With the introduction of CAD, virtually every transaction or operation in the AEC Industry needs a CAD file. Operations ranging from sale, certification, addition and alteration need a CAD file so as do activities like valuation, project management, and of late, even maintenance (Through Intelligent Building Management Systems). While CAD is all of 2 decades old, buildings that undergo these transactions are much, much, much older, with drawings available on paper, sometimes on ancient blueprints.

This Blog looks at the process involved in Architectural PDF to CAD conversion.

Input

Accuracy in Architectural PDF to CAD conversion depends heavily on the type and quality of input, which could be in any of these forms:

  • Blueprint of manually drafted drawing
  • Scan of  CAD Print
  • PDF output from CAD file

Information

In addition to the actual drawing input, certain information is necessary for the Convertor, such as:

  • Scale of input drawing (if not mentioned)
  • If scale is not known, then 5 to 10 important measurements in X and Y axes must be given. Best would be to give grid dimensions, or something similar, like room sizes, or floor heights.
  • Material specifications and pictures – in case of illegible scans or damaged blueprints

Tracing
Trace – sounds surprising, right? This is what it really means:

  1. Insert the scan in the AutoCAD file, as an image using the option ‘Insert Raster Image Reference’
  2. Drag the image to the desired origin
  3. Zoom Extents
  4. Align the image to a perfect X and Y axis
  5. Choose 5-10 lines in the X axis whose measurements are mentioned
  6. Dimension those lines using the ‘_dimlinear’ command’
  7. Scale the drawing so that the actual measurements and the AutoCAD dimensions match
  8. Repeat (5) and (6) and see if dimensions and measurements in Y axis match
  9. If not, this means that the scan is imperfect, or the print was taken with the command ‘Fit to Paper’ or ‘Stretch to Paper’, and the ‘Preserve Aspect Ratio’ box was unchecked
  10. In such a case, use Stretch command to scale the Y axis only to make the measurements and dimensions match
  11. Check dimensions and measurements over 5-10 places in both X and Y axis again
  12. If okay, we begin by drafting the AutoCAD drawing by drawing lines over the Raster Image below. It saves us the trouble of drafting each line afresh
  13. If not Okay, we abandon the trace process and proceed to the next process:

Drafting

In this case a fresh AutoCAD drawing is drafted, by viewing each and every measurement mentioned in the scan

 Rasterization

Most of us know that a scanned document can be directly converted to a Word document by an OCR scanner – a process quite popular in Research, Records and Legal documentation.

On the same lines, there are, of recent, software that converts the raster to vector that lead to a DWG or DXF CAD file.

Checking

Special points to look out for during Paper to CAD conversion, which are covered in a separate blog Quality Assurance in Architectural PDF to CAD conversion Service

Principally, extra Quality checks in Conversion involve looking out for:

  • Errors due to visual misinterpretation of the input drawing
  • Cross checking the output line for line with the input
  • Scale
  • CAD standards, especially layer management

Queries

It is more important to put up queries in Architectural PDF to CAD conversion jobs than in drafting or design jobs. This s because the queries mostly deal with poor legibility of the scan/paper, or missing information. Such information CANNOT be inferred by architectural intelligence or experience. It simply has to be asked.

Considering the number of building from the pre-CAD era existing in the world, one envisages a huge volume of CAD conversion jobs in the immediate future: enough to create a specialized industry out of Architectural PDF to CAD conversion.