Mapping

HOW IT WORKS:  Mapping flights are flown autonomously.  The drone is programmed to fly a grid pattern, much like plowing a field, automatically taking a lot of overlapping pictures.  The distance between swaths and the frequency of taking pictures is dictated by the altitude above the ground and the required front-lap and side-lap.  Typical altitudes are 75 to 250 feet and overlaps in the 60-80% range.

                Altitude            Overlap                  Pictures per acre
                250 feet               60%                                     4
                125 feet               70%                                   20
                75 Feet                 80%                                 100

20 images may not seem very big, but if a project is 100 acres, this is 2000 images.  Once the images are collected they are submitted to a software program that looks for points in the images that are common to 2 or more images.  Since images overlap, there will be lots of these point (typically many many 1,000s).  These points are used to merge all the images into one large image called an orthomosaic.  It is geometrically correct and can be used to measure distances. It is an accurate representation of the earth's surface, having been adjusted for topographic relief, lens distortion, and camera tilt.  The computer process is very complicated, and, in addition to the orthomosaic, results in the creation of a point-cloud, a DSM (digital surface model) and files for 3D imaging.  It is extremely CPU intensive and depending on the computer and number of images, can take minutes to hours.

Special Note:  North Georgia Drones is not a surveying company.  The orthomosaic and other images we create are accurate within themselves but are not georeferenced.  This means that the latitude/longitude of points on the images are not aligned to the World Geodetic System (WGS).  Alignment errors could be in range of 2-3 feet range.  If the images are to be used for surveying purposes (defining boundaries and absolute positions on the ground, then georeferencing is required.  This is usually done by placing ground-control-points (GSD), that are visible to the drone camera, within the mapping area.  These are placed by a licensed surveyor who the determines the exact WGS location of each GSD.  These points are used to georeferenced the maps to the correct earth latitude/longitude.  It requires at least 3 or more GSDs points to correct the orthomosaic map to the WGS.  NGD does market our services to licensed surveyors who can place ground-control-points (GCP) to enable geo-referencing of the images.

BENEFITS:  Depending on the terrain and size of the track, it can take a team of surveyors’ days or weeks to do what the drone can do in less than an hour.  The saving in time and labor cost are significant.  The ability to collect data using a drone can also impact safety by avoiding sending personnel into situations that could be potentially hazardous.


Large Mapping Project

North Georgia Drones conducted an aerial mapping of 140 acres.  A grid pattern flown at 135 feet resulting in 1,961 images.  These images were processed on software from Pix4D.  The result was the creation of the following:

  • Orthomosaic image   Provides a very accurate geometrically correct image of the site and can be used
                                                 for measurements
  • DSM images                 Provides elevation data for all areas of the site
  • 3D mesh                        Provides a 3D prospective of the site
  • Animation                     Fly-through of above 3D mesh


The 3D mesh below can be rotated, moved and zoomed.  Use the mouse left-button to rotate the image.  Use the right-button to move the image.  Use the scroll-wheel to zoom in/out.  It is a little tricky, but with a little practice you will get it.  The orthomosaic and DSM (digital surface model) are very large (10231 x 9782 pixels) images and too big to display in a website.
DSM
Orthomosaic

3D Mesh
Animated fly-through of above 3D mesh
Volumetrics
North Georgia Drones can carry out surveys to determine the volume of material stockpiles, amount of material removed from excavations and quarries, the capacity of dams and the amount of airspace remaining in landfills.  The image below is part of a survey taken of a construction site.  The mapping includes both nadir imaging and altitude date.  From this we can calculates the volume of a pile of extra dirt left from leveling the site.  This enabled the contractor to attach a value to the pile and how many truckloads will be needed for its removal.

Volumetrics can be performed on any area of a site survey or separate drone flights be flow only over an area if interest.  It is also possible to calculate changes in the distribution of soil by comparing data taken before and after soil is moved.  This can be useful in verifying contractors claims.

Mapping
Mapping of a North Geogia Mountain Lake

      Area Covered:  67 acres
      Altitude:  250 feet
      Image Type:  Orthomosaic & DSM
      Images Taken: 580
      GSD: 1.27 inch/pixel
      Orthomosaic size 19025 x 20728 pixels = 394 MegaPixels
Mapping
Mappoing of Canton GA Commerical Property

  Area Covered: 54 acres
  Altitude:  200
  Image Type:  Orthomosaic & DSM
  Images Taken:  933
  GSD .97 inch/pixel
  Orthomosaic size 9303 x 11779 pixels = 110 MegaPixels
Mapping
Mapping of an East Atlanta property

     Area Covered: 12 acres
     Altitude: 135 feet
     Type image:  Orthomosaic & DSM
     Images Taken : 169
     Type: Orthomosaic (24545x8510 pixels =  209 Megapixels)
     Ground Sampling Distance (GSD): .71 in/pixel
Mapping
Mapping of a norheast Atlanta Church

     Area Covered: 10 acres
     Altitude: 100 feet
     Type image:  Orthomosaic
     Images Taken : 339
     Type: Orthomosaic (11694x10979 pixels =  128 Megapixels)
     Ground Sampling Distance (GSD): 0.65in/pixel