Best practices for tank scanning

[tarkhil]

Screenshots or it didn't happen 

Repeating: https://drive.google.com/folderview?id=0B2oEX4lg2uEtWFM5eGlsZEs2OE0&usp=sharing

all images avaliable, as well as projects.

[tarkhil]

I had a quick play with some of the images. In general I'd say that the camera angle tends to jump around a bit, and in some cases there aren't really enough images to provide adequate information of the detail of the tank that you focused on.  I'd suggest trying to be more methodical in your approach to taking the images. Whilst it's not entirely necessary, it helps when you're starting out to have each image overlap part of the previous image. Focus on getting an overall set of images for the tank and then move in on specific details and you should find it easier to get a good result.

You see, there was one thing more important to me than making good shots: not to fall off tank or pedestal. Quality of resulting 3D model would be too low in that case.

And I'll print markers on soft magnets, it must be great for tank shooting.

[MartinBim]

you need just a lot!!! more fotos

[tarkhil]

First of all, I need more RAM (yes, I do have it now).

[tarkhil]

I've suddenly run into strange alignment problems.

I've limited model to front details of tank, since I have only 16 Gb of RAM and cannot install more in my present notebook.

https://drive.google.com/folderview?id=0B2oEX4lg2uEtdWw5dVdodnBKMjA&usp=sharing

project t34front

Some photos - MANY photos - are not getting aligned.

What can I do to fix the problem? More photos? From which points? Maybe some hint to PhotoScan, to help it place photos in correct places?

[Marcel]

I've suddenly run into strange alignment problems.

I've limited model to front details of tank, since I have only 16 Gb of RAM and cannot install more in my present notebook.

https://drive.google.com/folderview?id=0B2oEX4lg2uEtdWw5dVdodnBKMjA&usp=sharing

project t34front

Some photos - MANY photos - are not getting aligned.

What can I do to fix the problem? More photos? From which points? Maybe some hint to PhotoScan, to help it place photos in correct places?

Not more photos, better quality photos. If you photos are sharp, then Photoscan will have no trouble aligning them.

This is how your photos look at 400% magnification (click on thumbnail):



There is a lot of noise in the photos (in the dark areas especially), to get less noise you need to shoot at ISO100 instead of ISO400. (and like I said: you need a tripod and remote shutter release cable for that).

There is also a lot of JPEG compression on your photos:



See all the blocky stuff? Photoscan has real trouble recognizing any features because of the compression.  Try re-saving your JPEGs at 100% quality.

For a quick fix you can also try to Align at "Low" quality. This will downscale the images to 25% of their original size, which has the side effect of making the images much sharper. Sometimes this helps.



Edit: The other shots you did (when there was full sun) are much better quality:



Nice and sharp, and no JPEG compression. If all your photos would be as sharp as this, there would be no problem with the alignment. These photos do have other issues however: the specular shine on the object varies with the camera position, and this is not ideal. Photogrammetry isn't easy 

I'n not sure if mixing photos with such different lighting conditions will work, probably not.

[Marcel]

Note that the markers are interesting, but really not needed to get a correct alignment. There is plenty of small details on the tank for Photoscan to use. Unless you use them for scale reference ofcourse.

[tarkhil]

Will saving as tiff help? I've tried to save with 100 quality jpeg and do not see much difference. Maybe I'm doing something wrong in Lightroom/Photoshop?

[Marcel]

Or maybe Google Drive compresses the JPEGs I am downloading, that could also be?

Tiff would indeed be lossless, but the filesize is much bigger so projects can take up a lot of diskspace.

[tarkhil]

I don't think google does something transparent with my files. I'll try to redevelop all files manualy

[tarkhil]

Looks like I've managed it!

https://drive.google.com/folderview?id=0B2oEX4lg2uEtTHJnZW5LUHVKRjg&usp=sharing

My notebook can process only a little model in finite time, but quality seems to be passable.

Maybe someone can make some suggestions on improving quality?

[Marcel]

Good stuff!

I see you managed to get a tripod, that makes a lot of difference.

There are still some blurred images, for example DSC_6154.JPG. Are you using a remote release cable? Because when you push the shutter button on the camera using your finger, it's very easy to move the camera too much. Even the shutter action can move the shot, so for absolute perfect results you can use Mirror Up (if your camera supports it).

I would go through all your images and remove blurred ones (like DSC_6154.JPG). This will improve the quality of your scan. Don't forget to use Optimize Cameras after you have removed those photos from your chunk, or redo the complete alignment.  Images that are very slightly blurred like DSC_6172.JPG can cause noise in your surface. You have more than enough shots, so do a very strict selection and remove anything that is not completely sharp.

Layout wise: having your camera in the same spot and shooting 'panorama style' is less useful than giving each photo a different position. You could lower your ISO to ISO100 to get a tiny bit less noise.

[tarkhil]

Minimum ISO is 200 on Nikon D300s; I have "low -0.5" and "low -1", but they does not seem any useful.

I've tried to make shots from three different heights and shift about 1 meter side on each set. I do understand about different position for each shot, but I cannot get closer to tank due to the fence.

Right now, passable quality of mesh has been achieved. I have now (a) find more, much more hardware for dast processing and (b) find a tool/develop a procedure to make good model from mesh.

And I do need a crane for shooting top. But it's not a matter for this forum.

Thank you and wish me good luck and purchasing of a PhotoScan soon

[igor73]

Instead of a crane you could use a drone.  As for software to make your mesh game ready i would suggest Zbrush and maybe Topogun for re topology if you need to go very low poly.   Xnormal for normal maps if you want best possible quality. 

[Marcel]

I've attached a schematic drawing that shows what I mean about positions. Photoscan can get more information from a photo when the camera position is different (instead of only the angle being different). It is fine to rotate the camera and take two shots when the subject doesn't fit. But I don't think it helps taking 5 shots that have a lot of overlap.

ISO Low -1 might still be useful. What it does is expose the photo 1 stop brighter, but it scales back the values so it does not look brighter. The overexposed photo has less noise in the dark areas, but the highlights might suffer.   It depends on your subject if ISO Low is useful. If your subject includes a lit of white highlights (like the snow in your tank images), then ISO200 is probably better.

I played around with your project, the point cloud actually has slightly less noise when you process it at Medium instead of High, and you do not loose much detail (and as a bonus the processing is much faster).