We (www.gmxconsulting.co.uk) are developing a large-scale agriculture project in Nigeria (5,000ha) and started to use drones to survey and map topography.
The intention was then to use the Digital Elevation Model for irrigation planning and design. However, when we post processed the images we got very large x y z errors - please see the photos below.
1. Could anyone tell us where we have done wrong? Can we correct NOW (after the aerial survey)?
2. Also we look to outsource the drone surveying and post processing for our projects in Africa - Anyone interested please let us know.
Here are some more details:
Platform: E384
AGL: 120 - 180m
Overlap: Front 60% Side 60%
GCPs: No
Flight time: <60 mins
Cameras: Canon S110 RGB and NGB
Number of photos: 300-400
Photo taken out before processing: None
Software: Photoscan
Many thanks in advance!
Replies
There is a way for you to improve your UAV produced photomap precision significantly (cm accuracy level) without the need to use any GCP. Check this link out. Or, you may try this for RTK GPS on your plane.
Thank you. We spoke to Walter before regarding our project. Our timing was too tight so we had to do it ourselves. Best. Quan
I agree with the above comments. You need accurate ground control points if you are looking to produce an accurate model. The number and positioning and accuracy of the GCPs is also important and depends on the topography. This is something that comes with experience. Another aspect that hasn't been mentioned is image overlap. For consistent results, I would recommend a forward overlap of at least 80% and side lap of 75%. With a simple terrain you could probably get away with less, but rather safe than sorry. Their are other factors such as weather conditions, flying speed, camera settings that all come with experience.
Having said that, you could probably get reasonable results from your images just by adding 5 or 6 well positioned ground control points.
Let me know if you need any more info. You're welcome to contact me any time at ian@aerovision-sa.com.
We are an aerial surveying and mapping company based in South Africa.
Regards,
Ian Freemantle
Hi Ian,
Many thanks for your comments. Thought I covered some of the points you raised in my previous response. I am on quan.le@gmx.com and we are looking for partners to outsource the flying and processing part if possible. Best. Quan
Hi Gareth
Looks like GCPs are the way to go. As mentioned in one of my responses, we couldn't exactly established 'where we are in the world'. We were working in a remote location so we had to make do with some estimated datum.
My question for you is that, given the accuracy that you get can you actually replace traditional survey (e.g. with total stations) with drone topo surveys? In that case could you produce 1:500 map accurately?
Right now it takes 1 surveyor in our team 1 month to cover about 1000ha to produce a lower resolution map. So if drones can replace this cost-effectively the then our irrigation planning and design work in Africa will be transformed.
In that case we of course still need someone on the ground 'to have a feel for the place' and do some geological survey. But our field work would be cut short and time instead be spent in the office to do the design.
Please do send some further info to quan.le@gmx.com. Thanks
Hi Quan Le,
We are a Survey Company located at Paarl in South Africa and have been using UAV's for the last 3 years to do Aerial Topographical Surveys throughout Southern Africa. It has been an expensive "learning curve" through which we had to go to iron out mistakes and get a working "Work Flow" in place.
At this stage GCP are necessary to have an accurate survey of the area that has been flown, but we are looking at possible solutions where GCP are not necessary. The method entails having a Base Station on the ground and then a Rover on your Plane.
You could correct the Survey by visiting the area again and fixing (X, Y & Z) features over the area that are visible on your Photos.
We would be very interested in doing the Surveys for you and we can be contacted at info@aerialpix.co.za.
Regards
Michael
Dear Michael
That is exactly what we are planning to do. We still have a team on the ground. Instead of re-flying we will take the xyz at visible landmarks to see if the accuracy improves. We still have a lot of area to cover so in future surveys we will use GCPs.
We are agriculture developer and manager, not an UAV survey company. Our interests in UAVs are in the end-user applications - produce topographic map for irrigation planning; taking stock of the farm/plantations; count trees and animals; monitor crop growth (e.g nutrient or water deficiencies) and the specific management actions to be taken from these.
We will retain the interpretation of data, growing prescriptions in house and look to outsource the data acquisition (flying) and post- processing when we can.
Right now UAV uses will need to make our work cheaper and faster - that is the key consideration.
For UAV surveys the key outputs we need for irrigation planning and design are:
- contour map with x y z at scale of 1:500
- orthophoto
As we are designing, developing and managing agriculture projects in Africa we would like to partner with UAV surveyor, companies or individuals. Our projects are generally >1000 ha.
Please could you send a proposal and some example of your work to quan.le@gmx.com ?
Thank you.
pls email me directly.
darius
manta103g@gmail.com
pls email me directly.
darius
manta103g@gmail.com
Hi Quan Le,
First of all, it looks like worse precision areas are located in the border of your mission region, probably where the plane turns and where you are taking (and afterwards processing) no nadir images (ie, not zenital, with large camera location error). In those cases you can exclude these images from your analysis in Photoscan. That should improve overall precision of your models.
If that region is important for you, you must extend your missión farther next time to keep that area in level flight (ie, make the turns outside there). You can also increase image overlapping to 70 or 80% in at least one side. If your camera is fast enought that should not increase your flight time very much (you can also flight slightly slowly, if possible).
Another way to correct that is using some GCPs at easily recognized items of your images. Even with a conventional GPS you will improve your models (at least, its geographical position).
Hope that helps you.
Regards
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