The Coordinate System icon in Sheet Space

RB 2013-06-21

WARNING: THIS IS NOT LIGHT READING!

These notes are based on testing with Windows 7 in DraftSight v1R3.1 when working in sheet space layouts.

Be aware that some of the following may only take effect after the drawing is saved and in some cases closed and re-opened so try both of those if something does not work first time.

Thinking in terms of positioning the CS (Coordinate System) icon is a mistake! That thinking makes more difficult any understanding of what is going on. I hope the following will illustrate this.

The default position of the Sheet Space CS icon is always at the WCS (World Coordinate System) origin (0,0). It cannot be moved from there. It is marked by a right angled triangle that has a small square in the right angled corner. (If the small square is not visible see “UCS” below.) However, when the user is zoomed in to sheet space so that the WCS origin is outside the drawing space a replica of the icon appears in the lower left corner of the drawing space as a reminder that work is still occurring in sheet space. That replica is NOT at the WCS origin.

Viewports and all other user-added entities, whether in a viewport or in the sheet space layout, are positioned relative to the WCS. They retain that relativity until moved to a new position by the user. The sheet (generally shown as a white rectangle) and, when visible, the PAF (Printable Area Frame – generally shown by a black, broken line, rectangular frame) move relative to the WCS origin (0,0) and icon whenever positioning changes are made to them. As a consequence they also move relative to all user-added entities.

Control of display of the PAF is achieved in TOOLS > OPTIONS > SYSTEM OPTIONS > PRINTING > GENERAL OPTIONS by checking or unchecking "Display printable area". Whether it is visible or not, the position of the PAF relative to the WCS icon remains the unchanged.

The size of the PAF may be equal to or smaller than the sheet size but cannot exceed it.

The edges of the PAF can be adjusted for position relative to the sheet edges in PRINT CONFIGURATION > PRINTER PROPERTIES -- but only for those printers that allow such settings. It seems that, when a printer has no provision for controlling the PAF margins, the PAF defaults to the edges of the sheet – that is all margins zero.

The lower left corner of the PAF defaults to the WCS origin (that is 0,0 marked by the icon).

Adjusting the margins of the PAF moves the PAF edges and the sheet relative to the WCS origin and icon without moving the lower left corner of the PAF.

Aligning a border:

Setting all the PAF margins to 0 (zero – the apparent default when no provision for adjustment is available) moves the edges of the PAF to the edges of the sheet and consequently moves the sheet so that the bottom left corner is at the WCS origin (0,0). If a pre-drawn border having its origin at the corner of the sheet is to be used as part of a sheet layout then this is the method that is recommended for aligning the corner of the sheet with the WCS origin. This should answer the often-asked question “How do I move the CS icon to the corner of the sheet?” Clearly you don't! You actually move the sheet to the icon!

Alternatively, if the origin of the border is at the lower left corner of the border then, provided provision is available to adjust PAF margins, the margins can be set to coincide with where the border is to sit on the sheet and the border will drop in place with its lower left corner precisely on the WCS origin. Note that this is NOT at the lower left corner of the sheet but at the lower left corner of the PAF. When PAF adjustment provision is not available use the former method.

It is worth noting that the former method is printer independent whereas the latter is not.

Offsetting:

Offsets affect the position of the lower left corner of the PAF in relation to the WCS origin.

Offset values appear to be interpreted as ABSOLUTE specifications; NOT RELATIVE specifications as one might expect. That is they always reference an actual x,y point on the under-lying 2D CCS (Cartesian Coordinate System) plane with reference to the WCS origin. The corresponding point on the sheet or its surrounding area is then moved to the WCS origin making it appear that the origin point has moved by that amount when, in reality, the sheet has moved in the opposite direction.

For example the WCS icon and origin (0,0) is at the lower left corner of the PAF. An x,y offset of 50,50 is applied in the Print Configuration. After the change the WCS icon appears to be at 50,50 relative to the lower left corner of the PAF making it seem that the icon has moved; But the icon is still at 0,0 (check it if you don't believe that to be so!). What has really happened is that the PAF has moved -50,-50 in relation to the CCS grid that underlies the drawing. The real movement has been in the opposite direction from that specified! Confusing? But that's the way it is! Once that is understood the effect of applying an offset is (hopefully) easier to comprehend.

Remember though that this is still an ABSOLUTE position. To reverse the offset 0,0 must be entered (NOT the intuitive -50,-50) because the lower left corner of the PAF has been moved to an absolute point on the CCS specified by the -x & -y offset pair. To reverse this simply enter, as offset values, the PREVIOUS x & y values (e.g. 0,0 > 50,50 > 0,0).

So changing the x & y Offsets in the print configuration moves both the the PAF and the sheet relative to the WCS origin (0,0) and all user-added entities. It seems that this may be intended for fine tuning the print-out position on the sheet and is likely to be of greatest use when printing directly from model space.

When printing from sheet space all user-introduced elements of a sheet space layout can be individually pre-positioned by the user within the layout and offsetting should hardly be necessary. In fact offsetting after preparing a layout will alter the relationship between all user-introduced entities in the layout and the sheet itself. For that reason it seems better to avoid offsetting when in sheet space.

Occasionally, however, the default relationship between the WCS icon and the sheet/PAF may be lost and needs to be restored. If this is just due to an applied offset, first note the offset values that have been applied and then enter 0,0 to restore the default relationship. If that does not work then restore the previous offset values to reverse the change just made because we have a problem that may require examination of the actual drawing to resolve.

In that case it may be simpler to abandon the sheet configuration that is being used and set up a new one based on the DraftSight “Standard” configuration or another configuration that is known to be good.

UCS:

If the small square is not visible in the CS icon, it is probable that a UCS (User Coordinate System) is actually in use. When that is the case, it is highly recommended that the UCS be named before doing anything else, if you want to keep it, so that its settings are not accidentally lost.

When a UCS is active the CS icon may no longer mark the position of the WCS origin and the CS icon may even be quite distant from the sheet and PAF. In that case a user can return to the WCS by selecting TOOLS > NEW CCS > WORLD from the menu system. Selecting TOOLS > NEW CCS > PREVIOUS will return to the UCS that was previously in use but this should not be relied on beyond the current session.

An active UCS does not appear to have any effect on the behaviour described in the earlier part of these notes.

An exercise:
This will demonstrate most of what has been described above.

Open a new drawing with the Standard template (FILE > NEW > STANDARD.DWT).
Confirm that “Display printable area” has a tick in the check-box in TOOLS > OPTIONS... > SYSTEM OPTIONS > PRINTING. (Tick the box if it doesn't!)
Select the “Sheet 1” tab.
Zoom to about 50%.
Delete the solid-lined rectangle that marks a viewport boundary. It's not needed for this exercise.
Draw an oblique line with its upper end at 0,0. This line is a user-added element that will serve as a fixed reference marker for 0,0 – the WCS origin.
Open the PCM (Print Configuration Manager).
Create a new “TestConfig” print configuration based on the default.
Save it.

Re-open the PCM (Print Configuration Manager) and activate “TestConfig” (Do this each time PCM is opened from here on.).
Edit “TestConfig” to

Set the DraftSight PDF printer with A3 paper (297 x 420) in Landscape orientation
Check the printer properties to make sure that it shows 30 top, and 6 for all other printable area (margin) values. Set them if it doesn't.

Save it.
The layout should now consist of the oblique line drawn previously, a white sheet representation, and a broken line PAF with the CS icon set on its lower left corner – our initial set-up.