How Accurate is theEngine?


Accuracy and file size limits are important considerations when processing polygons or polylines from incoming spatial data. The question is, how well do the output coordinates match the incoming, and how many records can you get into one file?

The following extracts are zoomed-in views from two shapefiles in ArcView. One file is the polyline CAD and the other is the polygon shapefile made by theEngine from the polylines. The polyline file lies on top of the polygon file.

The incoming data has about 8,000 polyline records. This was automatically converted to 3,000 polygons in roughly 30 minutes with theEngine, and written to a polygon file. Click here to see the full parcel map

The CAD polylines are from a city CAD department archive and were drawn with many small line segments representing propery line and street borders, a typical CAD operation. It was purported to be clean, and it was pretty close, but not exactly dead on.

To test the accuracy of conversion, we simply zoomed into common vertices of the lines and polygons. Where they begin to diverge is the point at which a tolerance exist between the two. The following are screen captures of the zoomed-in shapefile along with map units in feet.

Zoom into about 1/5 of the file...

Then into just a few polygons...

Then into a corner...

And finally until we can't measure anymore... remember both lines and polygons are visible!

There is no discernable coordinate shift between the vertices of the polylines and the polygon, even at 0.000001 feet. theEngine uses the coordinates given it without distortion. And since theEngine has the capability to append as you go or later on, there is also no file size limit either.

By the way, there is a tool in theEngine for finding these dimensions... in case you were wondering.