Forum : Advice & Critiques

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Topic: Point Cloud Advice

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Jaleho (Over 1 year ago)
Hello all! I've got a synth of around 1000 photos of an outdoor stone staircase: http://photosynth.net/view.aspx?cid=54265160-87d9-4999-a0d6-68121f622f18
The topography is very complex (lake, side of a hill, curving stairs) and there seems to be some issues with the eastern wall -- if you follow if from the top, it seems to do okay, but if you follow it from the bottom, the altitude goes crazy. It seems to have trouble understanding both are the same wall.

Is there a specific spot I should be taking more shots from to show it how to match them up? I did another 60 shots which all fit in themselves, but seem to get left out of the larger synth.

Thoughts?
jimcseke (Over 1 year ago)
Hello Jaleho,
I have been trying to convince others of a photographic method I have researched and developed. I won't get into specifics, but this does work. My methods have more to do with accuracy and how your camera is orientated than anything else. Please trust me on this. It may seem stupid and it does go against the recommended method used to capture images for a synth. If you use my method, maintain the overlap of photographs, and everything else will fall into place. I am going to send you a link to show you exactly what you need to accomplish the staircase synth. Give me a few minutes to find and upload the images.
jimcseke (Over 1 year ago)
Hey Jaleho, I am back with the link. Hopefully you will give my method a try. If you need more information, just ask. The total cost of materials is about $10.00
and you only need a bit of practice to feel comfortable with this method.
The type of camera set up I use is a bit more advanced than what I am showing you, but if you follow the simple directions, I am sure you will be pleased with the results. As you get more comfortable with the "trailer level" method, you might try using the "standard table level method" Both methods will increase the point cloud density and it's accuracy. Because of this method, I am able to edit my photograph to increase the point cloud density even more.
Chech out some of my synth. Most have before and after versions.
Maybe I can get at least one person to try this. If you try this and you like the results, drop me a link to see the finished version.
Oh you might need 2 sided adhesive tape. P.S. it works!
jimcseke (Over 1 year ago)
Some more advice here Jaleho, do a couple of small practice runs with maybe 100 or less photos and upload them. This will give you an sense of how you need to readjust your photographic habits. And as I mentioned, keep using the "trailer level" until you get used to it. And it does not take long to get used to this method. I would put the difficulty level in the same league as perhaps, learning how to use chopsticks for the first time. 
Cheers and have fun.
Jaleho (Over 1 year ago)
I notices that when I tried to take photos of a long stretch of land, by taking a shot, taking one step to the left/right, then taking another shot, it seemed that photosynth assumed I was instead, standing in place and spinning around, and tried to place the photos accordingly.

I've taken another thirty 360' shots of another position on the stairs where it looks like the altitude starts going crazy. I'll add those in tonight, and if that doesn't help, I may just have to pull out the tripod and start from the beginning, doing only 360 panoramas.

Still wish there was some way to "nudge" to program, to say "look, I know this photo is of this area and from about this angle... so just limit your search to this place and I'm sure you'll find a match."
jimcseke (Over 1 year ago)
I am not sure what you are trying to convey in your last comment.
I have to step out for a bit, so if you could explain in more detail what problems you are having, I know that I can help you out.
I will be back in about 2 hours.
Nathanael.Lawrence (Over 1 year ago)
Jaleho, I've seen the same sort of gradual warping that you describe when looking straight at something and walking parallel to it.

If you're going to start over, I would strongly encourage you to try something a little different and something straight out of the Photosynth team's own advice, even though I use it a little more heavily than they may have had in mind.

It is simply this: shoot an orbit of photos walking all the way around each step in the staircase. Keep the center of the step close to the center of your camera's lens (although this doesn't have to be perfect) and try to keep the tops and bases of the walls on both sides of the step in frame whenever possible. The nearest wall base will be obscured by the hillside when you are looking down and the other side of the wall when looking uphill, but don't worry too much about that.

I would be very surprised if this does not rule out the reconstruction errors that you have seen thus far.
Nathanael (Over 1 year ago)
I also should have said to try to keep both the front and back of the step in frame at all times. Again, as you circle around to look down at the current stair, the stair above it will be obscuring your view of the upper sliver of the stair that you are currently shooting. Don't worry about this either. The overlap of circling each stair will be more than enough overlap to get a satisfactory representation of the staircase in the pointcloud.

Once you have such a tight description of the staircase, other shots backing away from it for a wider view of the surrounds should link just fine as long as the size of any part of the staircase does not shrink to less than half the size that it was in the next closest shot of any part seen so far.
Nathanael (Over 1 year ago)
Taking plenty of shots while walking up and down the stairs as you did is not a bad idea at all (Jim actually did this a while back to great effect). The trick is to make sure that when you get to the top or bottom to take your time turning around to go the other way (I would simply treat the last step or the ground just beyond it as a tracking point and circle around it before looking back towards the rest of the staircase). 

In your case, since you aren't bound by railings or anything else that prevents you from backing away from each step a little you can actually easily build a far more robust reconstruction of each step and guarantee that the shot looking up and the shot looking down will bind to the surface of each stair seen in them.
jimcseke (Over 1 year ago)
Hey Nathanael,hey Jaleco. I am not 100% sure of what you are trying to accomplish, but I think the bottom line for you is to get a good photographic and point cloud representation of a central subject, which happens to be a set of stones steps. And of course with all the variables, such as topography, wrapping and all of the other aspects which could make or break a synth.
I am going to take a good look at the synth you are trying to accomplish.
I am sure that I could find a similar or even more complicate structure where I live.I will try to determine as close as I can what type of final view you are trying to create, and I will photograph a similar set of images.
The only difference is that I will be photographing the scene using my methods.
I will try to do it in one take and hopefully this will help you to decide how you will capture this scene. I actually try to find an area which is more complicated than the one you are attempting to synth.
jimcseke (Over 1 year ago)
So give me a day or so, as I do have a life outside of Photosynth (but just barely) and I will produce a synth similar or more complicated to perhaps give you a better idea on how to accomplish this scene. And I will include descriptions of how certain things work or don't work.
Nathanael has always been the "go to guy" on many topics of synthing. You can't go wrong with his advice.Hopefully between the 3 of us, we will create another synth addict.If you are new to this site, please don't give up. This technology is absolutely amazing, and the more you do the better you get...hopefully :) And your future synths, and other members synths will blow your mind.
I will drop a link to the complete synth here and perhaps on your most recent synth on your page.
Many synth problems are solveable. Or better yet Impossible is Nothing.
Chat with you later guys.
jimcseke (Over 1 year ago)
Here you are Jaleho. This typy of accuracy is only possible if you use the method I described. I could return to the same site tomorrow and continue synthing if I wanted to. And because all of the images are oriented in the same manner, any additional image would become part of the original synth. Maybe you get tired and want to continue the next day or for what ever reason.
I lowered the resolution of these images to 3 mega pixel. That is another advantage to photographing in this manner.There are so many matching references available due to the constant orientation of the camera, it is not required to upload any higher resolution. I like to upload images with at least 2 mega bytes of digital data. The synther is on a strict diet so I don't like to give her more than she absolutely needs. I also understand that there is less photographic noise in a lesser resolution. 
http://photosynth.net/d3d/photosynth.aspx?cid=794eef64-e777-4bf3-a814-3109311de55d
jimcseke (Over 1 year ago)
I took these photographs, and uploaded them without even looking at them.
100% synthy first time. And 100% synthy has a different meaning to me.
When I see 100% synthy, it is an indication that I will see something special.
And perhaps if some areas are weak, I am able to edit my photos in many different way.
So, what I am showing you is a way for you to get the best possible result using only on constant external reference. A trailer level. You will never be able to be confident of a synth outcome if you photograph the regular way.
If you need advice on how to get a good result using the other method, then I am sorry but I cannot help you with that.
I photographed some highlighted areas, just to show you how accurate this method can be. I noticed that you paid attention to a particular stone in the steps. I put my car keys on the steps to simulate that effect.
When I get a chance,I will add highlights in the edit mode.
jimcseke (Over 1 year ago)
If I remember correctly I highlighted a small ivy plant, a weed and some moss.
I also took an uphill side trail back to the top of the stairs.
One of the other cool features to this type of photography, is that sometimes unplanned for scene transitions occur. I haven't had the chance to view this synth or to give it the true test in a program like meshlab.
I can explain to you all the different ways to tie all of your images together, but for now, I think it would be cool if you went out and spent about $5.00 on a small trailer level and try a few practice runs for yourself.
Remember, these images were uploaded at 3 mega pixels. 
What is the resolution of your images, how large was the total upload and most importantly, how good was the result?
If you do not want try the trailer level I will not think any less of you.
But if you do try it, I think that you will be amazed at the results.
P.S. Be carefull near the edge of the cliff. It is a bit of a drop. :)
jimcseke (Over 1 year ago)
Please let me know what you think.
Nathanael (Over 1 year ago)
I've already talked to Jim about this, but for anyone following along it should be noted that regardless of what size your input photos are, today's synther only analyses small copies of each input photo (about 1.5 or 2 megapixels) to do the matching.

The full size images are uploaded for people to view, but the matching and positioning calculations are only ever done with the 1.5 megapixel copies.

Here are a few links where Photosynth team members have explained that.
http://getsatisfaction.com/livelabs/topics/what_image_quality_and_resolution_should_i_use#reply_579048
http://getsatisfaction.com/livelabs/topics/what_is_the_best_image_resolution_in_megapixels_to_use_while_cliking_pictures_for_a_photosynth#reply_582270
http://getsatisfaction.com/livelabs/topics/don_t_crop_images#reply_585680
http://getsatisfaction.com/livelabs/topics/whats_the_best_size_resolution_for_taking_pictures#reply_943216
Nathanael (Over 1 year ago)
Jaleho, I think that the closest scenario from the Photosynth Photography Guide that applies to your situation (in terms of not scrapping all you've shot so far and just adding a few corrective shots) is that of 2D synths where when you're looking straight at a straight wall, you do two different passes along it at two different distances.

I looked over your synth again and I believe that if you just do another pass looking straight at the wall that currently curves up into the air, but zoomed out more so that we see a little bit of the grass above the wall and some of the steps below the wall, that might make everything come out right. The grass isn't so important since it's been nearly six weeks since that first line looking at the wall was shot, but another pass looking the same direction where the height of the wall fills about half of the frame of your photos and most of the other half is filled with the steps just might do the trick.
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