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How Critical is Your Drone Flight Pattern? Does it Make a Difference?

Here is the mission. The area shown in RED needs to be mapped with 1′ contours and rectified orthomosaic. How many Ground Control Points (GCPs) are needed and what would be the the best way to fly the mission?

Choosing the right drone flight pattern

Area to be mapped
Area to be mapped

Three different flight patterns were flown to determine which method is better. A, B or C?

Drone flight pattern option A
Drone flight pattern option A
Drone flight pattern option B
Drone flight pattern option B
Drone flight pattern option C
Drone flight pattern option C

Several permanent Ground Control Points (GCPs) and check points were placed along the dam for testing purposes.

Overview of Ground Control Points
Overview of Ground Control Points

Six GCPs were selected for balanced aerial triangulation. Then the camera optimization was ran to calculate the RMSE values.

Aerial triangulation example
Aerial triangulation example

The site was flown with a Mavic 2 Pro. Rolling shutter compensation was turned off for the initial comparison results.

Below is the result for pattern A.

Drone flight pattern result A
Drone flight pattern result A

Below is the result for pattern B.

Drone flight pattern result B
Drone flight pattern result B

Below is the result for pattern C.

Note: GCP 1 & 2 was not included in flight pattern C.

Drone flight pattern result C
Drone flight pattern result C

Reviewing the Check Points RMSE values, flight pattern C yields the best result for the horizontal position.

Flight pattern B yields the best result for the vertical position.

———-

Reviewing the Control Points RMSE values, flight pattern C yields the best result for the horizontal position.

Flight pattern C yields the best result of the vertical position.

———-

For this particular mission, flight pattern C was used for the final results.

All control points were used as GCPs.

Without rolling shutter compensation.


With rolling shutter compensation.

Final 1′ contours

Final 1' Contours

The flight pattern along with the right number of GCPs placed in strategic locations is the best solution for 3D survey mapping.

There is always going to be floating error and one solution may not work with every flight scenario.

The trick is to look at the mission flight area and plan accordingly to determine the best approach to minimize any errors.

Different sensors will result in different solutions. Not all drones/sensors are equal.

Remember the deliverables are the key factor. Select the sensor that will meet the deliverables. Select the drone platform that can carry the sensor.

Each sensor/lens combination will have distortion. Calculate the Neat area for each sensor to be able to determine the right sensor for the deliverables. Different sensors will need a different number of GCPs in strategic locations to meet the deliverables.

The higher the micron value “µ”, the more information that can be stored per pixel. Anything above a 1.5 µ is recommended for 3D mapping.

NOTE: The higher megapixel does not always mean a higher µ value. See the chart below.

Conclusion? When it comes to choosing drone flight pattern, doing it right takes some work and planning.

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LearnCST contributor Jim Crume created the Survey Mathematics Made Simple and Survey Mapping Made Simple book series to showcase the technical aspects needed to become a professional design level mapper. 

Previous Article: How to Start a Design Level Drone Mapping Business

How to Start a Design Level Drone Mapping Business

I get asked a lot what I recommend for a startup drone mapping business. Before answering the question we must consider the intent of the operation. After all, there are two types of drone mapping: generic 3D mapping and its much more intricate cousin, design level survey mapping.

3D mapping is done at various levels of accuracy and flying heights mostly with manned aircraft ranging from 1′ to 15′ contour levels. This type of mapping is generally not used by design engineers to create accurate man-made features. It is used for dirt quantities, layout and design of roads, highways, power lines, etc.

The lowest that manned aircraft can fly is at 1000′ AGL which equates to 2.5cm level mapping which is design level mapping but very expensive to acquire.

Design level survey mapping is also 3D mapping however the accuracy is within 0.07′ (2 cm) or better. Engineers and Architects can use this mapping to design man-made features such as buildings, parking lots, streets and so on that require a higher level of accuracy.

Drones can easily capture imagery for design level survey mapping if done right. One button solutions using automated flight software can achieve 3D mapping at various levels of accuracies depending upon the drone camera/sensor and software being used for processing.

Design level survey mapping is the next level which takes more than a one button solution.

Design level drone mapping - our work is our pleasure!
Design level survey mapping – our work is our pleasure!

More Than a One Button Solution

Having surveying knowledge is the key to getting professional design level survey mapping. You need to understand surveying datums such as State Plane Coordinate System, UTM Coordinate System, Ground vs Grid, Grid Adjustment Factors, Geographic Coordinate System, design constraints, grade breaks, planimetrics, contour generation and breaklines to mention a few.

Being a licensed Professional Land Surveyor is a huge benefit. Teaming up with a licensed professional will fill that gap as well.

A UAV (drone) is just a tool and in a surveyors hand is priceless when it comes to design level survey mapping.

Tradition surveying knowledge takes drone mapping to the next level
Taking drone mapping to the next level

Surveying Knowledge is Priceless

You need a drone with a camera/sensor that will meet sufficient accuracy requirements.

  • I use a DJI Mavic 2 Pro and Inspire 2 with a x5s camera/15mm lens.
  • I use the right number of GCPs set in strategic locations using a survey grade GPS to get a solid aerial triangulation solution.
  • I use Metashape Pro to process the imagery and measure the ASPRS RMSE values. Breaklines are created along grade breaks, man-made features and extracted as a DXF file. A rectified orthomosaic is also created.
  • The DXF is imported into Civil 3D to create a 3D surface. Planimetrics are added to create a design level survey map for engineers and architects to use for their design.
Design work overlaid on high quality drone mapping
Design work overlaid on high quality drone mapping

How to start a drone mapping business

I use both an iMac and Windows computer to process all of the data. So how to start a drone mapping business? In conclusion, here is my survey mapping equipment list:

  • Survey knowledge (priceless)
  • Survey grade GPS equipment ($20k+)
  • Mavic 2 Pro ($2k) or Inspire 2 with x5s camera & 15mm lens ($8k+)
  • Mini iPad with Litchi ($400+)
  • Metashape Pro for breaklines and orthomosaic ($3500)
  • Civil 3D to build a surface. ($2400 per year)
  • Computer ($3000+)

Total = $37,300+ to get started

This does not include training, office, vehicle, insurance and all of the other factors it takes to run a business.

As you can see it is not cheap to get into design level survey mapping. It has taken me years to build everything I have to provide this type of service. Working with a company such as Cooper Aerial provides the necessary tools and clients to bring it all together.

You don’t have to have 46+ years experience in surveying but you do need to work with someone that does have surveying experience. Most states in the US require that design level survey mapping be done by or under the direction of a licensed professional land surveyor.

Anyone can fly a drone. Not everyone can deliver design level survey mapping.

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LearnCST contributor Jim Crume created the Survey Mathematics Made Simple and Survey Mapping Made Simple book series to showcase the technical aspects needed to become a professional design level mapper. 

Next article: How Critical is Your Drone Flight Pattern? Does it Make a Difference? 

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