DXF (Data Exchange Format) is a widely used standard for transferring graphical data between computer-aided design and drafting (CAD) systems such as AutoCAD. Many architects and surveyors use CAD for the production of building plans, site layouts and survey drawings. Ordnance Survey also supplies many of its products in DXF format.
DXF files may be included as overlays using the Create New Overlay wizard in the usual way. If the graphics in the DXF file have been positioned using the National Grid coordinate system, and the unit of measurement used is the metre, DXF data appears in the correct geographical position.
Architects and engineers who have produced the data without regard to its location in the world may have selected a convenient local position as the origin of the coordinate system for the data. In this case SIS provides the ability to move it to its correct geographical position, rotating it as necessary, and defining the units of measurement used.
To display a DXF file which is not correctly geo-referenced, it is important that you know the geographical location of at least one point on the DXF graphics. For instance, if you were using the National Grid coordinate system projection, you must establish the National Grid reference of a point on the DXF graphics. You may need to consult the provider of the DXF file to obtain this information.
Example
The following example uses a DXF file which is to be positioned within the National Grid.
Scale
Enlarge or reduce the items on the cursor by the specified value. This value is relative to its current size, and ignores any previous enlargement or reduction.
Mirror
Check the tickbox to create a mirror image of the graphics on the cursor, using the specified angle as the mirror plane. 0 degrees is horizontal, 45 degrees is bottom-left to top-right, and 90 degrees is vertical.
Rotate about Axes
X/Y - Define three-dimensional rotation about the X/Y axes. These options are only useful in 3D modelling.
Z - Rotate the items on the cursor through the specified angle. Positive angles are anti-clockwise, negative angles are clockwise.
On completion click OK.
The details of this transformation are saved in the file, so that when you next load this SWD file (using Open [Application]) the DXF dataset will be in the correct location.
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