Alignment Experiments

[MeHoo]

This is awesome, and I will be digesting this all again and making my own tests, although not as well defined as yours I'm sure.  My machine for PScan is a dedicated box with Dual quadcores at ~3Ghz, Two 970GTXs, and a Quadro K4000, with 256GB ram, and two SSDs to store the photos locally instead of my server.. I can do tests where the machine will never be used for anything else as this is a dedicated box 100% for photscanning.  I wouldn't mind more info on exactly how you structured your tests and results so that I can have a great template to do my own on my rig.  I would like to test the hardware end, not just the software settings, and you seem to have a very nice experimental demonstration to use as a benchmark.  Thanks again.

[jphil]

I know this is kind of an old thread, but I've seen it referenced a couple times and was hoping someone might be able to clarify the original post.

Is he saying to set Key Point Limit to 120,000 and Tie Point Limit to 40,000 when running Align Photos, because a dense cloud doesn't benefit much from anything over 40,000 points? And you don't really gain many points with an error less than 0.5 pixels over 120,000 Key Points?

[mradityawan]

I just ran some tests on a few existing images (of varying quality and content) and its seems the relationship between megapixels and maximum number of keypoints is approximately linear.

With 6MP Fujifilm S6500 i got ~35000 keypoints
With 12MP Nikon D90 i got ~70000 keypoints
With 16MP Nikon D7000 i got ~110000 keypoints
With 24MP Sony NEX7 i got ~150000 keypoints
With 36MP Nikon D800 i got ~240000 keypoints
With 50MP Canon 5DSR i got ~320000 keypoints

So the formula is that max no. keypoints ~= megapixels x 6400

i didn't include the fact that one of my nikon d800 images returned 280,000 keypoints as that ruined the graph and contradicted what Marcel posted. also his figure of 180,000 points for a 21MP camera doesn't fit either. i think this may be down to the fact that most of my images are not ideal, particularly with the lower end cameras, so there could be something more complex going on.

Also these were tests on JPG files, so TIFs or similar may give different results.

if you want to run the test on your own images, just make sure the console is visible when you run align images, with key point limit set to 0, and the console will display the number of key points detected in each image early on in the process.

Hey Mr James,
I'm rifki from Indonesia, I have any questions for you about alignment parameters. Someday you have statement that formula to get max no. keypoints ~= megapixels x 6400. How u can get 6400 from formula? It's constant? Can I use ur formula to align process of key point limit and tie point limit?
I'm newbie in agisoft and still studying for it.
Thank's before.

Rifki

[James]

Hi Mr Rifki,

I plotted my findings in Excel as a scatter plot, with number of megapixels of the image in X column, and number of keypoints detected in Y column, and got it to plot a linear trend line passing through the origin (0,0 because no megapixels = no keypoints), and the gradient of the line ('m' in y = mx) was about 6400 ---> keypoints (y) = 6400 * megapixels (x).

It doesn't mean this is a value you should ever use for anything, just that it was the number of keypoints that photoscan would extract from images of a certain resolution, if you don't limit it.

[Vlad]

Original post lost all images, due to picture hosting provider.
So i decided to make a copy of original post, because such valuable information should not lost in time
https://medium.com/@ssh4/alignment-experiments-from-agisoft-forum-by-marcel-19b2c7727d7a