CAD Cross Section Conversion Process

In this video I show the same process as for Vector PDF data, however this time I am working with CAD Sections in the Plan View. This data has its own types of issue - again boiling down to my standard approach for all sections allows me to get these processed pretty much first time.

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I am trying to learn more about using this method. Can you take a little more time to explain (illustrate) how to properly scale the cross sections for the CAD and PDF examples?


Brian Sarvis

Let’s start with CAD files which are typically “more accurate” than PDF files.

Depending on the cross section type (no grid, single or multiple) we will have different amounts of scale information to work with.

No grid means that we only have a datum elevation and a zero offset line and we have to provide the scale for the horizontal and vertical. Typically one section file will be constant throughout the whole data set and you have to find the scale data - sometimes it will be drawn somewhere in the drawings other times you need to find two elevations (datum plus a call out) and measure the vertical distance (Y axis distance) to see what TBC sees eg 10’ and then see what the callous tell you eg 5’ and then you know the vertical is exaggerated 2:1 so we would scale by .5 to squash the vertical back to 1:1. Normally CAD sections have a horizontal scale of 1:1 unless they were plotted at half scale and again you need to measure an X distance and compare with a known distance like a pavement width to check it. Then we scale 1:1 in the convert process.

When we have a Single Grid - each section typically has a vertical grid for offsets and those are labeled and a horizontal grid for elevation and those are labeled so the converter looks at the grid line spacing and the labels to determine the scales automatically.

When we have the multiple sections in a grid then similar to the single option we have the x and y grids and the text labels and we use those to derive the scales.

With PDF if you have lines and text then the processes are basically the same but from the sheet view, with the following differences

  1. in sheet view the pdf pages are typically scaled like a drawing eg 50 scale which is 1:600 so we woukd have to scale them by 600 to get them to 1:1, and the vertical exaggeration may be 1 or 2 etc and 2 at 50 scale then we have to scale by 300 to get to 1:1. All that can be derived from the grids and labels in the single or multiple sections and for no grid you need to derive it from what is in the sections or drawings etc - often the title box will have the scales or they will have it somewhere on the sheets or there is something you can measure to check it.

Problem with PDF is that often you do not get Text - only polyline equivalents of text which you cannot Use for scale. So in that case we recommend converting the sections to the no grid method (keep one grid line for elevation and one for 0 offset and then elevate the elev grid lines with the datum elevation and elevate the offset grid lines with 0 elevation for a 0 offset, and then determine the scales manually and apply them in the converter.

I hope this answers the question - if not let me know and I will post a video explaining it better on Monday