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Author Topic: aerial photography?  (Read 22607 times)

sigma

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aerial photography?
« on: May 01, 2012, 02:26:10 AM »
I am considering evaluating Photoscan Pro for an architectural project.
I would like to generate a 3D model of a valley using an array of high res aerial 2D photos. The valley is approx 1 km wide by 2 km long. I want the output model to give me a resolution of 5 meters or better so that it can be imported in a CAD application and worked on by architects.
 
1. Is this possible with Photoscan Pro?
2. how do you recommend I take pictures to achieve that resolution (how many pictures, at what angle, etc)?
3. At what altitude should the photos be taken, ideally?
4. Will a 7MP camera be sufficient for this or should I use a better resolution?
5. Should I use the optical zoom to achieve better results?
6. How can I determine the ideal number of pictures to be taken?
 
Thanks!

fpbv

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Re: aerial photography?
« Reply #1 on: May 01, 2012, 05:54:10 AM »
Sigma

This needs a proper mapping engineering planning to do this, to calculate the strips, the overlapping between photos, etc.
To do this you should tell which camera do you have available and which lens.
If you want I can help you on this, I am a cartographer engineer with 14 years experience in aerial photogrammetric/GIS projects.

tezen

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Re: aerial photography?
« Reply #2 on: May 01, 2012, 01:12:03 PM »
Hello sigma!

Maybe you even don?t need the Pro-version because of your wanted size.

1km*2km at 5m resolution will be a 200px*400px (=80000px) heightmap (really small). 1km*2km at 1m resolution should be possible (1000px*2000px = 2000000px) heightmap. And the object could have an 10000px*20000px texturemap which means one pixel for every 10cm?. This should be enough for your project I think. You could generate 3D-objects with 5000000 Polys and much more texture-size - it depends on your computer.

A 7MP-Cam could be enough for this if you shot 100 Photos or more. More Photos means more quality and more MegaPixels (without noise) means more accuracy. For heightmaps it?s good to use the same altitude and same angle looking to the ground. Just try-out PhotoScanStandard with your 7MP-Cam and photograph some old buildings or walls etc. - you will be fascinated by the precision.

A better Cam will give you better results. Take a look at the new SonyAlpha 57 (16MP) or SonyAlpha 65 (24MP with builtin-GPS for use in the PhotoScanPro).

Optical zoom gives you better results (less lens-distortion) if you don?t want to undistort photos for fast creating 3D-Models (maybe of some trees or stones in the valley) . But you?ve not to change the zooming until the session ends.

If I were you I would contact fpbv!

All the best.

Greetings
tezen

sigma

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Re: aerial photography?
« Reply #3 on: May 01, 2012, 05:52:59 PM »
Thanks so much for the replies!
Indeed, it makes a lot of sense to try it out first.
So here's what I will do: First, today I will take pictures of another geagraphical feature (a smaller landscape) and try to import them in PS. Then, provided the results are encouraging, I will plan my visit to the valley with the help of fpbv (thanks for the offer!), considering the lens, height, etc.

My alternatives at this point are to hire a lidar survey (~ $30,000 USD) or a field visit with a topographer (3 ~4 weeks to take physical measurements with a handheld GPS). So I would much rather make this approach work!

10 cm resolution would be overkill, but if the data is there, I'll certainly use it. 1m should be more than adequate. Do you think that 5,000,000 polygons will be enough to map an area of 2,000,000 pixels, considering that there are large variations in the height of the features on the land (peaks more than 1,000 meters higher than the center valley) ?

Oli63

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Re: aerial photography?
« Reply #4 on: May 01, 2012, 06:52:59 PM »
Let me make you an offer:
we will do the whole work for you for 15000 $ and you will get 2 cm ground resolution.

Oliver
GeoSpy Aerial Imaging & Mapping GmbH
www.geospy.at

tezen

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Re: aerial photography?
« Reply #5 on: May 01, 2012, 09:38:36 PM »
Hello Sigma!

If my client would spent me so much dollars (and time) for this project I would do this:

Buying a big quadrocopter (~10000$) for a high-quality remote-controlable-cam & gps-system (like Sony Alpha65 for ~1500$) for taking thousands of photos from different perspectives of each valley-wall and the valley itself (Btw for your try-outs: Cloudy diffuse sunlight at the middle of the day is the best and there shouldn?t be winds for natural photography). With a nice PC (~5000$) there will be good PhotoScan-results over night with more than ten millions of polygons. Which means for roundabout 5km? (2km? ground, 3km? hills and trees) more than two polygons per m?. Thats enough if you think about flat areas (with less polygons) and a higher resolution texture(s) on top of it. You could calculate even more polygons by changing the setting or by splitting the ground, hills and some interesting parts (like rocks) into "chunks". For more releastic results I would built up a low-resolution 3D-background around the valley.

Of course you?ve to retopologize the high-resolution-results for better use in other rendering-software. Afterwards you?ve big equipment for future projects. But it could be hard work.

2cm? ground-resolution means 12500MegaPixel-Texture, 12500 Million Polygons and even more?!

Greetings
tezen

sigma

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Re: aerial photography?
« Reply #6 on: May 02, 2012, 07:17:14 AM »
Oliver: thanks for the offer, but I think I'll do this myself... :)

Tezen: Indeed, the price is ridiculously high, hence the reason I'm looking for alternatives. But I like your wish list: the quadrocopter sounds like a very cool gadget!

Went out and took pictures of a rock formation today. The feature is approx 500 meters high, and 700 meters wide. I used a cheap 8MP 'pocket' camera at full resolution. Only took 17 pictures, from the road, about 700m away. Sun was setting, so not all pictures are very clear, which somewhat affected the output model.
Everything processed very well, and PS generated almost 2 million polys (ultra high quality, smooth geometry). I need to go through some of the tutorials to see how things can be improved, but so far, I'm very pleased with the potential.

How can I assess the resolution of the generated model? The software tells me the area is 1.2 m^2. I'm guessing there's a way with GCP to correct that, but I won't do this for this test model. But is there a way to determine the height of one polygon with respect to the overall height of the generated model?

Thanks again!

tezen

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Re: aerial photography?
« Reply #7 on: May 02, 2012, 04:27:26 PM »
Hello Sigma!

Use a good DSLR-cam instead of a 7mp-pocket-camera the results will be much better because of a bigger&better sensor. Take a look at this picture for all those different types of cam-sensors and you know what I mean: http://de.wikipedia.org/w/index.php?title=Datei:Sensorformate.svg&filetimestamp=20081203074952 . Just borrow one DLSR-cam from your friends or family and compare the results.

If you own a good HD-Cam: Just take a walk around an object and cut the recorded video into roundabout 100 (sequenced) pictures. It works - not really good but it works if you want to scan a high number of objects in short time. Take a look at another software (not released yet) which shows this technique: http://www.vi3dim.com/ . For sure PhotoScan will give you better results if you use 600 (!) HD-cam-pix.

Ask Alexey about your scale-question. Don?t know...

Greetings
tezen

sigma

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Re: aerial photography?
« Reply #8 on: May 02, 2012, 07:21:49 PM »
Hi tezen!
yes, for the actual photo shoot, I will be using a Canon EOS7D with a Canon 18-55 mm lens. That should improve the results significantly.

fpbv,
if your offer still stands, I would very much appreciate hints/tips on how to approach this project as professionally as possible. Although I have a decent camera, the one I have attached to a UAV is of very poor quality.
My initial thought was to take pictures of the periferal mountains from the ground and take pictures of the ground from the mountains on the side. This way I would attempt to get shots that are as close as possible to orthogonal to the surface. I will also try to get 70%+ overlap between shots to make it as easy as possible for the software to stitch the tiles. If that doesn't produce good results, I can use the UAV, but the quality of the photos is barely in t eh2MP range so quality will suffer tremendously.

Anything else you can recommend? Optimal distance from the ground, camera settings, etc?
Thanks!

James

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Re: aerial photography?
« Reply #9 on: May 02, 2012, 07:27:57 PM »
If you own a good HD-Cam: Just take a walk around an object and cut the recorded video into roundabout 100 (sequenced) pictures. It works - not really good but it works if you want to scan a high number of objects in short time. Take a look at another software (not released yet) which shows this technique: http://www.vi3dim.com/ . For sure PhotoScan will give you better results if you use 600 (!) HD-cam-pix

This can work quite well as a way to quickly generate alot of images. I use ffmpeg http://ffmpeg.org and the following command to split into still images:

Code: [Select]
ffmpeg -i input.avi -r 1 -s 1920x1080 -f image2 frame_%04d.jpg
Thought I'd share as it took me a while to figure it out.

input.avi =: movie file - doesn't need to be avi though
-r 1 = rate i.e. 1 image per second
-s 1920x1080 = dimensions of output images

fpbv

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Re: aerial photography?
« Reply #10 on: May 02, 2012, 08:11:25 PM »
Hi tezen!
yes, for the actual photo shoot, I will be using a Canon EOS7D with a Canon 18-55 mm lens. That should improve the results significantly.

fpbv,
if your offer still stands, I would very much appreciate hints/tips on how to approach this project as professionally as possible. Although I have a decent camera, the one I have attached to a UAV is of very poor quality.
My initial thought was to take pictures of the periferal mountains from the ground and take pictures of the ground from the mountains on the side. This way I would attempt to get shots that are as close as possible to orthogonal to the surface. I will also try to get 70%+ overlap between shots to make it as easy as possible for the software to stitch the tiles. If that doesn't produce good results, I can use the UAV, but the quality of the photos is barely in t eh2MP range so quality will suffer tremendously.

Anything else you can recommend? Optimal distance from the ground, camera settings, etc?
Thanks!

Sigma

This camera that you are using is good enough to to the job.
The main concern is the lens, this zoom lens for aerial has some problems, you should have a fixed lens to do, something with 24 or 35 mm lens.
Regarding ground sample distance - GSD - you should see how much do you need: 1 meter, 20 cm, 5 cm, etc.
When you decide how much this will fit to you so you gonna calculate how the optimal distance from the ground and how many strips.
About the 70% longitudinal overlap is ideal to do this, and in addition to 30% or even 40% lateral overlap between strips, you will have a very very good terrain modeling.
In other way you can fly shooting obliqual imagery but you should take care to no have too much skyline.
I can tell you, both ways you will save money and time. If your UAV could carry a point-shoot camera with 16 megapixel so you could have a very good results to.
Don?t try to use 2 mp, you will suffer a lot, I did this with a celular phone but it didn?t work well.
So, just tell us which plataform you want to use: plane or helicopter?

sigma

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Re: aerial photography?
« Reply #11 on: May 02, 2012, 09:32:06 PM »
I can try to find a lightweight 16MP camera and attach it to a plane (UAV). It will take time to get the equipment and assemble it and test it, so I would much rather not go that route if I can avoid it.

As described earlier, the site is a valley surrounded with high mountains (think of it as a bowl, more or less). So, I think I will climb up the mountains and take pictures, hundreds of pictures, from the top of the mountains around the site. I will try to capture a little bit more than half of the bottom section which, as I turn around the 'bowl' should give the software some overlap between all tiles, and capture the site with an as close to possible aerial perspective. I will also get a GPS device to record the exact location of each picture.

Then I could repeat with the sequence from the bottom of the bowl, looking up towards to top of the mountains to help with capturing the mountain tops.

Will the software be capable of 'merging' both set of photos/3D models? Any special processing required to do that?

Also, since this cannot happen very quickly, the sun will change position during the photo shoot. Will this have a significant impact on the results?

thanks again for any insight!

Wishgranter

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Re: aerial photography?
« Reply #12 on: May 02, 2012, 10:22:21 PM »
Best way is to sit in airplane with a good camera, give instructions to pilot WHAT you go shooting.

BUT Oli63 give you a reasonable price because you need a few "tricks" or better be handy with all this and he can teach you a lot of things for your next work like this....

Afther more than year of day-to-day use can say, i know the software good, and it was not my first one..

Personaly if you have budget use use its services and spare few bucks for equipment that you will use later. if done profesionaly the output can shock your clients= more work for you...... that is what im done and its bring me more work....

Sound reasonable ??

Think on that you must climb a lot, take equipment, and later you will find that is not what you wanted.

In what country you live - need to shoot ?
----------------
www.mhb.sk

fpbv

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Re: aerial photography?
« Reply #13 on: May 02, 2012, 11:14:05 PM »
Wishgranter said it all.
The best to do this is to use a airplane.
If you want to I did a similiar valley recently, so I can send you a sample.

tezen

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Re: aerial photography?
« Reply #14 on: May 03, 2012, 05:19:17 PM »
Hello!
I just checked the prices for Quattro- and Hexacopters which are able to carry a 1kg-Cam and for my surprise the prices are between 500$-1000€. Just google for "Gaui copter" or "DJI copter". But depending on the land you?re living in there are a lot of laws and rules. F. E. n Austria it?s relative strictly forbidden to use an air-vehicle with a built-in cam. In my country (germany) you need a special insurance, for commercial use even some licences and so one...
Greetings
tezen