3DEO announces new US patent for Agile Geo-referenced Scanning.

The collection area is partitioned into ‘polygons’. Simple flight lines are chosen based on these polygons. AGRS enables the lidar to be pointed within the bounds of the polygons, no matter the shape, even as the plane flies in a straight line. In order to optimize collection efficiency, the pointing system needs to be agile. 3DEO engineers accomplished this by using multi-axis scan mirrors to direct the laser beam towards the polygon, wherever that might be in relation to the airplane.

How it works

The major components of AGRS are the two-axis scan mirrors, the mirror controller software, and the electronics connecting the hardware to the software. In essence, a computer controls how to move the mirrors to the right position to point towards various target polygons in an ordered manner. These adjustments use information from the inertial navigation system and lidar system to compensate for any aircraft motion such as roll. These mirror adjustments happen constantly in flight, as each polygon is scanned several times from different angles as the aircraft passes overhead.

During a collection, the AGRS software searches a queued list of polygons for the best one that is within the lidar system’s field of regard (FOR). Even if the polygon is behind the airplane or only a part of it is within the FOR, scanning can begin. To maintain uniformity of point density in the data products, the scanner moves at a constant speed. Once scanned, the polygon is placed back into the queue and the next polygon is selected. Single polygons will be revisited and scanned multiple times in one flight line.

Designing a collection

Airborne mapping collections are typically designed by laying out many parallel swaths on the ground to completely fill the region of interest to be mapped. Each swath is broken into many polygons to be scanned. Swaths typically have some swath overlap to aid registration between polygons. Swaths may be collected from opposite headings; with 3DEO’s side-tilted systems, these opposite headings further increase angular diversity. AGRS enables system operators to engineer the collection parameters to meet customer requirements efficiently.

Why angular diversity matters

The accumulation of scans from different headings and positions along a flight line increases angular diversity. Collecting from several angles increases opportunities for the laser to poke through gaps in complex, partially obscured scenes. Places like forests or urban centers with many tall buildings often have dark voids in point clouds because of shadowing of the laser beam by opaque surfaces. High angular diversity increases the number of angles of interrogation and increases the number of points on the ground, stems of trees or sides of buildings.

Collecting only what matters

The division of targeted areas into polygons concentrates scanning to collect only desired areas of interest, without wasting time collecting areas outside the region of interest. Polygons can be designed to form any convex shape, avoiding unwanted areas or overlapping in particularly important areas to get double or triple data density. AGRS provides flexibility that allows more scans in certain polygons and fewer scans in others. For example, if there is a stand of trees in a relatively open field, more scans of the trees can be collected to get detailed information from the scene. The result is simplified flight lines and efficient collections that focus on the most valuable areas.