There are two types of corrections applied to AeroPoints when they are processed using the Known Point method. The first is an external correction, where one AeroPoint corrects its position to some fixed position on the earth - this is the Known AeroPoint. The second step is an internal correction, when the other AeroPoints correct their positions relative to the known AeroPoint.
To use this correction method, follow these steps:
- Place the centre of the Known AeroPoint over a survey mark or another point on the ground which has known coordinates. These coordinates should be in a global projected or geographic coordinate reference system, in the form Easting, Northing, Elevation or Latitude, Longitude, Elevation. Alternatively, survey the top of the Known AeroPoint with a rover to determine its coordinates.
- If you have sent Propeller a local grid calibration file for a Site you have already created in the Viewer, you may use local grid coordinates instead of global coordinates.
- Leave the Known AeroPoint in place for the entire duration of the survey. This means it must be the first AeroPoint placed and turned on, and the last AeroPoint turned off and picked up. This is important because all other points will need to be corrected against this single point at the end of the survey.
- After uploading data from your AeroPoints, click the "process" button for your survey in the AeroPoints portal.
If you have provided Propeller with a local grid calibration file for your Site, you can use the Local Grid correction method. Otherwise, use the Global Survey Benchmark method below.
Global Survey Benchmark
- In the Coordinate System dropdown box, select "Projected" if you have an Easting and Northing, or "Geographic" if you have a Latitude and Longitude.
- If you used local grid coordinates, select the Site which has your local grid calibration set up from the "Site" drop down box. Otherwise, you will need to select the Coordinate Reference System of your global coordinates. If you have trouble locating the right Coordinate Reference System, you can search for it's EPSG code at epsg.io and use the code to find it in the list.
- In the "AeroPoint Capture" dropdown list, select the capture ID of the AeroPoint that was used as a Known Point.
- Select "MeasuredTo" either "ground" or "top of AeroPoint" depending on whether your coordinates refer to the ground beneath the AeroPoint or the top of the AeroPoint. For example, if you placed the AeroPoint over a survey mark, you would choose "ground" and if you surveyed the top of the AeroPoint with a rover, you would choose "top of AeroPoint".
- Select the appropriate units from the Units dropdown box.
- Enter the Northing/Latitude, Easting/Longitude, and Ellipsoid Height in the appropriate boxes. The height must be an ellipsoid, not a geoid height or your results will not be accurate.
Global accuracy: If you place the AeroPoint accurately, the best available, 20mm/20mm/50mm (plus the accuracy of the mark itself)
Consistency: If you use the same known mark each time, the best available, 20mm/20mm/50mm
Internal accuracy: 10mm or less — precise internal reconstruction