A key use of drones is to provide periodic aerial imagery at construction sites to easily monitor weekly/monthly construction progress. A flight was conducted at Queen of Peace Catholic Church in Gainesville, FL where a new Administration building is planned. Parrish-McCall Constructors, Inc. is the general contractor. The flight was conducted during the early stages of the project when utility lines had been re-located and the terrain leveled and graded.
As part of pre-flight mission planning, Google Earth was accessed and its Polygon Tool was used to approximate the area of the site. As depicted below, the project area (outlined in yellow) was estimated to be 0.36 acres.
For relatively small sites such as this, the optimum flight mode was chosen to be a Point-of-Interest (POI) autonomous flight, whereby the drone is programmed to fly a circular loiter pattern about the center point of the site. The flying altitude, radial offset from the center point, and camera look-down angle are selected such that the entire site is always in view during the circular loiter.
To perform the flight, the
center point of the project area was approximated and marked with a tri-pod. The drone was then flown directly above the
tri-pod at an altitude of 50 meters to take a “top-down” (nadir) photo of the site. (Following the flight,
this photo was imported into ArcGIS and geo-referenced to the site coordinates.) After the nadir photo was taken, the drone was programmed
in-flight to perform the POI flight about the
tri-pod at an altitude of 30m, radial offset of 26m, and 5 m/sec ground speed. The drone performed sixteen, highly-repeatable
loiters during which time several minutes of video was recorded. Over 50 photographs were then captured while continuing to
loiter, with the camera programmed to take photographs ever two seconds. This 2-sec photo rate provides a high degree
of overlap that allows the photos to be imported into photogrammetry software
to render orthomosaics, digital surface models (DSM), 3D textured meshes, and 3D point clouds.
Below is a GIS map produced following the flight depicting the drone flight path and locations where photos were taken. The geo-referenced nadir photo is evident in the map.
Below is a GIS map produced following the flight depicting the drone flight path and locations where photos were taken. The geo-referenced nadir photo is evident in the map.
The 50 photos were then processed with photogrammetry software and imported into ArcGIS for final processing. The resultant orthomosaic, DSM, 3D textured mesh, and the 3D point cloud are shown below. The orthomosaic nicely depicts the composite aerial image formed from the 50 photos; the DSM, shown with 1-meter contour intervals, clearly distinguishes the heights of the buildings, trees, and bushes from the graded terrain; the point cloud and the textured mesh provide illustrative 3D representations of the site.
The textured mesh and point cloud can each be interactively panned, zoomed, and tilted. An online map illustrating this capability for the point cloud can be accessed at Interactive Point Cloud Web Map. A video of this capability for the textured mesh is shown below.
An interactive online map is accessible at Construction Site Map. At the interactive map, click on a photo point feature to display the photo. (Note, geo-referenced nadir photo not included in the online map). Below is a brief video from the flight.
