We are continually updating this document. If there is any information that you would like us to add or change, or if you have questions, please contact SiteSee Support. Thank you.
SiteSee uses AprilTags to automate the processing of ground control points (GCPs). Like QR codes, AprilTags use a computer-generated pattern to encode information, but their pattern is simpler and can thus be recognised by our processing software from a greater distance:
Operating the AeroPoints
Each AeroPoint includes a solar panel, battery, GPS and WiFi inside a sealed, rugged shell.
Prior to first using them, each set of AeroPoints must be activated. To do so, go to propelleraero.com/activate-aeropoints and enter the unique 8-character code included with your AeroPoints set. Under ‘Portal Name’, enter the business/entity you wish your AeroPoints to be assigned to.
You may be prompted to log into your Propeller account before activating your AeroPoints. If you don’t have an account, you can register for one at app.prpellr.com/accounts/register.
Placing and Starting the AeroPoints
Once you have correctly mounted each AprilTag onto its corresponding AeroPoint, you are ready to place them and start logging data.
If your AeroPoints are new, or if you have not used them in a while, make sure they are fully charged before you use them. To do so, ensure they are turned off and place them in a sunny location, angled with the solar panel in the top left/right corner. It takes about seven hours in sunny conditions to reach full charge.
Use a damp cloth to wipe any dust, mud, or grime from the solar panel located at the top of the AeroPoints. This will ensure maximum charging efficiency.
While our processing software only requires 3 GCPs, we strongly recommend you always use all 5 AeroPoints. The quality of the position data logged by each AeroPoint depends on how well it is placed and how much time it has available to log data. Using five AeroPoints increases the likelihood that there will be at least three usable GCP datasets - even if the data logged by one or two AeroPoints happens to be of insufficient quality.
Place the AeroPoints as follows:
Evenly distribute them around the tower at a distance of about 5 to 10 meters (15 to 30 ft) from the tower. If this is not possible, you may place them on one side of the tower. Avoid placing several AeroPoints in a straight line.
Place the AeroPoints so that during capture of the tower all of them will be in full view of the drone at least some of the time. Bear in mind that when performing the mission flights, the AeroPoints must be captured simultaneously, so do not move are move them until the capture is completed.
Ideally, if the site conditions allow it, all AeroPoints should have an unobstructed view of the sky in every direction above a 15° angle (see image below). Where possible, avoid placing AeroPoints near trees, walls, buildings or power lines.
Avoid placing AeroPoints where they will be disturbed by people, animals or vehicles. Let other people nearby know that AeroPoints are in use.
Immediately after you place each AeroPoint, check that its AprilTag is still properly aligned/centred, then press its button to start recording. The button’s red light will turn on, indicating that the AeroPoint is now logging its position. AeroPoints will begin recording data 60 seconds after you press the button to start. Do not change the position of an AeroPoint after this time.
Best: GCP placed on top of cabinets and vehicle
Good. GCP are placed away from tower. Trees need to be avoided.
Wrong. GCP are too close to tower which is causing a shadow.
If you change your mind about the position of a AeroPoint and want to start over before a mission has started. Just push the button once to stop recording, move your AeroPoint, then push button again to start recording. Recommended to wait a minimum of 5 minutes before starting recording again. It is highly reccommended to avoid the situation where you need to move it as it can cause inaccuracies in the results.
Made a Mistake During a mission?
Where it is impossible to use AeroPoints (e.g. dense tree cover, etc.), a 5-meter surveyor's staff such as the one below can be used instead to improve the accuracy of the 3D model by calibrating it to the known staff length during processing. Put the fully extended staff on the ground or against the tower so that it appears in as many images as possible.
Collecting the AeroPoints
Each AeroPoint should be left in place to record at least 60 minutes of data. The longer it is left in place, the more accurate the position it records. Where it is impossible to place the AeroPoints with an unobstructed view of the sky (see the previous section for details), they should be allowed to record for at least about 1.5 hours. After five hours AeroPoints will automatically turn themselves off (sleep mode).
To maximise recording time, we recommend you place all AeroPoints immediately after arriving at the site (i.e. before carrying out pre-flight drone checks and planning the flights) and finish flying and packing up your drone before collecting the AeroPoints.
Collect your AeroPoints in reverse order to how you laid them out (i.e. pick up the last-placed AeroPoint first and finish with the first-placed AeroPoint). Before you pick up each AeroPoint, press its button to stop logging data. You can now remove the AprilTags from the AeroPoints.
When you press the button to finish recording, the AeroPoint enters WiFi search mode, indicated by the button light flashing once every 30 seconds. In this mode it will search intermittently for a WiFi network called ‘propeller’ with the password ‘propeller’.
Note that the WiFi network name and password the AeroPoints are scanning for cannot be changed. For the AeroPoints to be able to connect to your WiFi network, make sure that your network’s name (SSID) and the password are both set to ‘propeller’.
Unlike Android devices, iOS devices don’t allow direct setting of the Personal Hotspot WiFi network name (SSID). Instead they automatically use the device name. To change the device name go to Settings > General > About > Name, then change the name of your device to ‘propeller’.
If the AeroPoint finds a WiFi network named ‘propeller’ within 24 hours, it will connect to it automatically and upload all recorded data. This mode is indicated by a slow blink (connecting) followed by a fast blink (uploading) of the button. It takes approximately one minute to upload each hour of recorded data (but can take longer if you have a slow connection). Once the upload is completed, the button stops flashing.
If the AeroPoint cannot find a suitable network within 24 hours, it goes into sleep mode. To wake it up and start looking for a network again, press the button twice (the first press turns on ‘recording
mode’, the second press switches it to ‘WiFi search mode’).
AeroPoints can store GPS data from at least 100 surveys before requiring upload (useful when doing multiple surveys in remote areas). Data from different locations will be grouped automatically by the Propeller platform.
Processing the AeroPoints
After uploading all AeroPoint data, proceed as follows:
1. Open the AeroPoints processing portal
On your PC, log in to your Propeller portal, and click ‘AEROPOINTS’ in the top navigation bar. On the left in the menu titled ‘Your sets’ you will see a list of all your AeroPoint sets. Select a set to see the unique ID code associated with each of its AeroPoint units, along with the time of the most recent upload, and the battery level recorded at that time. In the section ‘Your flights’ underneath, all surveys recorded by the selected set are listed (sorted by date):
2. Check all uploads are complete
Scroll to the site you want to process and check that all AeroPoints have uploaded (i.e. are shown on the map and the button is labelled 'PROCESS NOW'):
You can click on the site to get more information about each AeroPoint. If any of your AeroPoints is missing, the upload may have failed. In this case, repeat the upload procedure as described in the previous section.
3. Process site
Click ‘PROCESS NOW’ which will display the processing options and select ‘Propeller Correction Network’. Blue circles will be displayed that show whether your site is located in an area covered by the Propeller Correction Network:
If your site is covered by the network, select your preferred Datum (in Australia, please select GDA2020), then click ‘PROCESS’. The map is shown again, displaying 'Waiting for correction data':
If your site is not covered by the Propeller Correction Network (i.e not located within blue circles), please contact SiteSee Support for advice regarding which of the other methods might be suitable for your site.
When you return to the 'Your flights' list, 'AWAITING CORRECTIONS' is displayed for this site:
On completion of processing, Propeller will send you an email notification. Instead of ‘AWAITING CORRECTIONS’ the button of this site is now labelled ‘DOWNLOAD’:
On the map, AeroPoints that have recorded low-quality data are displayed with a red border. If more than two of your five AeroPoints are red, contact SiteSee Support.
Depending on location and Propeller network coverage, processing can take from minutes to several hours.
4. Download GCP data
Once the site has finished processing, click on ‘Download’ and download the following files (you will need these files when you upload your image files):
- CSV (i.e. not the simple version)
Preparing the AprilTags
Printing the AprilTags
Click on each of the following files to download them:
Follow these steps to get the AprilTags printed:
- Click on each AprilTag to download the full-size PNG file.
- Once you have downloaded all five AprilTag image files, submit them to a good-quality printing service of your choice. Instruct the printing service to print the images to the following specifications (consider using the draft email provided at the end of this section when sending your quote request):
- Material: Corflute 5 mm white (do not use PVC)
- Ink quality: weather and UV resistant
- Laminating: lustre or matte (i.e. avoid any kind of glossy or reflective laminating)
- Resolution: 300 DPI, which will result in printed tag dimensions of exactly 490 mm by 490 mm (explain to your printing service that in order to obtain the correct AprilTag dimensions it is important that they print at exactly this resolution)
- Eyelets in each corner with a diameter of about 6-9 mm (0.25 - 0.35 inch), about 10-15 mm (0.4 - 0.6 inch) away from the corners
- When you receive the printed AprilTags, check that they measure exactly 490 mm by 490 mm (+/- 3 mm) or 19.3 by 19.3 inches (+/- 0.1 inch). The AprilTag pattern itself should measure 400 mm by 400 mm (15.7 by 15.7 inches).
We would like you quote on the following:
- 1 print of each of the attached designs (i.e. 5 prints in total)
- Material: Corflute 5 mm
- Ink quality: weather and UV resistant
- Laminating: lustre/matte
- Resolution: 300 DPI, which must result in print dimensions of exactly 490 mm by 490 mm (it is very important that these dimensions are accurate, so please print at exactly the specified resolution)
- Eyelets in each corner with a diameter of about 6-9 mm, about 10-15 mm away from the corners.
Preparing the Cutouts
Use a carpet knife to carefully cut out the openings for the AeroPoint solar panel and button. Your finished AprilTags should look like the one below.
The position of the AeroPoint button can vary due to manufacturing variability. While the cutout mark for the button will fit most AeroPoints, it might not be positioned correctly for your particular set of AeroPoints. We therefore recommend you verify that your buttons are positioned as shown in the image below (i.e. 38 mm/1.5” horizontally and 148 mm/5.8” vertically from the AeroPoint centre) and adjust your cutouts if necessary.
Mounting the AprilTags
Mounting: Use string or elastic cord to mount the AprilTags onto the AeroPoints. The material you use should be sufficiently strong to hold the AprilTag taut against the AeroPoint so that it cannot be moved by wind gusts. Also, the material must be white so it blends into the white tag margin. By way of example, at the end of this document, the method used by SiteSee is described. However, your approach might be different depending on materials available to you.
Centering: Use the four grey markers around the edge of the AprilTags to carefully align them with the black and white fields of the AeroPoints. This will ensure that they are centred precisely.
The AprilTags and AeroPoints can be stored in the same bag.
AeroPoints are built tough, but you can extend their life by keeping them clean and dry when not in use. Simply remove dirt and dust with a damp cloth as soon as practicable once your job is complete.
AeroPoints are water-resistant (they can handle some mud, splashes or light rain) but not waterproof (they should not be submerged or left out in heavy rain.
Reduce the risk of sand or gravel scratching the solar panels by stacking and storing AeroPoints with the undersides together (as shown below).
AprilTag Mounting Method Example
This section describes the method used by SiteSee to mount AprilTags onto AeroPoints. Depending on the materials available to you, your method might be different. This is OK as long as it fulfills the following requirements:
- Where it is visible from above, the string/cord material must be white so that it blends into the white AprilTag margin.
- The AprilTags are held taut against the AeroPoints so that they cannot be moved by wind gusts.
Cut a shock cord length of 40 cm (16”). Tie a knot at both ends so that the knots are approximately 30 cm (12”) apart:
Cut a length of blind cord about twice as long as the AprilTag width. Thread the blind cord through the eyelets as follows:
On the back of the AprilTag, tie the blind cord to the shock cord. When finished, the shock cord should be slightly loose as shown in the image below. Repeat the steps above for the other side of the AprilTag. The finished setup should look like this:
Mounted on the AeroPoint, this setup looks as follows: