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Quality

Over the years, we have developed new and better ways to prepare the kind of CAD documents our clients need. The three most important are accuracy, completeness and quality assurance.

Accuracy

This is the degree of positional closeness of the CAD linework to the source drawing. Many old and softer originals contain distortions that are captured by the scanning process. These include linear and axial stretching, angular skewing, and spherical displacements such as  pin-cushioning and barreling. Long originals and cloth-like materials are particularly susceptible to these distortions.
To correct for drawing geometry deficiencies, we usually construct a vector grid using CAD lines and keyboard entry to ensure accuracy, always using the written dimensions from the original document. In some instances, such as site surveys and maps, we actually construct the property lines or municipal boundaries using bearings and distances to create the accurate control points needed. Next, we underlay the raster file and register it to the constructed vector control points. As an example, the illustration below shows a 10″x10″ vector grid in red, registered to a scanned image of  various aircraft part details from 1976. The original Mylar sheet was 36″ x 139″ in size.
Next, we identify every grid intersection on the scanned image and reposition it to the correct location shown by the accurate vector lines. With all source and destination points defined, we run our image processing software to actually remove the distortion or  “rubber-sheet” the image to the correct geometry. This corrects for inaccurate positioning due to stretching, angular irregularities, and differential x-y scaling.  The image is now ready for vector conversion. Below are close-up views of an intersection before and after correction. Of course, after conversion, the control grid is discarded and does not appear in the final deliverable.

Completeness

This step ensures the successful transfer of all data from the original paper drawing to the CAD file. Without proper controls, linework and annotation information may not be converted completely to CAD either by omission or by misinterpretation. Overlapping linework and text in the source document is the main reason we use CAD operators and interactive conversion instead of software-only solutions. Only the human eye can interpret obscured text written over lines or hatching patterns. Typical errors include missing text, dimensions, and even misplaced or unconnected linework.
Correct interpretation of drawing data during the transfer to CAD is part of the equation as well. Typical interpretation errors include incorrect CAD layer utilization and poor adherence to established CAD drafting standards, including line type, color, and weight, font style, text size and fractional stacking style in dimensions. We designed our own software to check for all these items, one layer and one object type at the time. Any errors found are then corrected by an experienced CAD professional prior to delivery. For example, the hospital floor plan from 1994 shown below contains  over fifteen layers, such as:

A-ANNO – Architectural notes
A-DIMS – Dimensions
A-WALL – Full height walls
A-CLNG – Ceiling grid
A-DOOR – Doors and Frames
A-GLAZ – Windows, glazing
A-CSWK – Casework, shelving
A-FLOR – Floor level features
A-STRS – Stairs, handrails
A-EVTR – Elevators
A-EQPM – Medical equipment
S-GRID – Structural grid
S-COLS – Structural columns
P-FIXT – Plumbing fixtures
M-EQPM – HVAC equipment
E-POWR – Power outlets
E-LITE – Lighting fixtures

Quality Assurance

This step ensures the successful transfer of all data from the original paper drawing to the CAD file. Without proper controls, linework and annotation information may not be converted completely to CAD either by omission or by misinterpretation. Overlapping linework and text in the source document is the main reason we use CAD operators and interactive conversion instead of software-only solutions. Only the human eye can interpret obscured text written over lines or hatching patterns. Typical errors include missing text, dimensions, and even misplaced or unconnected linework.
Once the conversion to CAD work is complete, the Quality Assurance phase begins. It is the last stage in the production process, but certainly, one of the most important components of the whole. QA is a highly structured process, guided by experienced and knowledgeable CAD professionals. We have developed software specifically geared for the task, but ultimately, it relies on human experience. QA makes our CAD files ready for integration into your CAD/BIM workflows.
Our Quality Assurance process consists of three sequential steps. These are illustrated above on a site detail scan dating back to 2002. We converted it to CAD in 2016. Each panel from left to right corresponds to one of the three QA steps below.
  • SCAN INSPECTION – Review source scan to understand and assess the contents of the original drawing. Research marginal data.
  • OVERLAY COMPARISON – Methodically toggle on and off the overlaid CAD and image, then check and tag each item individually.
  • CAD CORRECTIONS – Correct the CAD data by addressing each tag instruction. Verify all discovered errors were corrected.
Scan Inspection
The first step consists of reviewing the original source data to understand the contents of the drawing. Of course, this is also done by the technician doing the initial CAD conversion work, but this step adds a second set of eyes looking at the data. This ensures nothing is missed or misunderstood. During this step we usually discover items that are not entirely clear, either the image is somewhat obscured or dimensions simply do not add-up. We call these items “marginal data”. The team collectively decides what the barely legible word should be or how to solve the dilemma of incorrect dimensions. Either way, the end result is a CAD file that is as free of errors as humanly possible. If any item cannot be safely converted to CAD, then it is tagged with a red rectangle and identified as “illegible” to the client.
Overlay Comparison
The second step consists of running though the CAD file contents, one CAD object at a time, to compare it to the underlying scanned image. This superposition plus our software’s ability to very easily toggle the overlay on and off, allows the QA reviewer to determine the accuracy, completeness and correctness of the CAD data. Once verified, the individual item is tagged by a single click, which creates a temporary black background rectangle that identifies the CAD item as “checked and passed”. This assures no object is missed and eliminates repetitive and unnecessary double checking.
CAD Corrections
Finally, the last step includes the actual corrections to the CAD data. By using the tags embedded in the file, our CAD technicians move though the contents very quickly and perform any corrections as identified by the QA manager. These may range from simple layer changes and correcting typos or misspellings to more substantial redrafting tasks, if needed. Occasionally, discovering an incorrect dimension triggers a substantial edit operation that may affect a large portion of the drawing. In fact, an error discovered in one drawing sometimes affects several other drawings, which we correct as well. An example of this is a dimensional error discovered in a multi-level building, where all upper floor plans must be edited to maintain correct “stacking” from floor to floor.