Two types of corrections are applied to AeroPoints when 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—the known AeroPoint.
The second step is an internal correction when the other AeroPoints correct their positions relative to the known AeroPoint.
Steps
1. Place the center of the known AeroPoint over a survey mark or another point on the ground with known coordinates. These coordinates should be in a global projected or geographic coordinate reference system, in the form of easting, northing, elevation or latitude, longitude, elevation. Alternatively, survey the top of the known AeroPoint with a rover to determine its coordinates.
Tip: You can spray-paint the edges of the AeroPoint stencil to make sure you can center the GCP.
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.
2. Leave the known AeroPoint in place for the entire survey duration. 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 must be corrected against this single point at the end of the survey.
3. After uploading data from your AeroPoints, click the PROCESS NOW button for your survey in the AeroPoints portal.
Local Grid
You can use the Local Site Survey Benchmark correction method if you have provided Propeller with a local grid calibration file for your site. This can be a .DC or .CAL file (which can be used to generate a JXL in Trimble Business Center) or a .JXL file. Otherwise, use the Global Survey Benchmark method.
Select the AeroPoint used as the known location and fill out the coordinates.
Global Survey Benchmark
Select the AeroPoint used as the known location and fill out the information.
1. Select the coordinate system from the Coordinate System dropdown box. Select Projected if you have an Easting and Northing or Geographic if you have a latitude and longitude.
2. Users can input ellipsoid or geoid heights.
3. Select the appropriate units from the Units dropdown box. Select the Site with your local grid calibration set up from the Site dropdown box if you used local grid coordinates. Otherwise, you will need to select the coordinate reference system of your global coordinates. If you have trouble locating the right coordinate reference system, search for its EPSG code at epsg.io and use the code to find it in the list.
4. Select Measured To either Bottom of AeroPoint (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." Users can provide the ellipsoid height by default if the chosen vertical datum is none.
You can see what was used to process your AeroPoints in the AeroPoints Dashboard.
Accuracy
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.
I still can't do it!
We wrote these articles to equip you with everything you need to get the job done on your own, but we understand that sometimes this isn't sufficient.
If you're stuck, you can connect with our support team by clicking the support button on the top right corner of your user portal.
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