Sorry, I meant can you do a reconstruction on Preview - I would just be curious if there is much of a difference…
Hello Götz,
Quite revealing running Reconstruction in Preview, check out the spread of polys, quite heavy on the back cushion compared to teh seat cushion. Also, note the carved holes are largely filled in. Some aspects are quite acceptable, which tells me Preview could in fact be useful for very basic shapes.
gothic_preview_01.JPG
gothic_preview_02.JPG
Hey Benjamin,
thanks again!
Very interesting indeed.
I think that the polycount is quite close to your simplified examples.
It does however mean that there must be more differences between High, normal and preview than just the resolution.
And if you look closely, there are unintentional spikes on flat surfaces, which influences the appearance quite a bit.
In the end it is a matter of scale - do you want a closeup model with all intricate details or is it a prop in a larger setting.
And if you squeeze that last one into 50.000 and compare it to another 50.000 based on a high detail reconstruction, I bet you have to use software to visualize the small differences…
Ok, people.
Lets imagine 3 different dataset. 1st from Nikon D810, 2nd from Canon PowerShot G7 X and 3rd from Samsung Galaxy S7.
All have datasets have camera in same positions. And the same image resolution, lets say 12Mpx.
How work modes in RC:
Draft - 3~4x times downscale images, minimal mesh optimization.
Normal - 1~2x times downscale images, mesh optimization and refinement.
High - No image downscale, maximum mesh optimization and refinement.
So on default settings, there is no question about Draft/Normal/High, Draft use 3-4 times smaller images for Depth maps, Normal - 2x smaller, High - Full resolution.
All datasets except Samsung one will have more details and as result bigger mesh count in High comparing to Normal. Samsung probably near the same 
If you change default settings to Normal and disable downscale. There will be a different result.
Probably only Nikon D810 dataset will have much more details in High due to sharp images and no AA filter. And more mesh calculation steps comparing to Normal mode.
G7 X Probably will have the same amount of details and probably a bit bigger pol size. Actual details will lost due to lower amount of details (AA filter, ISO noise, etc, chipper camera).
Samsung dataset in High mode just will have increased number of poly without any real details.
So if you have sharp, clean dataset with good overlap, good textures, low reprojection error after triangulation etc. And if you need maximum possible details, you can use High.
If you use middle class camera, often making errors in overlap, dof, etc. Normal with disabled downscale is enough.
If you use smartphone camera, than you should not use High because it not give you more details.
Thanks, Vladlen, that all makes perfect sense. I’ll start paying attention to the reprojection error after triangulation to compare against various shooting conditions in better training my eye how best to shoot.
Götz, I’ve only run the chair in High and Preview, might be interesting to now see what difference there is in Normal. The issue with holes in the wood carvings should present a difference, given my 52 MP Sony A7rii shot the chair from 1.5 m will plenty of light to sustain high dof.
Make real hay in the meanwhile, I’ll follow up.
Many thanks, both of you.
Benjy
Hi Benjamin.
If you can show camera placement for this chair scan and some images (crops with only chair is enough), i probably can tell you the reason of this problems.
As i can see your raw mesh, for this moment probably 2-3 reasons:
Wrong acquiring (some surfaces have angle 45degree and more on images) or not have good coverage and overlaps.
Reflections or light spots on reflective surfaces.
Or surfaces with weak textures shot too far from them.
All this can be a reason that some areas on mesh have huge size polygons or holes.
Hello Vladlen,
On the road the last couple days. The attached snip shows the convergence angle between cameras isn’t near 45 degrees relative to the chair, which in most of the wide shots upper three rows fills the frame. The two lower rows I move closer and shoot landscape mode, the whole lower part shows in each frame, cropping the top. Then you see the much closer stills from the front and the back to capture all the detail of the carved wood left and right of the back panel. I checked critical focus throughout. No shiny spots, light is cross-polarized for pure diffuse.
Gothic_Cams.JPG
As for what geometry RC is able to glean from the photography, I was kind of shocked to see an extremely subtle difference in how the threads of a given color in the woven design sit lower than neighboring colored threads or thread types:
Gothic_weave.JPG
One mistake, I should have moved in to the close ups more gradually and/or worked the close ups around from the front to the back and back to the front, the model suffers from one real flaw - the lathed finials upper left and right have the front half slightly offset from the rear half. The wood contains plenty of grain in the texture for the engine to grab onto, but there’s nothing relating this detail around this symmetric shape around from front to back on both sides to model it properly.
Best,
Benjy
Hello Benjamin.
I did not see any camera from top. Them just not seen on screen, or you don’t have them?
Anyway, i’ll show some schematic images how camera should be.
First of all, we must remember, that photogrammetry required not silhouette of object but surfaces and details (textures).
Now lets imagine simple chair:
It have surfaces that points top, sides and bottom.
Capture1.JPG
Capture2.JPG
Capture3.JPG
So we Must Have at least 1 image directed toward to the surface.
Capture4.JPG
And not less than 2 images in 10-15 degree to first camera.
Capture6.JPG
Central camera will give you perfect texture, other two with will give clean Depth maps (and later clean Dense Clound) for this Central camera required for calculation 3D topology.
And this must be for Every surface you want catch! Every surface in ideal condition must have 3 shots.
But if we have surfaces that attached in high degree (90 degree like in example) we need additional images shot for “stitching” Dense Clounds in angles between main camera triplets.
Like this.
Capture5.JPG
So “final” scheme will looks like this:
Capture7.JPG
So we already have 15 camera only for 3 surfaces!
Ok, in real world with good camera like Nikon D810 and good lens we can “cheat” and use only 5 camera.
But for this example with 3 surfaces at 90 degree all, even from D810 result will be not perfect.
So i can’t recommend shoot less than 11 images
Capture8.JPG
or this will be not enough data for clean depth maps->dense clouds-> mesh, textures, and as result final topology will have less details or will have problem in topology (especially if object have weak surfaces).
And now if we see any nice object that we want to scan, we can plan where and how many images we should have for clean topology and textures.
Also we should remember about real camera and lens. Them can have DOF, aberrations, non linear distortions (last two problems common for area near corners and edges of photo). So real, good data from image is about 75-80% (sometime less) in center of image. And all this can required additional images for good 3D reconstruction.
Thank you Vladlen,
Nice job breaking that down to ideals and illuminating the issues with lenses. I need to modify my thinking when considering how I break an object down from the macro structure to the micro scale of finer details, do a better job providing transitional shots to move from one to the other. When working on a piece of furniture like this, even a slightly converged view of the seat provides plenty of texture data, no need to shoot directly from top, especially given my imagery is 52 MP. A chair is one thing, but I try to maintain a 2 meter distance to the macro structure of cave walls when capturing environments. So much is going on in a crazy environment, model coming along nicely, but definitely need to take more photos, spending more time than should be necessary setting tie-ins.
Big thanks for your guidance!