I’m running a small drone survey business and getting in to the survey industry.
We are working for water management department on canal project. They are building a Dam in the area which will distribute water for irrigation purpose in surrounding villages through canals. The area of interest is 3400Ha or 34 Km square. For covering the area we used Phantom 4 drones and did ~102 flights all over the area. This area has elevation difference arond 50 meter. So i did flights from different areas of different elevation.
My client need 0.5 meter contour map of the area.
I divided the compete area in to sub areas of 100Ha each. So total 34 sub parts. Each flight has following details-
75m height AGL
70% frontlap and 60% sidelap
4000X3000 pixel images
I got around 1400 (7GB) images in a patch of 100Ha covered with single drone using ~3 batteries.
Now when i process these images i need to do it one by one sub part (100Ha area)
Here is the tricky part-
If keep contour base 0 in each map than because i flew from varying elevation the contour line will not match while merging all contour maps.
My client want the Dam base as 0 and need 0.5 meter elevation contour line respective to that. How it can be done?
I observed DTM doesn’t remove human build structure like houses, which create noise in the contour map. How can i get rid of that? Mostly of the survey area is crop field having small villages.
Your project sounds very interesting. Due to the large size of your project (so many flights and sub projects), I believe you’ll need to establish Ground Control Points (GCPs) across your area of interest. There are a number of support articles on the Pix4D site that can help, a great start is Using GCPs
About your DTM for contourn lines, you should edit your points cloud and classiffy those points you dont want in your DTM under DISABLED. The run again process 3. That way you will have a better DTM and contourn lines just from you ground and road surfaces.
Did you all ever find out the best workflow for your project? I too have mapped a very large area and had to do sub-projects. I also had differences in starting altitudes so would like to know the best method of establishing the contour baseline. Regarding GCPs. I captured points using a Trimble Geo XH unit and used WGS84 (Lat/Lon) for my horizontal and HAE (Height Above Ellipsoid WGS84) for vertical. I did not see the Geoid options offered in Pix4d in the Trimble unit so thought of capturing HAE and then converting using Pix4d. I usually set images coordinates to defaults. I set the GCP coordinates to wgs84 and Height Above Ellipsoid at 0 meters. Finally,the output is selected at wgs84 (UTM zone 10n),Geoid egm96. Does this set-up look okay to make sure datums for both images, gcps, and outputs are aligned? Thank you for any help.
I have not done a project with that many flights - however I have done projects with our eBee that have 4 or 5 flights that I need to merge. What i have done in the past is complete the initial processing for each sub project - then I add the GCPs available for each sub project and then reoptimize them. Your flying altitude should not matter if you are using GCPs or MTPs to tell the software matching points.
You should then be able to then merge each of the sub projects together - you may need to define some MTPs to help the software match along the perimeter of each sub flight.
Now I would think if you wanted all the elevations related to 0 - the top of the dam - I would determine the true elevation of the top of the dam - then adjust each GCPs elevation according to the difference and set the vertical coordinate system to arbitrary. IE if 375=0, then all GCP elevations are reduced by 375
“I observed DTM doesn’t remove human build structure like houses, which create noise in the contour map. How can i get rid of that? Mostly of the survey area is crop field having small villages.” - use the Pix4d clipping tool to remove your noise from the point cloud- then create a polyface surface over that area and enable it to be used in the DTM in the properties menu
I’m about to start on a fairly large mapping project documenting a massive field looking for an invasive species of plant. I’ve identified that the lowest I can get away flying is 90ft while still being able to identify the species.
Because the area is so large and I’m looking at roughly 800+ min of flight time and possibly tens of thousands of images, does it make more sense to break up the space into multiple smaller maps or fly the entire field using one map?
I’ve been flying for many years but new to the mapping process so any insight is greatly appreciated.
I’m also going to be need to overlay these maps in something like google earth or similar. Not sure if that changes how I approach the project?
The best suggestion I could give is to have a good overlap between the images and the flights itself. Make sure the image acquisition is consistent and using GCPs is always helpful. For more information, I would suggest going through our support article on Processing Large Datasets.
You can create the google title of your project and overlay it on google earth. For more information, visit How to generate Google Maps Tiles and KML.
If you have large projects I’d recommend to try out Pix4Dmatic. We tested it extensively for up to 10’000 images at 20MP, but we have had feedback for projects up to 16000+ images working and we did not find an upper limit yet.
Advantages:
You won’t have to do the split and merge procedure, but should be able to process all images together. This saves a lot of manual work.
More Geoids and vertical coordinates are supported, see this article.
The processing speed and reliability is much better than in Pix4Dmapper for large projects. Here is a benchmark for illustration.. Note that the DSM and Orthomosaic are also available, the benchmark will be updated soon with these benchmark results too.
*It’s compatible with Pix4Dsurvey for a DTM workflow and CAD ready output.
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