as listed below in supported elements.
<li> Level: The DGN level number (0-63).
<li> GraphicGroup: The graphic group number.
<li> ColorIndex: The color index from the dgn palette.
<li> Weight: The drawing weight (thickness) for the element.
<li> Style: The style value for the element.
</ul>

DGN files do not contain spatial indexes; however, the DGN driver does take
advantage of the extents information at the beginning of each element to
minimize processing of elements outside the current spatial filter window
when in effect.

<h2>Supported Elements</h2>

The following element types are supported:

<ul>
<li> Line (3): Line geometry.
<li> Line String (4): Multi segment line geometry.
<li> Shape (6): Polygon geometry.
<li> Curve (11): Approximated as a line geometry.
<li> B-Spline (21): Treated (inaccurately) as a line geometry.
<li> Arc (16): Approximated as a line geometry.
<li> Ellipse (15): Approximated as a line geometry.
<li> Text (17): Treated as a point geometry.
</ul>

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.

<h2>Styling Information</h2>

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.

<h2>Creation Issues</h2>

2D DGN files may be written with OGR with significant limitations:

<ul>
<li> Output features have the usual fixed DGN attributes. Attempts to create
any other fields will fail.

<li> Virtual no effort is currently made to translate OGR feature style
strings back into DGN representation information.

<li> 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.

<li> Polygon, and multipolygon objects will be translated to simple polygons
with all rings other than the first discarded.

<li> Polygons and line strings with too many vertices will be split into
a group of elements prefixed with a Complex Shape Header or Complex Chain
Header element as appropriate.

<li> A seed file must be provided (or if not provided,
$PREFIX/share/gdal/seed_2d.dgn will be used). Many aspects of the resulting
DGN file are determined by the seed file, and cannot be affected via OGR,
such as initial view window.

<li> The various collection geometries other than MultiPolygon are completely
discarded at this time.

<li> Geometries which fall outside the "design plane" of the seed file will
be discarded, or corrupted in unpredictable ways.

<li> DGN files can only have one layer. Attempts
to create more than one layer in a DGN file will fail.

</ul>

The dataset creation supports the following options:

<ul>

<li> 3D=YES or NO: Determine whether 2D (seed_2d.dgn)
or 3D (seed_3d.dgn) seed file should be used. This option is ignored if the
SEED option is provided.

<li> SEED=filename: Override the seed file to use.

<li> COPY_WHOLE_SEED_FILE=YES/NO: Indicate whether the whole
seed file should be copied. If not, only the first three elements (and
potentially the color table) will be copied. Default is NO.

<li> COPY_SEED_FILE_COLOR_TABLE=YES/NO: Indicates whether the
color table should be copied from the seed file. By default this is NO.

<li> MASTER_UNIT_NAME=name: Override the master unit name from
the seed file with the provided one or two character unit name.

<li> SUB_UNIT_NAME=name: Override the sub unit name from
the seed file with the provided one or two character unit name.

<li> SUB_UNITS_PER_MASTER_UNIT=count: Override the number of
subunits per master unit. By default the seed file value is used.

<li> UOR_PER_SUB_UNIT=count: Override the number of
UORs (Units of Resolution) per sub unit. By default the seed file value is
used.

<li> ORIGIN=x,y,z: Override the origin of the design plane. By
default the origin from the seed file is used.

</ul>

<hr>

<ul>
<li> <a href="http://dgnlib.maptools.org/">Dgnlib Page</a>
<li> <a href="http://gdal.org/ogr_feature_style.html">OGR Feature Style Specification</a>
<li> <a href="drv_dgnv8.html">DGNv8 driver</a> (using Teigha libraries)
</ul>

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