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Messages - Kiesel

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271
General / Re: Dual cameras for better results in Photoscan
« on: December 16, 2014, 09:29:57 AM »
Quote
Now if you have two cameras positioned in an ideal angle, the success rate for these image pairs will always be 100%, though between n image pairs there might still be variance in terms of the number of successful points. I'll hypothesize that on average you'll get more points generated with a dual camera rig than a single camera with equal numbers of pictures in the data set. And I'll hypothesize that this will be true no matter if the subject is static or moving slightly.
That was meant with the advantage of "allways working stereo pairs".
Quote
Do anyone know the ideal angle between two cameras BTW?
It is a compromise of ideal intersection angle (a little bit more than 90 degrees) and better feature matching with closer angles. But generally the ratio between stereo base and distance should be in the rang of 1/5 to 1/10.

Karsten

272
General / Re: Before I begin digging in...
« on: December 15, 2014, 07:12:55 PM »
Hi Scanning_newb,

when I saw your object I thought that it is probably easier to go to a local foundry for casting directly and make a casting mould from it.

Nevertheless you want to know how you can do it with PhotoScan. At first I should mention that I have never reverse engineered something by myself so just an idea how to do it after PhotoScanning.
Generally I would choose a turntable solution or something similar. To scan the outside should be no problem, I think two rounds of 24 photos (one photo every 15 ° one round horizontal and one from a little bit above) should do it. The 1/2" NPT thread isn't completly scanable only a little bit of it and where it is. But before scanning remove the three little screws. and put a ruler next to your object or measure something for example the diameter for later scaling.
For the inner part I would turn the object so that it stands on the hexagon head and take one or two other rounds ideally in such a way that there is also something from the outside in your photos. Because it is otherwise tricky to combine inside and outside. Additionally you could lay your object on the side, like in your second photo, and take another round. For both use a high aparture like F22 because of DOF issues.
Then aligning, editing the sparse point cloud, optimise, scaling (if you have the Pro version) and dense point cloud generation, I won't do meshing as it is difficult to use the triangulated mesh in CAD but for later measuring it could be useful.  After that you can export your point cloud and scale it if you have only the standard edition (you can do it in a 3rd party program package like Meshlab, ...).
Because your object consists of a body of rotation - the bell - and a hexagon head, I would additionally cut the point cloud in a thin slice along the rotation axis. This point cloud slice I would use in a CAD envirement to draw a curve over it and then rotate it around the rotation axis. The hexagon head could be easily measured with a vernier caliper.

To elaborate? Go to a local foundry for casting directly  ;)

Karsten


273
General / Re: Dual cameras for better results in Photoscan
« on: December 15, 2014, 05:18:27 PM »
Of course the better scan quality came in this case from no movement between shots. The use of the known distance between cameras inside PhotoScan was an old feature request and seams now been implemented, thank you to Agisoft team. Another advantage is besides faster shooting that you have allways working stereo or triple pairs.

Karsten

274
General / Re: Dual cameras for better results in Photoscan
« on: December 15, 2014, 12:58:09 AM »
Yes, Mark Florquin with three cameras see:http://www.agisoft.com/forum/index.php?topic=970.msg4733#msg4733

Karsten

275
General / Re: Before I begin digging in...
« on: December 15, 2014, 12:48:38 AM »
Hello Scanning_newb,

please describe your problem as precise as possible, do you have some photos of your object to share?

The outside of an object is normally no problem as long as it have enough structure/texture, isn't shiny and has no extreme structure with hidden parts.
The inside could be difficult if there is not enough space to get your camera in, there is to less distance between camera and surface so the camera can't focus or you have difficulties with to less DOF. Then smaller cameras with good makro modus can help. When even this failed you can use a mirror. But with mirrors you can get difficulties with the texture, because you get virtual camera stations (without mirror) from which the photos are projected sometimes through your object.

But all that you can try with the demo version of PhotoScan and don't need a full version for that or you order an evaluation code.

Karsten

276
Hello Mark,

fascinating project, well done!

I think the biggest problem is to concentrate yourselve for every photograph taken and allways have enough overlap. Do you have to reshoot some segments because of lost alignement, gapes?
What do you think of the new fisheye support of PhotoScan would you use it for such a project?

What have you done with the texture, because I think even a 16k texture is not enough for such a large project?


Karsten





277
TheBlueBear

The example of face scanning was only used because you used it at reference for scanning quality.

Quote
You mentioned 6 cameras on a face being related to a GSD of 0.1 mm.

No, it is the photographed (scanned) area. For example a Canon EOS 1200D/REBEL T5 has a sensor resolution of 5184x3456 Pixel, so if you photograph an area of 500 x 340 mm, a little bit more than a human face, you get a GSD of around 0,1mm, 10 pixel on the sensor for every mm in object size. So you can choose the GSD by focal length (wide angle, normal, tele, makro lens) and distance from camera to subject/object.

The use of 6 or more cameras has nothing to do with the resolution you will get. But the more cameras are used to scan the same area the better is the modeling, because you have more ray intersections from the six cameras than from only two and PhotoScan can build a better mathematical model of the scene. A good photo shooting technique, shooting more than one row, one from below, one from normal position and one from above, good overlap, good intersection and adding some left and/or right rolled photos can help PhotoScan a lot. See also the manual of Agisoft Lens for that.


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Frankly, I don't really understand how Agisoft selects which image (or pixel) to use when the same area is covered by multiple photographs.

For this Photoscan use something like SIFT (see http://de.wikipedia.org/wiki/Scale-invariant_feature_transform). At first it generates keypoints for every image and then compare these points from image to image. From the common points it can calculate the camera calibration, the positions of the cameras and the sparse point cloud. All this is done in the Align step. But this is nothing you have to think about just let PhotoScan do the math  ;). But you can help PhotoScan a lot with the photos you shot see above.

Karsten


278
TheBluebear

To your question:
Quote
It is much better but still a world away from some models that I have seen of faces.
Do you have any sense of why I am not getting their impressive results?

At first it is a question of resolution of the used photos and with resolution I don't mean the Megapixel of your camera but the GSD (ground sample distance see http://en.wikipedia.org/wiki/Ground_sample_distance) you get on your object/subject. In body scanning there are aiming 6 or more cameras to the little area of a human face so they get a GSD of 0.1 mm or better for each pixel. And even then the results are not so impressive as what you have seen. Search for results of raw scans as they came out from PhotoScan to see the quality you can get with it. And second the results you have in mind are a product of a special workflow in third party programm packages like Zbrush to improve the results from PhotoScan.

But you don't need the same resolution for the scanning of facades, one to five millimeters GSD are enough if you want to see details of 2 mm to 1 cm (you need (a little less than) two pixels to see a difference in contrast, like an edge, in your image).
On the other hand facades are very different, PhotoScan "likes" texture rich old fashioned stone facades but "dislike" texture less, even or shiny modern steel-glass facades (even laserscanners have difficulties which such facades) at all. For the modern facades you can go for example with rectified images, classical photogrammetry packages where you have to pick every point of interest in every image or/and a total station.

Karsten

279
General / Re: Generate allready scale model
« on: November 25, 2014, 05:51:59 PM »
This has nothing to do with camera calibration at all! You can fill your photograph with a coin or with the moon ;), it has only to do with image scale.
So you need something of a known length in some of your photographs and then you can use it to scale your model (scale bar function in PhotoScan Pro or with a 3rd party software like the free Meshlab or CloudCompare for PhotoScan Standard).

Karsten

280
General / Re: Aerial Photogrammetry Phantom 2
« on: November 18, 2014, 06:07:23 PM »

281
General / Re: Aerial Photogrammetry Phantom 2
« on: November 11, 2014, 05:51:24 PM »
Hello Mortarart,

for me your link to your camera mounts is unfortunately not working.

Karsten

282
Feature Requests / Re: Photoscan Professional "Artist" Edition
« on: November 11, 2014, 05:46:19 PM »
Thank you again Alexey, I was indeed looking for an "Optimize Button" before I found it in the "Tools Menu".
Tiny suggestion:  Could there please a little warning if a point cloud or/and mesh exists that the optimizing will erase both?

Karsten

283
Feature Requests / Re: Photoscan Professional "Artist" Edition
« on: November 07, 2014, 08:55:24 PM »
After a little searching I have found it now under "tools".
Great! Thank you Dmitiri (the main man in the background), Alexey and all others from Agisoft team! :D

284
General / Re: Masking and its effects for point cloud and mesh generation
« on: October 29, 2014, 06:36:04 PM »
Masking is a must when the relation between subject/object and background isn't stable. Moving subjects/objects before background - for example in a turntable solution- or moving background - clouds, people, cars, leaves, ...!
When your subject/object has enough textures and is large enough to fill your photo you can mask out all parts you don't want and need. Often this improves the quality of aligning and mesh quality, otherwise if you have long small or thin items it could reduces it,  so it's depending on your subject/object.

Karsten

285
General / Re: Textures from point cloud
« on: October 29, 2014, 06:11:13 PM »
Hi bmc130,

as Mark said, should be possible in Meshlab from PLY:
Go to FILTERS / SAMPLING / VERTEX ATTRIBUTE TRANSFER

Have a look at http://www.cse.iitd.ac.in/~mcs112609/Meshlab%20Tutorial.pdf Page 43.

Karsten

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