UCS vs. DVIEW Twist

Unfortunately, in the Civil/Survey discipline, not all projects are aligned in the real world the way that we want to view them on paper. Typically, in modelspace, north is always up in the Y direction. So a road bearing N32 00’00"E will look like this:

twist1.gif (8958 bytes)

FIGURE 1

 

But when we present this on paper, we want the plot drawing to look like this:

twist2.gif (5464 bytes)

FIGURE 2

 

In order to get from figure 1 to figure 2, we somehow have to twist the drawing. There are essentially three ways that we can do this:

  1. Softdesk North Rotation - Rotate the roadway entities in the master drawing. After doing this, we can also set the Softdesk North Rotation. The purpose of setting the North Rotation is to essentially fake Softdesk into thinking that north is no longer up in the Y direction. It is now in a direction corresponding to the rotation of the roadway. Even though the roadway is rotated, north has been rotated as well to maintain accuracy.
  1. Dview Twist - Rotate the world coordinate system. In this case the roadway drawing entities are not rotated. The entire world is rotated.
  1. UCS - UCS stands for user coordinate system. By default, when you start a drawing, the user coordinate system is the same as the world coordinate system, which never changes. However, you can change the user coordinate system. Using this method, the UCS can be rotated in accordance with the road.

Also realize that twist is very important in relation to annotation. Before annotating the roadway in figure 1, the user had to know how to orient the text based on the desired twist. Choosing a method of rotation should therefore take into account the ease with which text can be oriented.

So what method should be used? Unfortunately, they are all fairly complicated. Users should have a high degree of proficiency in AutoCAD before using any of these methods. Each method has its advantages and disadvantages and they are discussed next.

Softdesk North Rotation

Advantages

a) For proper Softdesk Cogo labeling orientation and accuracy, this is the best method.

Disadvantages

a) Setting a north rotation other than the Y direction can be very dangerous if you forget that it’s set or another user does not know it’s set. All Softdesk defined alignments, dtm’s, pipes, etc. are based on the changed north rotation. Inconsistent data can therefore be created between users with different north rotations.

b) Equating initial survey information to post-design stakeout can sometimes be difficult.

c) If the user needs different orientations in different sheets or viewports, north rotation cannot help. It is only useful for one orientation.

d) The same North Rotation has to be set individually for every plan drawing in the project.

Dview Twist

Advantages

a) The accuracy and consistency of Softdesk data will not be effected. The entire world is being rotated, so the relationship between the drawing information and the coordinate system does not change.

b) Different dview twists can be set in different viewports and drawings.

Disadvantages

a) It can be difficult to correctly orient Softdesk cogo labels and AutoCAD text and dimensions.

b) It can be difficult to set the exact desired orientation.

UCS

Advantages

a) It is easy to correctly orient AutoCAD text and dimensions.

Disadvantages


a) When the UCS is set to something other than the world coodinate system (WCS), creating and defining Softdesk alignments, dtm’s, pipes, etc. will result in inaccurate and bogus Softdesk data.

b) When the UCS is set to something other than the WCS, drawings that are externally referenced will be inaccurately located.

c) When the UCS is set to something other than the WCS, lines and curves cannot be labeled accurately with Softdesk label commands.

d) One drawing can have only one UCS. It’s not possible to have different twists in different viewports using UCS.

 

Conclusion

CMI believes that Dview Twist is the best method to use. The disadvantages of using the Softdesk north rotation or UCS rotation far outweigh any advantages of UCS / north rotation and disadvantages of dview twist. Accuracy of data is most important and both UCS and north rotation can have a negative impact on accuracy.

Expert users will sometimes use a combination of dview twist and UCS. This may be okay as long as the user understands the ramifications of using UCS and always sets the UCS back to the WCS when working in Softdesk, externally referencing a drawing, or finishing a drawing. But if a user doesn’t remember to set the UCS to the WCS to do these tasks (very possible), drawing accuracy can be affected.