Mapping Operation and Post Production of Images
Aerial mapping with a drone. The subject matter will cover the process of, drone operation and post production of images to allow stitching of images into an aerial map.
We shall be looking at coverage areas, sectoring, operational height, focal length, scale calculation, apps, mapping times, mapping software.
We shall be using the DJI Inspire 1 with X3 camera; you will need a minimum of two TB48 batteries per 20 acres, Maps Made Easy Map Pilot App, Maps Made Easy Map Processing Account.
To illustrate how to carry out a mapping survey we shall use a recent example requested by a client to map woodland.
When you receive your first brief to carry out a mapping survey, be prepared to factor in an additional 50% more time until you become more skilled at the work.
This is your standard preparation to deploy a drone. Before you accept the brief is it safe to deploy the drone within the area and what are the risks? Use your usual method as per your Operations Manual. If you are happy with the location and can safely deploy a drone then you can accept the brief.
This is not the operations brief.
Mapping preparation understands the clients remit. Type of mapping survey, map scale (1:5000). area of survey, mapping time (20 acres will take around 20 minutes to map) so work on a ratio of 1:1 (1 acre:1 minute flying time), terrain features, lens to be used, resolution of pictures, focal length of camera, sectoring the area to be surveyed.
Operation height normally used is 100m AGL.
When looking at the brief check for high objects, such as wind farms, high terrain etc, anything that will be above the drone height and within the mapping area.
Remember the drone will be on auto. I found that it is also advisable to download the paid terrain app from Maps Made Easy as well. This can be uploaded for the mapping area and will provide the drone with terrain clearance and thus avoid high ground. However it’s up to you as a pilot to always check when on site.
Mapping Made Easy account will be required, Google Maps and Explorer OS for the area to be mapped. Once you have received the brief from the client it’s very advisable to use Google Maps and plot the area then ascertain the square meters or acres. Remember to add a further 50% more time you think it will take.
Programming the survey area using the Maps Made Easy App into the iPad. This has to be carried out with an internet connection. Checking the programmed survey area has been stored and test with simulator. The programmed map will be cached and stored on the iPad, once on site and no available internet connection you will not be able to alter the programme or add further programmes unless you have access to the internet.
Select the area you wish to Map then carefully assign way points around the area (20 Acres) and the app will plot the area; this can be saved on the device. I use iPads and always programme two iPads up with the survey areas with slightly different areas. This has proved invaluable on occasions when I have found the mapping to have not completed correctly.
Maps Made Easy has some in depth instructions with regards to this process.
I would always recommend finding a suitable plot of land with no obstructions and carrying out a small practice mapping survey. At least 5 acres will be required; 10 acres would be preferable for this exercise.
Always assign the drone to either cross longitudinally or laterally. Do not use zig zag as I have found when stitching the images together the programme will miss key images and therefore the mapping will not be complete.
I also advise that you always programme the images to have a 60 to 75% overlap at least.
Aerial Scaling for Mapping
Often you are asked what scale will the aerial photograph be?
A method used to determine the scale of a photo is to find the ratio between the camera’s focal length and the plane’s altitude above the ground being photographed.
On arriving at you assigned site the map or maps can be recalled and it will be uploaded into the drone. Allow a little time for this, at least 4 minutes to upload. Once uploaded the app will ask to start and the drone will begin its mapping sequence by auto take off and climb to the assigned height. The drone will carry out a 360 degree orbit at the assigned height to establish the wind direction. Once this has been done it will fly to the start point and begin the mapping. If battery change is required the drone will return for a battery change then complete the mapping assignment. Once complete the drone will return and land.
Please always check that the drone remains visual at all times and that public or animals will not walk into the takeoff and landing zone. The drone will be on full auto functions including landing.
Creating the Map Survey
By uploading all the images from the survey to Maps Made Easy the stitching process will begin. I find that by copying the images and reducing their size a separate test map can be made. If you are happy then upload the full resolution images. Maps Made Easy usually takes 30 minutes to finalise the stitching process. A notification will arrive and you can view the complete map on line then select your preferred file version to download.
You can also select 3D imaging. However to attain the best results for 3D you really need to take a number of images at three selected altitudes of the same mapping area. Such as 100m, 70m and 30m to produce a 3d imagery of for example woodland.
Another great piece of software is Irfan View which allows you to renumber multiple images or resize multiple images at one time.
I have found by using Maps Made Easy that very comprehensive aerial surveys can be completed. The client however may just want the images only to be used on their own bespoke mapping software.