Digitize or Vectorize or Both

Over the last week I have been reviewing best practices for PDF Takeoffs with the latest version of TBC combined with the latest tools from Rockpile Solutions - and yes it does make a huge difference if you do / do not have our tools in play.

With the addition of Takeoff Lines and then Smart Join the approach to takeoff from PDF pages has changed significantly.

Let’s take a look at the issues associated with both methods

Digitizing Linework
On the face of it you would think that tracing linework would be slower than using the vector lines. The reality is that Digitizing with the Takeoff Lines command is quick and easy, and if you have a lot of straight and arc sections and elevation call outs along the lines that Digitizing is quicker for 3D Lines with variable elevations. The benefit of Digitizing is that you can also ensure that you connect lines correctly where they join or touch other lines. You also create continuous lines including arc and straight segments. You can add elevations at nodes or mid line segment etc. You can also adjust the lines with Rock Grips while drawing to get the best geometry at all times. In addition where you have lines that represent different features that occupy the same path e.g. a Building Pad and Sidewalk you can give them a little space between to ensure the surface model created has minimum errors / flags when the pad and sidewalk have different elevations.

Having said all of that, when you have contours in the PDF - these lines while they may be fragmented to varying degrees - typically with Smart Join we can join them quickly and because each line only has a single elevation we can elevate them quickly using the elevate contour functions. So in this case vectorizing linework to extract the contours is the fastest approach followed by joining with Smart Join and Elevating with Elevate Contours.

Vectorizing Linework
The vectorization process is heavily dependent on the CAD system and engineer that created the PDF - the outputs are quite variable. The challenges with vector data include

The lines are often highly fragmented and need joining
The fragmented lines are typically not touching at their endpoints - while smart join fixes these issues it is still work to create joined linework
Where two separate lines should touch eg driveways at sidewalk or ROW lines- they often don’t - they require extra work to make them touch
The lines are often duplicated so you have to clean out duplicates or overlapping portions of lines
The lines are often not broken where you want them broken - so you have to break them as needed
You still have to elevate the lines which is yet another process
Often if the PDF is not layered you end up with a mix of data on the same layer so you have to separate the linework into layers for modeling purposes.

So by the time you have cleaned up the data, joined it all together and then elevated it it would have been quicker to just digitize it. However for contours, as said previously I think it would be rare when Digitizing would be quicker than vectorizing - why is that?

Contours typically have less breaks in the line and require less joining.
Contours typically have less duplicates or overlaps or underlaps that need sorting out
Contours can be joined quickly using Smart join
Contours can be quickly elevated because they only have a single elevation

Lastly - when you have joined all of your Top Back of Curb lines, when your Flow Line or Edge of Pave line is at a offset and elevation delta to the Top Back of Curb you can use Offset Line or Sideslope (multiple Lines) to quickly create those lines from the TBC that you have created once you have that in 3D

So Best Practice

  1. Digitize your hard features with multiple elevations using the Takeoff Lines command
  2. Use Offset Line or Sideslope command to create all your offset lines (Edge of pave or flow line etc.)
  3. Vectorize the linework to extract the linework
  4. Separate existing and finished grade contours into their own layers - join them with Smart Join and then elevate them with Elevate Contour commands
  5. Use Crop Crossing command to break out the contours from hard features like Curb and Gutter , within Walls, Sidewalks etc. And crop the contours back by 0.01 at the edge of landscape areas so that the contours don’t cross or touch your elevated lines.

Follow these guidelines and you will naturally be faster at Takeoff.

Check out other posts in this series - next up is Layers and Layer Group best practices.