Coordinate Systems

The coordinate systems determine the parameters which the application uses to process drawing data. The coordinate system determines whether you wish to work in a cartesian, isometric or dimetric system. By entering an angle of rotation the orientation of the coordinate system can be displayed. In addition, you can specify measurement units for lengths and angles as well as the type on number, floating point decimals and fractions. The scale is saved with the coordinate system and the position and display grids can be set here. You can set the coordinate system parameters via a dialog called with the command Manage > Coordinate Systems > Edit.

Each drawing can have several coordinate systems defined within it. This can be useful if you have several drawing windows and wish to use a different coordinate system with each one, perform dimensions in a different coordinate system to that you are drawing in, or use objects with different scales in the same drawing.

To change the current coordinate system apply the corresponding button in the Ruler or select the command Manage > Coordinate System > Edit.

Scales and Units

The most important components of a coordinate system are the scale and the units. The scale determines the "real" size of an object, i.e. how large a drawn object is supposed to be in the model world. Using a scale of 1:20 means that an object whose length is 10 cm on the paper is supposed to have a length of 200 cm in reality.

Above all, scales are influencing dimensions, i.e. dimension objects within a drawing. Dimension do always show the "real" size of an object based on the scale, and not its size on the paper. This is why each dimension is directly linked to a coordinate system, out if which is determines the scaling information. In addition, it uses the desired length and angle units stored in the coordinate system for the dimension.

If dimensions are to be linked to a specific coordinate system, this can either be done in advance by means of the Annotate > Dimension Parameters command, or afterwards by means of the Modify > Object Properties > Edit command.

Anyway, the scale and the units do not only influence dimensions placed in the drawing, but all types of measurement, both during user entry (e.g. numerical input of a length) and during screen output (e.g. the coordinate display in the Status Window).

If you do not like the default measurement units of a coordinate system during input, you can choose different ones (e.g. cm instead of mm) by typing the abbreviation for that unit after the figure. You can use this procedure in all dialogs. You can combine different units in the same calculation (see Extra > Coordinate Input (F8)).

Grids

Another important component of coordinate systems are grids, which are divided into position grid and display grid.

The position grid is an invisible, regular series of points which the crosshairs move along. The points are always the same distance in one direction from another. The horizontal and vertical divisions can be different. The crosshairs 'snap' from point to point. This ensures that you can only move the crosshairs in multiples of the specified grid interval.

The display grid shows the grid as small dots on the screen. It can be set separately from the position grid. You can choose a larger display grid than position grid. This speeds up screen redraws considerably and makes for a better overview as not so many points obstruct your view of the objects. If the zoom level is too small, that is if the display grid is too small and the number of points to be shown too large, the display grid is first automatically enlarged and then turned off. As soon as you revert to a level at which the grid can be displayed, it is turned on again.

Both grids are valid for the currently active coordinate system and can be defined as part of it.

The first point of each grid is at the origin. In order to be able to work with a common starting point for the grid in different windows using different coordinate systems, the origin should be moved so that all the grids can be used effectively. To do this, choose the command Manage > Coordinate Systems > Set Origin.