Different Ways to Process AeroPoint Surveys and Expected Accuracy


AeroPoints are smart ground control points that use a built-in GPS to record location data while you fly your survey and are capable of being used anywhere in the world where there is solid ground and open sky. If they are within the range of our Corrections Network, AeroPoints will automatically deliver survey-grade accuracy. As such, we suggest you use the Propeller Corrections Network (PCN) for processing if you can.  However, there are a number of other methods you can use to process AeroPoint data if you are outside of the Corrections Network that have different requirements and offer varying levels of accuracy.

To obtain accurate data, AeroPoints must be powered on and record data for a certain period of time, which differs between AeroPoint 1s and AeroPoint 2s.  If you are unsure if you are using an AeroPoint 1 versus an AeroPoint2, check if there is a charging port.  AeroPoint 1s do not have a charging port, while AeroPoint2s will have one.  

For AeroPoint 1s using the Propeller Corrections Network and the Known Point Method, you must be logging data for at least 45 minutes. AeroPoint 2s need 10 minutes of data capture time using the Propeller Corrections Network or 2 minutes if you are using the Known Point Method. If you are able to leave your AeroPoint(s) to log data for longer, this can increase your survey accuracy, as the AeroPoint is able to collect more positioning data the longer it is left on. 

AeroPoint Model PCN Processing Known Point
AeroPoint 1 45 minutes 45 minutes
AeroPoint 2 10 minutes 2 minutes
Mixed Fleet 45 minutes 45 minutes

 

Please note that AeroPoints cannot be moved during the survey and need to maintain a clear view of the sky. Watch our AeroPoints Essentials video to learn more.

AeroPoints have both a global accuracy (how well a point on a map corresponds to a real-world coordinate system) and an internal accuracy or relative accuracy (how well that point corresponds to other locations on that same 3D survey). 

There are multiple ways to process AeroPoints with Propeller, which can vary in accuracy, as detailed below.

Propeller Corrections Network

If you’re flying within the Propeller Correction Network, you can take advantage of our fully automated post-processing.

Automated processing is the simplest way to use AeroPoints, ensuring, in most cases, a short turnaround time of fewer than 24 hours and all the efficiency benefits AeroPoints provide.

Please note that some Continuously Operating Reference Stations (CORS) experience delays in providing data for automated processing. Our support team will automatically be informed once an AeroPoint survey has been waiting for correction data for more than 24 hours so we can look for other correction sources within range.

With this method, you need to lay the AeroPoint(s) down in a place with a clear view of the sky and away from any potential sources of obstruction, such as trees, powerlines, vehicles, and buildings. Read more for tips and best practices for AeroPoint placement.

Expected Accuracy for this method:

  • Global accuracy:  the best available—20mm/20mm/50mm
  • Consistency: the best available—20mm/20mm/50mm
  • Internal accuracy: 10mm or less — precise internal reconstruction

Known Point*

*Where known point data is supplied to correct AeroPoints, results will depend on the supplied data's accuracy. 

For sites using a local grid or calibration, a known point is needed to process AeroPoint data. To use this method, at least one AeroPoint must be placed on a known survey mark or benchmark location so we can correct your AeroPoints to positions in your local site coordinates. 

Be sure to place this AeroPoint first and pick it up last.  It must be recording data for the entirety of your flight. We can then use this AeroPoint, combined with the known coordinates of that point as the reference point for the other AeroPoints used in the survey.

For the most accurate information, you should not take a location measurement when AeroPoints are capturing data or standing near your known point with a rover during your survey.  This can cause GPS interference, resulting in inaccurate known point readings.

You can also use this method to supply corrections for surveys that are not on a local grid or calibration but happen to fall outside of the service area of the Propeller Corrections Network.

Expected accuracy for this method:

  • 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

If you don’t have access to traditional survey equipment to obtain coordinates for a known point/benchmark, you can also consider using AeroPoints to establish permanent ground control points across your site.

RINEX upload*

*Where RINEX data is supplied to correct AeroPoints, results will depend on the supplied data's accuracy. 

You might have access to a dual-frequency L1/L2 RTK rover, or the site may have an RTK base station receiver. Provide us with RINEX formatted GNSS observations for your survey period, and we can use that as the reference point.

Please note that the RINEX file must have an accurate location for the base in the header as this is the location that the AeroPoints will be measured against.

We need RINEX version 2.11 with a minimum frequency of one observation every 10 seconds. It must cover the whole survey period, and have no gaps longer than 10 minutes. It must also have an accurate position header.

Expected accuracy for this method:

  • Global accuracy: the best available, 20mm/20mm/50mm
  • Consistency: the best available, 20mm/20mm/50mm
  • Internal accuracy: 10mm or less — precise internal reconstruction

Summary

This table compares the accuracy and time requirements for the different ways of using AeroPoints.

Unreferenced Processing Method

The unreferenced processing method uses the approximate GPS coordinates of one of the AeroPoints laid out as the reference point to determine the positions of the rest of the AeroPoints in the set.

This is only recommended when internally accurate control points are required, but there is no need to tie into an existing coordinate system or site control. The AeroPoint coordinates will be very accurate relative to this reference point. However, they will not be referenced to a known survey datum such as US State Plane, Australian MGA grid, or a local site coordinate system.


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, the Propeller team may be able to help. You can contact our support team by clicking the support tab on the top-right pane of your user portal.

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