Posted by: imalqata | February 21, 2013

Surveying for Quantity…and Quality

High Definition Surveying (HDS) at Malqata

Thursday, February 21, 2013

This year, I was able to show the Malqata team the results of a survey I did last field season at the King’s palace at Malqata using a laser scanner.  HDS scanning is a relatively new tool in surveying. As a survey tool, the HDS scanner gathers point data in the same way as traditional survey equipment, that is by measuring angles and distances from known points.  The difference is that the scanner does it at an extremely fast rate, gathering up to 50,000 points per second; most surveyors just cannot move fast enough to do that with traditional equipment. At this rate of collection, millions of points can be gathered quickly to create a 3D computer model of the original features in a cloud of points (called, infact, a “pointcloud”). Because of constraints of the cost of the scanners, along with the computers and software needed to manipulate the extremely large files that are created for the scans, HDS scanning has been slow to enter the world of archaeological documentation although it has been around for about a decade. Still, the potential of the system for recording sites is tremendous.  Scanning provides an accurate record in 3D of a structure at a given point in time and can also be used for additional architectural studies as well as the basis for virtual reconstruction of a monument.

Portion of scanned walls at Malqata.  The dark area in the foreground shows a position of the scanner. This will be filled in with points from other scan locations.

Portion of scanned walls at Malqata. The dark area in the foreground shows a position of the scanner. This will be filled in with points from other scan locations.

For the work at Malqata, the Expedition retained me through my surveying position with Nolte-NV5 of San Diego, CA.  The company was generous enough to let me bring a Leica C10 scanner as part of the survey work I was doing at Malqata, and the results are astounding.  From the combination of multiple days’ scans over about two weeks I was able to gather close to 800,000,000 survey points, each one of them with accurate coordinate and elevation values as established by survey control points done by a combination of conventional surveying and Global Positioning System (GPS).  After cleaning up the data and trimming it to the area of the king’s palace, the number of points on the ground and walls was reduced to only about 574,000,000 points with the points on the walls having an average spacing of approximately 5 millimeters.  This density of points allows for a model with enough detail that individual mud bricks are distinguishable.  Although the pointcloud may look like a photograph at this scale, it is comprised of the millions of points.  So, unlike a photograph, the pointcloud can be accurately used for measurements and can be rotated to be viewed from any angle.

Detail of a portion of the scan showing spacing of points.

Detail of a portion of the scan showing spacing of points.

Although the cleanup and photographic coloring of the HDS scan are on-going, we are fortunate to have accurate and complete documentation of the palace prior to the conservation work that is being done this season, and we have the basis for further studies at this fascinating site.

Joel Paulson

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Responses

  1. Absolutely fascinating and great!!!


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