What data is generated by flying a mapping mission? Anything special or just a collection of geotagged still images? Apologies for my ignorance on this, how is what is generated imported to something a professional land surveyor could use?
It's the same as most other survey apps (Mission Planner, Pix4D etc. etc.). The Mapping mission consists of an area you want to survey and your settings for what resolution of images/how high you want to fly and how much overlap between images. That's the "Input" on the ST-16S. The "Output" is indeed a set of geotagged images which can then be processed by any of the standard survey tools - Agisoft, Pix4D etc.
The processing takes a while - an hour at the least (and overnight runs aren't uncommon), and if you're using a desktop app, you need a decent PC to run it. When the images have been processed you can end up with:
a) An orthomosaic - that is a single, stitched photo that is stitched and warped so that all vertical objects remain vertical. It can be overlaid on Google Maps or other survey data. For instance: Crucible The original image for this survey covers about 12 acres and is around 283 megapixels.
b) A point cloud - that is a few million 3D points that make up the surface of the area you surveyed. This can allow you to measure obects and volumes within the surveyed area. It's not easy to share online, but an example of an online viewer with some sample datasets is here: plas.io
c) A 3D textured surface - that is a 3D model using the point cloud and photos combined to give you a physical representation of the area being surveyed. You can view this in a number of different packages, including various online tools. As an example: Crucible Woods by tunauav - 3D model (Note that this is reduced resolution over the normal output - the generated file is a few hundred megabytes).
There are some other options you can play with - such as false colour and extended spectrum photography (used in agricultural surveys) and thermal scans.
For accurate processing you may need to generate a ground control point (GCP) file - which is used to precisely locate the geotagged images so that they produce more accurate maps. Without GCPs the surveys can be a a few inches off, which is less of a problem for some survey types than others. With ground control points, accuracy can be brought down to an inch or two - but getting below that threshold is difficult and expensive. Civil engineers will be disappointed to find you cannot get millimetre accurate models through aerial surveys. Creating a GCP file usually needs an accurate GPS locator, which is used to spot measure a number of reference points (usually specially marked mats) that allow points in the captured photographs to be precisely located.
Very good explanation
With respect to the precision of the models it is possible to obtain millimeter precision, a GSD of less than 1cm can be achieved. .
More good advice, thank you. - RickIt's worth pointing out there is a difference between resolution (the physical distance one pixel in your orthomosaic covers) and accuracy. Flying lower and using a higher resolution camera increases the detail - and these days you can easily go to 1/2" or 1cm per pixel, which is enough to spot small details in your map.
Accuracy comes from a combination of GPS sampling, lens distortion and stitching artefacts - and can be quite variable. The result is that a straight wall of 100m might measure as 100.5m on the orthomosaic, or appear curved or bent. Though the detail may be high enough to see the mortar between bricks, the accuracy may be far lower. It's this that causes problems for civil engineers, and why you might choose to use GCPs to improve things.
Accuracy comes from a combination of GPS sampling, lens distortion and stitching artefacts - and can be quite variable. The result is that a straight wall of 100m might measure as 100.5m on the orthomosaic, or appear curved or bent.
I will use 4-5 ground control points in various areas of the mapping scene, run my mission with images being geo-tagged with the aircraft gps for 5m+ accuracy then post process. So ill get my ground control point data and post process to gm cm accuracy on the ground control points. Ill then import all the images to Photoscan Pro and basic process, then add the ground control points into the data, and manually optically line them up over 3-4 images, that will then give accuracy to 1cm+/- in xy, and around 5cm z@bluelight.support , do you mean you post processing the Ground control Points, or are you post processing the geotags on the images somehow?
Yes - if you ensure that your ground control points are geo-accurate and match to your data, then when you create your contours they will all match as part of the data set. I only use Agisoft as dont like the workflow in Pix4D and also had support issues with the software.A question from myself if I may.
I need to be able to produce accurate topographical contour drawings as in just the contours in black on white. If I use GCP's for accuracy am I correct that using Pix4D or Agisoft it is possible to produce such a drawing?
Thanks for the info @bluelight.support I am investigating its accuracy and use for our company and I will need to do some real world trials soon and with a bit of luck will get a nice bit of drone work out of it.Yes - if you ensure that your ground control points are geo-accurate and match to your data, then when you create your contours they will all match as part of the data set. I only use Agisoft as dont like the workflow in Pix4D and also had support issues with the software.
Thanks for the info @bluelight.support I am investigating its accuracy and use for our company
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 do all the processing in Photoscan so do the initial processing, add GCP for cm accuracy and go from there - the workflow allows for point clouds, 3d models, orthophotos, contours, measurement volume, etc - no im still using phantom 4 pro as its mechanical shutter. Went from Inspire 1 Pro which was brilliant, to the Inspire 2 which is rubbish, and Phantom, still waiting for the yuneec to be a little more settled and functional before taking the plunge, I like the hex, but would also prefer 2 battery for backup.
Thanks, I will look closer at this when I get home from workIf you are after accuracy you may want to consider something like this
Reach RS+ — Emlid
It is almost $800 but a) it will give you a centimeter accuracy b) you only need one station.
With this RTK you can have just simple DIY tiles as GCPs and you can have as many as you want at almost no cost. However you will need to record coordinates of each of GCPs centers and then correct each tile position in your mapping software.
If you scroll down a bit on the page on the link above there is a picture of how it is done. So you will be doing the same at each GCP and recording each GCP coordinates.
Another option is just get an RTK module (Reach M+ — Emlid) from them and build a station like this yourself, Their RTK module is less than $300 and I believe you should still be able to use their app to connect to it and get all data from it.
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?