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Author Topic: Photography Tip!  (Read 8314 times)

zhr69

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Photography Tip!
« on: March 28, 2015, 02:47:21 PM »
Hi Everyone,

I want to model a cup using Photoscan. What is the best camera positions while taking photos? My camera positions is shown in attached picture. My problem is with edges.

What is your ideas?

Alexey Pasumansky

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Re: Photography Tip!
« Reply #1 on: March 31, 2015, 06:05:03 PM »
Hello zhr69,

I think that the problems are caused by the lack of texture inside the cup, so the dense cloud is noisy inside and close to the edges, and so is the mesh model.

I think that the reconstruction of the inner part would be better, if the cup is covered with coffee grouts, for example, from inside :)
Best regards,
Alexey Pasumansky,
Agisoft LLC

zhr69

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Re: Photography Tip!
« Reply #2 on: April 03, 2015, 10:36:26 AM »
Thanks Alexey for your helpful guide.

I did it and my model seems so better. I have attached my new model too. For now I have two problems:

1-  Texture model: To achieve clean texture I get two series of photos of my model and generate two distinct model. Covered model is good (as you can see in attached photos) but uncovered one is so bad. how can I use texture of uncovered model for it? What is the best alignment method?

2- Size of photos: My camera has 21MP resolution. But when I take photos with this size the result is not good. I have to take photos in 2MP resolution to achieve better results. Do you know what is it because? My settings is default Photoscan values.

So thanks in advance.

zhr69

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Re: Photography Tip!
« Reply #3 on: April 07, 2015, 09:24:22 AM »
I need your help. Could you please guide me more?  :'(

Marcel

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Re: Photography Tip!
« Reply #4 on: April 07, 2015, 10:15:56 AM »
If you need to downscale your photos t get good results, it generally means your photos are not sharp.

Could you show a few source photos at full resolution? It's hard to give advice without seeing exactly what you do.

zhr69

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Re: Photography Tip!
« Reply #5 on: April 07, 2015, 11:56:57 AM »
Thanks for your reply  :)

I've attached cropped images due to attachment restrictions. I'll be glad to see your comments.
My big problem is texturing. I want to align clean model with covered model and use clean photos for texturing. How can I do it by using Photoscan?

Marcel

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Re: Photography Tip!
« Reply #6 on: April 07, 2015, 02:30:32 PM »
I'm not sure if that is possible without a multi camera rig.  With a multi camera rig you could Align and build the Dense Cloud with photos of your object in 'covered' state, and then build the texture in 'clean' state. (the photos are in the exact same position). If you are using handheld photos or a turntable then it will be very hard.

Pixel UAV

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Re: Photography Tip!
« Reply #7 on: April 09, 2015, 08:01:19 AM »
i may be able to help with the camera resolution and the quality of the model
It is all about the size of the pixel on the cup, known as Ground Sampling Distance,GSD, by aerial photographers. 
Since you have a high resolution camera and are taking your photos from a very close range, im guessing no more than 30cm away, the size of the pixel in real life is going to be very very small, under 0.1mm i would guess.  When photoscan makes the dense point cloud the quality you choose dictates the density of the point cloud based on how many pixels will be used.
Ultra High:Every pixel
High:Every 2nd pixel
Medium: Every 4th pixel
low:Every 8th pixel
Lowest: Every 16 pixel
i.e. If my ground sampling distance was 1mm and i choose medium quality, then the dense could would use every 4th pixel in a photo to produce its dense cloud.  therefore i would have a point every 4mm
the lower quality images would produce a better result because the GSD is lower so smooths the models out. if the GSD is to high then you end up with a lot of "noise" in your models as there is always a certain amount of error in every point, which becomes very apparent when you have a lot of points very close together.

My suggestion to you is to decide on how far apart you want the points on your cup model, then adjust your photo resolution to be 4x better than what you want.  This will give you room to play when you produce your dense point cloud.  There are GSD calculators our there.
 I hope this makes sense and note that massive resolution cameras are not the be all and end all of photogrametry.

zhr69

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Re: Photography Tip!
« Reply #8 on: April 12, 2015, 05:05:11 PM »
Thank you all for your replies. I understand the relationship between images resolution and the quality of the model.
But I'm still confuse about texturing. I have two series of photos (Covered and not covered) which pick them using turntable solution. How can I texture my covered model using clean photos? Any help would be appreciated.

igor73

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Re: Photography Tip!
« Reply #9 on: April 12, 2015, 09:44:45 PM »
Someone suggested above that you need a fixed multi camera rig to do that easily.  That way you are sure the object and the cameras  is in the exact same position when you project the images.  As you don´t have that it will be more difficult.  You do have some options though but they are more advanced.  I have not tried his but you could duplicate the chunk with the non covered cup and then import the covered cup mesh in to that chunk.  The Cup will probably be the wrong scale and position.  You then have to manually scale and move it until it matchs the original cup position of the un covered cup.  Not sure if this can be done in standard version but i think it can be done in the pro version.  You then build thexture and select keep UV. 

Other options are manually texturing the cup in a 3D modeling program using your images of the un covered cup as reference.  If you have some skill you can get an accurate result.  I would use Zbrush´s spotlight for this.  It must be a very unique cup for it to be worth it though  :)

I guess yoo are only using the cup as a practise object right? 

zhr69

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Re: Photography Tip!
« Reply #10 on: April 14, 2015, 05:36:44 PM »
Hello igor73,

Thanks for your reply. Yes, I am currently using the cup as the model. It is complex model due to shiny and texture-less properties.

I have not multiple cameras. I have one camera with a turntable.
About your first solution, I can't align correctly two models using manually scaling and moving.
About Zbrush´s spotlight, I will try it and let you know the results.

Any other solutions would be appreciated.

James

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Re: Photography Tip!
« Reply #11 on: April 14, 2015, 06:39:12 PM »
1. Place 'clean' cup on a textured surface, such as carpet/newspaper/wood etc. Ideally glue/nail/screw/velcro it down!
2. Take your photos of the clean cup, and also photos of the textured surface without the mug visible, with lots of overlap between.
3. Cover the cup with paint/coffee/powder etc whatever you need to reconstruct a good model, but do not move the cup.
4. Take a load more photos similar to step 2 above
5. Add each set of photos to its own chunk, and align them individualy.
6. Try aligning the chunks together using point based method.
7. If it fails alignment because the mug looks too dissimilar between chunks then mask the mug out before aligning chunks.
8. If it still fails, then duplicate both chunks and from the duplicate chunks delete all photos with the mug visible (this is why you take photos of the surface alone in steps 2 and 4.
9. Align these two small chunks together using point based method. It should work because it is only a few photos of a textured surface which should look identical in the 2 chunks. Then merge the chunks.
10. Now align the merged chunk from step 9 with the 2 original chunks from step 5 and align using camera based alignment.

Some combination of those steps is bound to work, and should all be possible in standard version of photoscan. The challenges are to:

a) find a nice textured surface - newspaper or wood would be ideal really
b) cover the mug in something without moving it on the textured surface
« Last Edit: April 14, 2015, 06:42:01 PM by James »

igor73

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Re: Photography Tip!
« Reply #12 on: April 16, 2015, 01:33:39 PM »
Great advice james,  like the idea of using the textured surface the object stands on for aligning. 

zhr69

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Re: Photography Tip!
« Reply #13 on: April 17, 2015, 06:46:36 PM »
Hello James,

Thanks for your solution. It was great and should work. I have problem with covering the model without moving it. I got the photos of clean cup and it moved a little when I had covered it. It is so hard work because I can't glue my object on the surface.

Anyway I like your solution.  :)

Is any other person who has different experience?
« Last Edit: April 17, 2015, 10:48:54 PM by zhr69 »