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 center 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 dropdown 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 its 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 Measured To 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 height values. Users have the option to input ellipsoid or geoid heights.
If the chosen vertical datum is none, users are able to provide the ellipsoid height by default.
Whereas if a specific vertical datum is selected, users will have the option to use AHD height values.
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.