Flight Marker Guide

Steps required to create and maintain flight markers

📦 This article has been updated

It’s now part of our improved How to place and maintain flight markers (GCPs).

Place new markers

Step 1. Preparations

Use Flight Marker Map to review the requested flight markers location. There are two ways to do it:

• If you're in the field: view the flight markers on the map using location services on your device. Tap the geolocation button to reference yourself on the map.

• Download the CSV file with flight marker coordinates from a GCP Request email and upload them to a GPS Rover.

If you do not have access, please email uscs@traceair.net.

Gather tools For hard surfaces (concrete or asphalt):

• White spray paint. Approximately one can per 4 flight markers (3 ft in diameter)
• Road marking paint
• Pavement line stencil. 4 inches wide by 4 feet long

​For soil surfaces (dirt or grass):

• Tarp. 6 × 6 ft to underlay markers that have or will likely have significant vegetative growth around the marker over the duration of the project
• For the low wind areas – PVC window blinds. White, vertical, cut into 3 sections (~30 inches)
• For the high wind areas – premade aerial targets. Usually sheet plastic or synthetic (vinyl) mesh fabric; 2–4 ft square. You can find fabric flight markers on Amazon
• Nails. 6–8 inches long (5 nails per flight marker on dirt/grass)
• Hammer

Step 2. Creating Flight Marker

A flat 6 × 6 ft area per flight marker is required to georeference the data correctly. Please prioritize the longevity of the flight marker (prefer hard over earthen surfaces). We suggest making three measurements of each point, reinitializing the GNSS receiver for each measurement, and capturing a photo of each GCP you’ve measured.

⚠️ Please note some recommendations:

• If you want to highlight a GCP for the crew on the ground, place a fence around the point (the fence should not be higher than 4.5 ft) or insert a stick with a red cloth. For both variants, at least 5 ft away from the center of the point.

• Avoid areas with heavy grading work.

• Do not place GCP in pits, on stockpiles, or on slopes.

• Do not place GCP near or on tall vegetation. If vegetation cannot be avoided, please remove the vegetation in the 6 × 6 ft area beneath and surrounding the flight marker or underlay the flight marker with a 6 x 6 ft tarp secured by large spikes.

• Do not install GCP near tall objects (walls, buildings, rocks).

• Do not install a stick within the center of GCP.

• Do not place GCP under trees or power lines.

• Crosses are the preferred way of drawing a flight marker. If you use a chevron, measure its inner corner.

🔔 We understand that optimal locations for flight markers we request may be difficult to access or undergo frequent disturbance. Stay as close as possible (within a 30 ft radius) to the recommended locations. If flight markers need to move a couple of hundred feet out of an active grading area, we can adjust on our end to accommodate this.

Placing markers on different surfaces: Hard surfaces (concrete or asphalt)

Use solvent-based white spray paint on the concrete with a stencil:

1. Cover the washer and nail with a piece of tape
2. Layout the 4-inch asphalt line stencil centered over the nail
3. Spray paint to thoroughly cover the exposed surface inside of the stencil
4. Lift the stencil and rotate it 90 degrees centered over the nail
5. Repeat spraying paint to thoroughly cover the exposed surface inside of the stencil

If you do not have a stencil and you are precise with your paint placement:

Spray paint two 4-inch wide legs at 2–4 ft in length to form a cross through the center of the survey control point (if applicable). Ensure the marker is large enough to be visible from the air.

Soil surfaces (dirt or grass)

We recommend covering the ground with a polyester tarp (or black landscaping cloth) before placing the flight marker. Clear any vegetation within a 6 ft radius around and remove the top level of the soil with grass under the control point, lay a 6 × 6 ft tarp down, and secure the corners with spikes or large nails.

For the low wind areas: PVC window blinds

1. Drill a hole and hammer a nail through the center of two blinds, forming a cross (be careful, plastic is fragile and can easily be broken with excess force)
2. For extra security, drill holes and hammer a nail through both ends of each blind

For the high wind areas: pre-made aerial targets

1. Hammer a nail through the center of the fabric, or place the center of the fabric over a survey control point (if applicable)
2. Hammer a nail through each of the four corners of the fabric flight marker and tarp (if a tarp was placed)

🔔 Before each scan, please verify that flight markers can be seen clearly — i.e., that they are not covered with dirt or vegetation.

Step 3. Flight Markers Upload

File format

We suggest sending us a full survey report of the GCPs measurements (file unloaded from rover) in PDF, XLSX, or CSV format. Flight marker coordinates should be recorded in the coordinate system of the project, matching the design data (OG & DG).

Check report examples:

• pdf_example.pdf
• excel_example.xlsx
• text_example.csv

Uploading file

There are two ways to send a file:

• Upload file in the Pilot app
• Upload file in the Project Portal

Fix markers

Some requested markers need to be fixed or checked. In the Flight Marker Map, they are marked in red or yellow depending on the type of fix. Hover a mouse over the marker to get the specific reason for a requested GCP.

The marker itself should not be touched or moved at all. Even the smallest change in its position will render it unusable for scan processing. Based on our experience, this most commonly occurs during the marker's cleanup process from the grass.

Replace

• Damaged – the point is almost destroyed but still visible. It may become destroyed before the next flight. It needs to be restored to the initial state.
• Undetectable–the point is not recognizable in the drone images. Make the point visible from the air.
• Faded–the point is barely visible. There is a need to refresh the paint.

Clean Up / Repaint

• Obstructed– some objects are placed over the point (rubbish, materials, etc.) Remove the objects.
• Covered by Dirt, Grass, or Snow – the point is covered by dirt, grass, or snow. Clean the marker so it becomes visible.

Check condition

The point is visible and can be used for scan processing needs. Check the condition of the GCP, if it is okay – no actions are required. Otherwise, place a new point instead.

This status is assigned if significant time has passed since the previous scan to verify that all flight markers are still in place and in good condition.

Send coordinates

TraceAir can observe the marker in the scan, but we have not received the coordinates. Please send us the file with marker data.

Remeasure

The "Remeasure" status indicates that the coordinates of a point should be measured again in the global coordinate system.