Lecture Notes

Return to ARC550 home page

• Database structure
• dblist
• list

• Graphic element

• All modeling programs, both 2-D and 3-D have databases
• Some tasks alter the database, while others do not.
• Relational databases can have thousands of tables all linked together.
• As a side note: one of the toughest things that a computer must do is to take the 3-D information contained on the database, and project it on a 2-D surface (the screen).
• History of the concept of layers.
• Information that was going to be repetitive (would appear on more than on drawing), would be drawing on mylar sheets.
• To compose a desired drawing, the necessary mylar sheets, or layers, would be laid on top of one and another, being aligned by five, quarter inch pegs, which corresponded to five holes in each of the layers.
• These sheets are then taken to the local reproduction house to be photographed by large cameras.
• So this idea of layers has been taken to AutoCAD, and is an example of some of the data stored on the AutoCAD database.
• One graphic element occupies only one row of the database.
• Usually the first field (the intersection of a row and a column in called a field) contains the ID tag. This is a unique name that the application assigns to each graphic element.
• Other examples of data stored in the database can be color, line type, space, object type.
• Note: if we are talking about a single point, it depends on the mentality of programmer, because a single point has no dimensions, therefore it cannot have a color or a line type.
• Locations or points are stored in units, not architectural dimensions for example.
• The program translates the data into whatever unit the user wants to deal with.
• Both AutoCAD and Form· Z use double precision math.
• This rounds every value calculated in the programs to the 64^th decimal point.
• To access the database on AutoCAD, type dblist. This will bring up the much of the database. If one just wishes to view on object, type list, and then click on the desired object.