To “Z” or not to “Z”

By Doug Aaberg • February 11th, 2018
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This one little button can have drastic effects on your company’s profitability!

 

Well ok, that might be a bit dramatic, but in reality, the decision whether or not to work in a 3D environment is something that in my early days of training I did not stress near enough. I have found that miss-using three-dimensional entities such as points, lines, and symbols is one of the most frequent cause of problems especially when it comes to creating a surface model.

Most users are very comfortable with the idea of drawing on a flat two-dimensional plane. In a sense, what you see is what you get. But in this world of surface or “model building,” learning to understand what is happening in that 3rd dimension, meaning the “Z axis” or elevation, is not only important, but in some cases essential. The problem usually occurs when a surveyor, engineer, or CAD operator are completely unaware that they are even working in a 3-dimensional environment.

Carlson has many tools in virtually all of their modules to work in a 3D environment, but as always, they offer you a choice one way or the other. The graphic shown above is contained in the Point Defaults dialog box and operates very simply. When enabled, any point you draw will be placed at the true elevation of the point. If the elevation of the point is 100, then it will be placed in the drawing with a “Z” value of 100. All of that seems simple enough but somehow, sometimes, drawings still end up looking like this:

Before I go any further on this topic, I must state clearly that I am NOT trying to deter anyone from working in a 3D environment. My purpose in this blog is to point out the differences, pros and cons, and potential pitfalls, and then offer some solutions for both past and future projects when dealing with 3D entities.

2D or 3D, what is the difference?

When drawing in a 2D environment, your points will be placed at elevation 0 and your lines, polylines and arcs will be created at a single elevation, which is usually also 0. That is not to say that a 2D polyline cannot be created at an elevation. Contour lines for example are 2D polylines drawn at the elevation of the contour. Every vertex along that polyline will have the same elevation. By default, when creating a surface model, Carlson will use any entity drawn at an elevation other than 0. (That is exactly 0 out to many decimal places so you need not worry about performing topographic surveys at sea level.)

When drawing in a 3D environment, your points will be placed at the elevation indicated and 3D polylines can have different elevations for each vertex. Symbols and text also have the option of being placed at a true elevation, usually the same as the point they are associated with.

Pros and Cons

When assisting a company in setting up their working environment, I have witnessed what can only be considered arguments over whether or not to work in 2D or 3D. The answer usually lies in your individual work flow and what CAD platform you may be used to.

Those users who have migrated to Carlson from LDT are used to drafting 2D entities and are completely unaware that Carlson offers a 3D choice. If they want to draw a line, they simply select the icon for [Line] or type “L” at command line then “snap” to a node and away they go. The problem occurs when that node is at an elevation; the beginning point of the line now has a “Z” value. If they draw to a second point by distance, screen picking or by snapping to a point with a different “Z” value, they have now created a sloped line instead of a horizontal one. Then when using other commands like perpendicular snap, list entity, or Triangulate and contour, the results are not what were intended and could be very inaccurate. A similar issue occurs when drawing a polyline except that the entire polyline is drawn at the beginning elevation.

The great benefit to working in 3D is the exactly flipside to that just mentioned. If you want to begin a line or polyline at a known elevation, you just simply snap to a “node” and begin drawing. In the case of a 3D polyline, you can start at an elevation by snapping “nearest” without the effort of manually interpolating between two points.

Pitfalls

The pitfalls of making elevation errors become self-evident once you realize that you are working in that environment. If a user draws a line with one end point at an elevation of 100 and the second at 0, they have introduced a 100 foot “spike” in their surface model. Since Carlson will use any entity with a “Z” value, it will attempt to contour to that spike creating a hole or mound that does not exist.

Likewise, if a user were to draw a polyline for something like a building footprint starting at an elevation, they would create a flat spot in the surface. Many times a user who is not utilizing the Field to Finish program, (which is another discussion to have), places a single symbol such as a tree and then copies it around the rest of the drawing. The issue occurs when the first symbol was placed at an elevation, again snapping to a “node.” The rest of the trees then either have that same elevation or, in some instances, a relative elevation between two points used when copying. The result is inaccurate elevations placed throughout the drawing. The same issue often occurs with text.

Solutions

When beginning a drawing, Carlson offers specific tools to work within either a 2D or 3D environment.

1. In the draw menu, you will find both 2D and 3D lines as well as 2D and 3D polyline options.

 

The 2D options will force a line or polyline to be drawn at elevation 0 regardless of the beginning point elevation. This is a great option for those working with 3D entities to ensure accidental “spikes” or erroneous elevations will not be introduced into the drawing.

Similarly, the 3D options allow those working in a 2D world to easily create 3D entities when desired. Remembering that Carlson only needs 3D polylines for breaklines, that is often the only time a user need worry about it.

2. The Edit menu also contains tools to work with 3D and 2D objects. Things like offsetting or filleting a 3D polyline that are usually difficult and problematic are easily handled.

 

3. In both the Point Defaults and Field to Finish Code Table editor, you have options to set the controls for the placement of points on a Real “Z” or not.

 

It is advisable that these settings be the same one way or the other to avoid confusion.

1. Use Point snaps instead of Nodes

In the Draft menu, Carlson offers a specific Point snap that reads directly to a Carlson point only. When drawing a 3D polyline, this filter will aid in extracting the correct point elevation.

If you discover that a completed project has these kinds of vertical errors, Carlson also offers some fixes.

1. Analyze the data: From the View pulldown menu select Viewpoint 3D and set the XY Plane to 0

 

 

2. Drawing Cleanup. From the File pulldown menu select Drawing Cleanup.

 

There are a myriad of choices to automate the cleanup and error fix process. By selecting Scan Drawing, the program will display the lowest and highest elevations in the drawing. If you review your point elevations in the coordinate file, determine the correct elevation range, you can select the Set Elevations Outside Range to Zero option, type in the correct range and allow Carlson to do the rest.

3. Flatten objects. From the Edit pull-down menu, select 3D Entity to 2D

 

This command allows you to manually select entities, including points, and set them to elevation 0. A great benefit of this command is that it will modify endpoints of a line or polyline to be zero while maintaining its horizontal geometry.

Conclusions

I would be totally remiss if I did not point out the fact that Carlson’s Field to Finish program will allow you to create 2D and 3D objects directly from the field collected data eliminating most of the need to draw lines and polylines, to begin with. Reducing these kinds of errors is enough incentive to start using Field to Finish in and of itself. If you want help getting that started, download my Easy Start Guide here.

I hesitate to offer an opinion on whether or not to work in a 2D or 3D environment because I myself tend to use both. What I do advise is that a discussion take place within your firm and a decision be made. It is then imperative that every employee recognize and understand the environment they are working in to eliminate these kinds of errors that can be both costly and liable.

For more instructions and great conversations, consider coming to this year’s User’s Conference and attend some classes.

FYI, San Diego is warm http://www.carlsonsw.com/community/user-conference/

Doug

Let’s Grow Together.

Douglas L. Aaberg, PLS
Survey Product Manager
P)617-393-2300×419
daaberg@carlsonsw.com

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