This topic documents the concepts used in creating CAD files from plan view data.
CAD Systems Supported
The system has a comprehensive CAD Output facility used to create files for use with the following CAD systems.
LISCAD CAD
AutoCAD (DXF files)
MicroStation (DGN files)
Settings and Parameter Files
The user can select which point, line and polygon objects and attributes are to be passed to the CAD file, and set the text specifications and layer for each attribute.
These selections and settings are made for each code in the data base. This enables each attribute type of each code in the data base to be individually specified giving total user flexibility over the CAD file to be created. To make maximum use of this flexibility, it is important to differentiate the objects in the data base into suitable codes before creating the CAD file.
The CAD Output settings are stored against each code in a parameter file. You can have multiple parameter files suited to producing different content CAD files. Once they are set up, you simply choose the parameter file to suit the particular type of work or particular client's needs. This facility enables CAD Output settings to be quickly established and retrieved for future use with other data bases.
Symbols and Line styles
Lookup Files to change symbol and line style names.
You may select symbol (slu) and line style (llu) lookup files, which map the LISCAD symbol and line style names, to the AutoCAD or MicroStation symbol and line style names that you wish to use.
The lookup files may be created or edited in a text editor to meet your particular name change requirements.
DXF file creation - symbol and line style geometry
You can create a DXF file for use in AutoCAD, with or without a header that defines the symbols and line styles.
If you choose to create the DXF file with a header, then the following rules apply:
When you import the DXF file into AutoCAD, ensure that you select the "No Prototype" option.
The symbols used in LISCAD will be generated as blocks in the DXF file and will have the same appearance in AutoCAD as in LISCAD.
The Line styles used in LISCAD will be generated as the appropriate AutoCAD full or dashed line style. But note that AutoCAD cannot generate any complexity in the LISCAD line style, beyond pen up pen down along the centre of the line.
If you choose to create the DXF file without a header, then the following rules apply:
When you import the DXF file into AutoCAD, ensure that you select an appropriate Prototype drawing which defines the block and line style names used in the DXF file creation.
The geometry of the AutoCAD blocks and line styles will be according to the prototype definitions.
DGN file creation - symbol and line style geometry
You can choose to use a MicroStation cell library to define the cells used in the DGN file created, and the following rules will apply.
Ensure that the cell names used in the DGN file creation are defined in the cell library.
The cells will be created in the DGN file according to the definition of the cells in the cell library specified.
Line styles are output to the DGN V7 file according to the following rules.
If the LISCAD line style name starts with, or has been renamed via a lookup file to a number between 0 and 7, then the appropriate MicroStation line style 0 to 7 is used in the DGN file.
Otherwise the line style used is the MicroStation solid line (MicroStation Line Style 0).
You should therefore always ensure that you use a line style lookup file to change the LISCAD line style names to numbers between 0 and 7, particularly if the line style names do not start with one of those numbers.
Note that there is no such restriction on line styles for DGN V8 files.
Group and Block Sensitive
The user can also control what objects are passed to the CAD file by using the system's display and block facilities. Only those objects which are on currently displayed groups and are defined by any currently active block will be output to the CAD file. The user can therefore select which groups and which region of the data base is to be output.
Note that an object or any of its attributes does not need to be displayed to be output to a CAD file. However, the group to which the object belongs must be displayed.
SEE and CAD file differences
There are some important differences between working with data in this system, and working in a CAD system using the CAD file created from in the CAD Output task.
As all of an objects attributes can have different CAD Output settings, there may be a one to many correlation between codes in this system and layers in the CAD system. This means for example that a point objects symbol, number, description, code, co-ordinates and elevation can all be passed out on different layers and where appropriate with different text specifications. This also applies for all the different line and polygon attributes.
Note however, that in the CAD file, these attributes become entities in their own right. For example, in this system, a point number has a fixed relationship with its point, but in a CAD file, the point number and the point itself can be manipulated independent of each other.
Text is displayed in the system at the same readable size no matter what the current screen viewing scale happens to be. That is, zooming in will separate the text attributes but the screen size of the text remains unchanged. This is not the same in a CAD file. Text in the CAD file is drawn at the size specified in the CAD Output settings and is displayed on the screen relative to the viewing scale. If you zoom in on a CAD file the text will appear larger.
Additional CAD data can be generated
Additional useful information may also be generated in the CAD file automatically to the user's specifications. This includes:
Co-ordinate Tables
Radiation Tables
Short Line Tables
Arc Tables
Legends
Grids
Contours
See Also
CAD Output commands