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You can use the UGCS application with which your h520 will do the mission taking into account the relative altitude of the terrain.
I think it needs to be pointed out that you should take these claims of cm accuracies with a grain of salt. While you may get cm relative accuracy to your known point using RTK, your map can only be ~half as accurate as your known point. I've pointed this out before. You may expect accuracies of a quarter of the vertical accuracy of your known point. These are the standards set out by the ASPRS.
If you start doing mapping and photogrammetry work you had best know these things and not oversell, especially if one of your clients ends up taking you to court. It should also be noted, in the States at least, that you may be running afoul of certain state laws for surveying, mapping, and photogrammetry if you are performing these services without a license. Something to think about.
Indeed, and there is an important distinction between resolution (number of pixels per cm/inch of ground) and accuracy (where the stitched image appears to place each physical feature). Mapping is a mathematically complex process with a lot of parameters - but the quick online apps make it appear that anyone can just fly a drone and produce an 'accurate map'.
I answered on the other thread, but I'll respond here as well - you want the images to be at different distances from the ground so that the stitching software can accurately calculate the actual terrain being measured. A proper mapping application is not simply joining photos together to make a large photo - it uses the different speeds that things move past the camera (parallax effect) to calculate the actual height of the objects being photographed. That generates a detailed surface model that is used to 'warp' the photos so that vertical things appear vertical in all parts of the image. In ideal circumstances this should eliminate all the effects of taking photos at close range with a wide angle lens, and produce a final image that is as though it were taken from infinitely far away (no distortion).
I appreciate what you are saying, but I am investigating for a company I work for initially to understand what we may be able to achieve for drone surveying and inspection. I will hopefully be trialing aerial mapping for them soon and need to find out as much info as I can. The imagery and topo surveys will be handed to the CAD guys to decide if they are accurate enough for them to use and produce drawings suitable for setting out of certain things, we are not talking millimeters here. I will not be exposing myself to any liabilities.
I never considered I would simply be "throwing some pictures into DroneDeploy"
True, but then some of the blame should lie with those selling the products and "how to start a drone business" videos. It is the same with all new tech as far as I can see.Understood, and that comment is not necessarily directed towards you... I was speaking more generally about that I see in the field. People try to sell the service without knowing the first thing about it and I feel like that is bad for our industry as a whole.
You can use the UGCS application with which your h520 will do the mission taking into account the relative altitude of the terrain.
I have a home built quad that carries a Sony a6300 APSC camera that will follow terrain in missions to maintain a given AGL. But uses a Pixhawk 2.1 flight controller running Arducopter.Thanks interesting, I was asking in another thread how mapping copes with uneven terrain like a hillside, if the mission is all photographed at the same altitude then all images will be at different distances from the ground, so how does this all stitch together accurately, or can the phantom maintain a set distance above ground level?
I appreciate what you are saying, but I am investigating for a company I work for initially to understand what we may be able to achieve for drone surveying and inspection. I will hopefully be trialing aerial mapping for them soon and need to find out as much info as I can. The imagery and topo surveys will be handed to the CAD guys to decide if they are accurate enough for them to use and produce drawings suitable for setting out of certain things, we are not talking millimeters here. I will not be exposing myself to any liabilities.
I never considered I would simply be "throwing some pictures into DroneDeploy"
Would you care to expand on the build? A home build is on my long list of projects to consider, currently thinking of a Tart 960 with Pixhawk 2 cubeI have a home built quad that carries a Sony a6300 APSC camera that will follow terrain in missions to maintain a given AGL. But uses a Pixhawk 2.1 flight controller running Arducopter.
Would you care to expand on the build? A home build is on my long list of projects to consider, currently thinking of a Tart 960 with Pixhawk 2 cube
It a custom using 25mm CF tubes.Cool, what frame is that built on?
There are many build threads out there for PH builds. Setting up the bird to fly has also become easier with more automated tools in arducopter, so I wouldn't be too concerned about that. The main thing to do first is determine payload and All Up Weight (AUW). Then obtain the necessary hardware to match that weight.What wheelbase? I do find the idea slightly daunting, not so much the design and build but the setting up and programming and wonder if I could cope. I was thinking of building a F550 from a kit but I would have no use for it once finished or if I should just jump in at the deep end, I wish there was a bit more reading material on the subject
Gents,
This subject is full of so much misinformation.
The stitching software we use (Pix4D agisoft etc) are matched by points across many photographs before a GCP is encountered - you have no way of confirming how accurate this process is.
Your photogrammetry software may be stating 15-20mm accuracy on the GCP but the GCP then selves are picked out and have a pixel distortion depending on the GSD- they also are usually GNSS measured so there is another 20-30mm.
So the BEST you will be getting is 50mm!! Then it will distort between so depending on the light and shadows, Overlap GSD etc you can not guarantee a map precision!!
Unless you have GCP in every image!!!
I have carried out many experiments comparing to laser scan / total station and GPS surveys.. depending on GCP placement the level accuracy varies immensely - I have seen level errors of up to 3 meters!!! The best I have seen is +-75mm and some areas towards the edges were double this.
A huge amount of experience an knowledge is required in geospatial methods and techniques before you can begin to be confident with the tolerances.
I do not feel that this technology is to be used for Topographical survey - it is simply not accurate enough. But as an additional deliverable (2D ortho overlay) or for volumetric survey it has advantages..
Arruntus these are all tests done by the software vendors.I don't agree with you on this. When the images are put together, hundreds of thousands of points are compared, which makes them perfectly linked (keypoints). Another thing is the model that is not correctly georeferenced. It may be tilted, not having the correct scale, etc. This is where the GPC's or RTK georeferencing comes in.
Since the model is geometrically correct, matching it to reality depends on the accuracy of the reference points provided to the photogrammetry program. I have seen comparisons between photogrammetric models, models with total station and using GPC's and the variation between the control points of the different techniques only in very few cases reached 10mm. I have found several studies that show what I am saying.
For example:
How does photogrammetry measure up? A comparison - Pix4D
Do RTK/PPK drones give you better results than using GCPs? - Pix4D
These two videos are in Spanish, they are worth watching:
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