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Author Topic: Some general questions about Photoscan  (Read 5538 times)

Sascha

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Some general questions about Photoscan
« on: April 27, 2016, 12:16:36 PM »
Hello,

i am using Photoscan Professional since about 18 months now, had about 20 projects and now some question came up.
If  you could help me on this, it would be very nice.

1. In the past we had some problem with the visualization of the 3D PDF.
On PCs with less RAM then 8GB the 3D PDF was displayed properly.
In the moment you move/turn it, the point cloud turns red.

I expect it to be a problem, when the PC does not have enough RAM.
Is there any value how much RAM is needed to display 3D PDF?

2. Point cloud accuracy

A week ago we had the question "which parts influence the accuracy of the point cloud".
Of course, the size of the pixels matter significantly.
Which other sources influence the overall accuracy, like overlap pf the pictures etc..?

3. Is it possible to view point coordinates in Photoscan?
Like picking a point and seeing the coordinate after implementing GCPs (overall error 5cm).

4. Last point in workflow menu is "create orthophoto".
The resolution of that picture is not as good as the resolution of the original pictures.
So if i want to perform measurements in that picture it is not very accurate.
An area which is 10 pixels in the original pictures is about 2-3 pixels in the ortho picture.


I am glad for any help you can give me.

Arie

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Re: Some general questions about Photoscan
« Reply #1 on: April 27, 2016, 01:34:05 PM »
Hi,
1. PDF files are not really optimized for displaying large amounts of points/polygons. Therefore a reduction usually is necessary. The red color is a indicator for a selection; so when your mesh/ points turn red it means you selected it.

2. The accuracy of the pointcloud is dependend on quite a few different factors. In lectures, I usually divide them into internal and external influences: Internal being everything involving the camera. To name a few, you have sensor noise (somewhat related to pixel pitch size), lens distortion, image sharpness (AA-filter, bayer pattern vs. monochrome, lens quality), depth-of-field vs. diffraction etc.
External factors would be things like image overlap, the type of object reflectance (diffus, specular, etc.), texture and structure of the surface, ground-sampling-distance etc.

3. Not quite sure what you mean with viewing point coordinates. AFAIK you can't pick a single point and view it's coordinate. You can do that with free software such as Cloudcompare.

4. Well, you can decide the geometric resolution of the orthoimage- so if you know a pixel in your original image has a GSD of 1cm, just set 1x1cm in the output tab.

Hope that helped-
Cheers.

JMR

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Re: Some general questions about Photoscan
« Reply #2 on: April 27, 2016, 01:50:54 PM »
I was answering at the same time as Sascha, so excuse if redundant.
1. Try using texture sizes that under  8192pix and number of triangles under 200.000
red model means it is selected, and not necessarily means a problem. zoom out and clic outside the model and it will turn normal again
2. Some Point cloud quality factors:
Texture quality. You would love textures that dont vary while point of view changes, randomly and evenly distributed all across the surface of interest.
Image artifacts. Avoid strong compression and over-processed images
Too much overlap (>85%) may make point cloud less accurate if parallel photos. This is not so true for convergent case.
poor overlap (<60%) may lead to clouds with more holes and less populated due to the increasing dissimilarity between images paired
best prime lenses give better clouds
good dinamic range and even lighting conditions are better than strong contrasts, shadows blacked out and clipped highligted areas
...
3 To view coordinates of a point requieres to use a marker and watch its estimated coordinates in the reference panel. A marker without given initial coordinates will act as a check point
4 Ortho resolution for scaled or referenced models is automaticaly recommended by Photoscan according to the optimal. It shouldent lower the resolution you have in source images unless your phtos are mixing very diferent resolutions. If you think you are loosing resolution you can increase the suggested value.

Best
GEOBIT

Sascha

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Re: Some general questions about Photoscan
« Reply #3 on: April 28, 2016, 03:12:17 PM »
Allright.

Thanks a lot to both of you.

Especially the part with the accuracy helped me a lot.

One thing remains unclear:

The check points

If i import GCP coordinates they are displayed in the reference menu.
If i now create a new point using "create marker" the point number is also displayed in the reference menu, but no coordinate is displayed.

Finding a way to do that in Agisoft directly would be nice, but the workaround using cloud compare is okay also, since i need cloud compare to create the E57 files. Picking points there and export the coordinates should be possible.

JMR

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Re: Some general questions about Photoscan
« Reply #4 on: April 28, 2016, 05:48:51 PM »
The markers estimated coordinates are only visible if you first click the button that shows estimated values in the reference panel, otherwise you will see empty coordinates.
You can export them as well is select estimated values in the export dialog
« Last Edit: April 28, 2016, 05:52:00 PM by JMR »

Sascha

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Re: Some general questions about Photoscan
« Reply #5 on: April 29, 2016, 02:13:21 PM »
Thanks a lot.

Found the button.

John_4dm

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Re: Some general questions about Photoscan
« Reply #6 on: May 03, 2016, 01:39:14 PM »
Hi Sascha,

Regarding your first question for visualizing 3D pdf and memory issue, instead of 3D pdf, you can use 3D data streaming functionality by uploading DEM, orthomosaic and pointclouds directly from Agisoft ( File->Upload DEM, Orthomosaic, pointcloud) to 4DMapper, then you can visualize, digitize, measure and share in full 3D with almost no high end computer or memory requirement. It streams the full resolution data to any browser which supports WebGL(most of the recent browsers support WebGL).

Btw, you can create a free account here to upload directly form photoscan: https://app.4dmapper.com/

John
« Last Edit: May 03, 2016, 02:18:14 PM by John_4dm »