I need your help as the last two weeks of drone imagery capture and RC modelling have produced so many variations and other issues that I am pulling my hair out…I can’t figure out a few things.
I have a couple of test subjects, both buildings near by, and I have had some reasonably good end products but many more that are less than satisfactory.
I am looking for some insight on several levels. For example how much does altitude affect the quality of a model. I have flown at 90ft, 60ft, 50ft and on one building as low as 20ft for nadir imagery but I am unclear what I need to fly at to maintain consistency with future models.
The oblique imagery is another area of concern. I have taken -45d images at several altitudes and generally add two altitudes to my inputs…but do I need to?
My biggest issue is when I try and add facade images, e.g. 0 degrees or face on images. These seem to confuse RC and immediatley break my models by shifting walls to the wrong location…even if I add multiple control points.
Here is a good example of an ‘almost model’ on Sketchfab. Today I flew a whole new mission but remembered to take multiple overlapping facade images pointing up at the overhangs in the shed roof…but as soon as I add these to the pot the model breaks with ghosting points (parts of the roof move) and some walls move into the shed.
Anyone able to mentor me in the image taking area of photogrammetry will be much appreciated. And if the errors are how I am using RC I am more than happy to be educated.
Hello @PBB1956
The first issue there could be the used drone and its GPS precision. As it seems that you are flighting quite low and close to the buildings, the precision could be also low and this can influence the alignment.
The effect of altitude basically influences of the resulted model precision and resolution. As from the higher altitude, the detail of the model is lower and also the precision.
Oblique images are helping for the models to get better height detail, as you are adding also images, which are looking at the model differently.
These posts can be also helpful:
Thanks for the insight and the video links. I had seen both before but I just viewed them again in case I missed something.
What I would like to understand most is why some images cause a 3D model to ‘break’. For example after taking a series of nadir (-90) and oblique (-45 and -60) images with the drone I then took a series of image of each of the facades or sides of the building (drone’s camera pointing straight at the facade) - expecting these to improve any holes in the model and create the area under the overhanging roof but when I add these to the inputs and align them the model gets much worse - a wall can move 3-4 feet into the building together with parts of the roof.
The other area I need to get a grip on is producing consistent models and I am wondering if I always set altitudes the same for all flights will that give me the same results each time?
Is it possible that you can get too close to a building? SHould all images always been taken at a set distance, for example maximum closeness of 10ft or 15ft?
Hi Paul,
the first thing what could break such model could be a wrong alignment. As I mentioned, drone’s GPS is not so precise and when it is close to the building, it could be even less precise. Is this also happening when you try to process the images without the georeferenced information?
The other problem could be the big angle difference between the nadir, oblique and façade images. In general, the difference shouldn’t be bigger than 15 degrees.
Regarding the consistency, to get the almost same model quality, you should take images from the same distance and use the same image overlap. So, it is not about altitude only, but about the distance to the captured object.
You can go as close as it is possible to focus. But then you will need to use more images to cover the whole object.
I think your comment “big angle difference between the nadir, oblique and façade images” has explained my biggest issue!
I have taken nadir at -90, obliques at -45 and -60 but the facade images were head on, so 0 degrees, therefore way more than the 15 degrees you suggest. So the next drone mission will be to bring all angles to within the 15 degrees difference and maintain the same distances for all flight paths.
I’ll get back to you as soon as I can. And thanks again. Good to have a font of all knowledge to hand!
