A lot of things have been happening in the drone Industry. A new company coming up every month with a new concept. New ideas being tested for its feasibility. A lot of these concepts are yet to commercialize or are anywhere near widespread use. But there is one thing that small drones have proved that they can do a very good job at. And that is Aerial photography or simply put capturing photos/videos using a basic camera setup. Couple this setup with an intelligent drone which can do autonomous navigation and you have a powerful tool to do aerial surveys and inspections.
As a prospective business owner or a manager who wishes to explore use of drones in his/her business.You probably have some common question in your mind. And most of the time the drone service providers steer people away from reality by showing them some flashy presentations / videos or assuring them of metrics that they themselves are not sure of in first place.
In this article I hope to give a clearer picture of what expectations one can have by using a drone in his or her field. I may not cover all possible solutions but the ones that are widely used.
You need to answer these questions for yourself.Starting with
INSPECTIONS:-
1. Does your business involve assets that have to be monitored ?
2. Are those assets hard to reach by i.e are they tall , far , tricky to reach?
3. Does photos (and its derivatives) alone solve your inspection problem?
4. Kind of data expected Visual / NIR / Thermal ?
If all your answers are yes then maybe using a drone could be useful in your business. The " maybe " is because of the cost associated with using the drone. As you explore more you would end up with some decisive metrics that you should worry about.
1) Resolution of the images:- Most of the service provides use off the shelf DJI products so take a note of which equipment will be used. Main point to note is the camera specifications like Resolution (generally higher the better ) , Sensor Size ( Higher the better ) , Zoom ( Depending upon how close the drone could fly from the asset choose ; ask for zoom capabilities if you are sure that the drone will not be able to fly very close )
2) Range :- Maximum limit of height or distance. Most of the drones available today would have enough range for most applications. But in case you are sure your asset is far away do check with the vendor.
3) Operation time :- Ask how much time would be needed for inspecting a single asset. Try to maximize the usage of drone by asking the service provider to carry extra batteries to maximize the data collected in 1 day.
4)Analytics:- Analysis that would be required on the imagery like extracting details , assessing damages , generating reports. Almost always the service provider may throw some confusing words with some AI and Machine learning in it. Strictly speaking it doesn't matter if the service provider is using AI or doing it manually as long as the assessment is within your time bounds and the costing is same. Don't just choose a vendor based on what he says check the reports personally to be sure of what you would get finally.
5)Costing :- Depending upon the kind of drone the service provider brings the pricing would vary. Make a note of quoted value from different vendors with the similar drone. Also just don't cut short on Analytics ,a drone data in the form of just imagery is of no use. Either make provisions in-house or make sure the service provider does the necessary pre processing so that you get concise reports.
SURVEYING:-
Drones seem to have taken surveying industry by storm. With the reduction of costs in photogrammetric processing software and access to cloud based processing the industry seems to be blooming. It seems like you don't again have to use the traditional ground based surveying techniques. Is that so?.NO ABOSLUTELY NOT.
Although the photogrammetric surveying technique is fast and relatively accurate. It doesn't solve all your problems. Naming a few like you don't get terrain information under the tree , terrain data in grasslands , terrain data in dense forests.
Again let's get back to the questions one should ask before opting for such survey.
1) Is your land parcel huge ?
2) Do you need the surveying to be done at a fast pace ?
3) Is high resolution ortho photo must for your project ?
4) Are you flexible with the changing accuracies over the entire parcel ? [yes it's true ! the data would be more accurate near GCPS ]
5) Is your accuracy requirement between 10 - 20 cms ( Elevation )and not less [ A lot of vendors would be happy to give you accuracy of 1 - 2 cm ( Elevation ) be careful with such claims ; if the accuracy is of utmost importance for your project do cross check carefully ]
6) Do you need a dense point data for cut fill or volume calculations ?
If all or few of your answers are yes then you can think of using drones for your project. Some key metrics to take a note of
1) Ground Sampling Distance :- Well this is the most important metric. This is what defines the resolution and indirectly the accuracy of your data. In simple terms it's the length or breadth of the ground that is covered in one pixel. The smaller the GSD the better the quality of data. But that just doesn't mean having very low GSD is a way to go. Defining a GSD would indirectly define the time required for surveying and processing. To get a small GSD ( clear picture ) the drone would have to fly low and have to do many passes over the site thus increasing the time of acquisition and more number if images would lead to more time being consumed for processing. Ideally a GSD of 2-3 cm would give you accuracy of elevation in the range of 10-15 cm.
2) GCP ( Ground Control Points ) :- As stated earlier accuracy depends on the GSD and Control points laid on the ground. Control points are nothing but markers on ground whose readings have been taken using Total Station or DGPS. Around 2-5 points per square kilometer are sufficient for most cases .These points will be used by the Photogrammetric processing software to correct the model errors. This is a very critical step. Chances are the final data you receive may be incorrect only due to incorrect readings of GCP OR using very few of them.
There is also a new module that people offer with survey package called as PPK .It's basically a GPS placed on the drone whose data would later be corrected using the data gathered from the ground static GPS. But that doesn't mean you would not need any GCPs you would still need a few of them. Also be very careful while using PPK and do necessary cross checks on the ground. Also the Static GCP should be placed on a know point for the data to match with surrounding bench mark elevation.
3) Side Lap And Over Lap between photos :- Although this part is usually a headache of the vendor. But a poor data set with low side lap and overlap would lead to highly inaccurate data being generated. General rule of thumb is to have side lap greater than 60 % and overlap greater than 80 %.
4) Camera Quality :- A better camera with better sensor size would lead to a better outcome. Especially if you are planning to use the Orthophoto for feature extraction and other purposes. Always check which drone/camera the vendor is using.
5) Flight Time / Range :- Make sure you know the amount of time the vendor would take to cover your project. Ideally a drone could easily cover 5-10sqkm of area OR 10-15 KM of linear survey in a day. You could gather way more depending upon the type of drone and the GSD expected.
6) Processing Time :- Always make sure that you ask for the time taken for processing. It could run into days depending upon the images and GSD. Also photogrammetric processing do generate error some time. Make sure you personally verify the outputs with the data gathered on ground.
7) DSM / DTM :- The key point to note while dealing with drone survey is that you get Digital Surface Model. SO basically your elevations value represent the surface of a tree or a structure and not ground beneath. In most of the cases people use automatic workflow to remove structures and generate the terrain Model. Again this is an approximation and almost always there would be some error that is generated due to this. So be very clear about your requirements in terms of how the DSM to DTM would affect your calculations.
8) Costing :- The pricing is generally defined by the unit area or unit length along with the GSD requirements. Plus the cost of laying and recording Ground Control Point. Don't just blindly go with the vendor who quotes less. Do get into the details like the no of GCPs laid , the equipment that would be used , processing software being used , the work flow that would be followed. Always ask for missions before hand to check if the vendor know what he is going to do on field.
Apart from the above metrics nothing beats the educated and knowledgeable service provider. No matter how powerful a tool you have a poorly educated vendor would not be able to deliver that excellent outcome you were expecting by using drones.
Be very careful of vendors that charge you extremely low. They almost always have very limited experience in usage of drones. Chances are they are going to cut short on a lot of things. This could lead to a bigger problem if your designs or calculations are based on incorrect information.
VIDEO MONITORING:-
Lastly it's the plain old simple video recording of the project. Nothing fancy here if your project can be shown better in an aerial photo/video and the service cost is justifiable go for it.
points to be noted
1) Resolution :- It could be HD , Full HD or 4K. Most dji drones offer 4K resolution. Higher the better.
2) Annotations :- Overlay critical information on the video. It could be location , asset , metrics etc.
4) Good Pilot :- A good pilot is must unless you are planning to capture video using Autonomous Navigation.
This service is usually very cheaply available. Do cross check between vendors before finalizing anyone.
Hopefully I was able to give some clarity with regards to usage of drones in your domain. In case you are still uncertain whether drones are helpful in your business you can reach me personally. I would be happy to help you out.
Thank you for reading.
