Topics

1

General / camera accuracy meaning

« on: January 31, 2017, 06:54:19 PM »

Hello everybody.
I still don't have clear the meaning of camera accuracy into the reference panel. Does it refer to the accuracy of the GPS data of the images? If so, 10m would need that each camera position can have a max error of 10 meters. Is this a total XYZ error? Should I encrease it according to the precision of the GPS device? how does this affect the alignment of the images? If I set a wrong parameter could the alignment be unsuccessful?
Thanks.

2

General / disappeared camera position with GPS data

« on: January 31, 2017, 06:42:16 PM »

Hello everybody,
I'm working on a large dataset (10000 photos). Each photo has coordinates (WGS84 ellipsoidic) in the EXIF data. After I made masks, now I can't see their position into the scene anymore.
I've tried with...clear in the reference panel, switch to local coordinate(m), reset transform, change reference system, import a txt file with camera GPS data. However I can't see them into the scene as when I add them in a new chunk. I would need to display them in photoscan before running the alignment. How can I fix the problem?
Thanks in advance 

3

General / Select points by shapes (polygons)?

« on: August 09, 2016, 01:58:02 PM »

Hello everybody,
I'm working on aerial imagery and I need to remove some features (barracks and vehicles) from the pointcloud in order to create a cleand pointcloud and a DTM.
Identifying such features on photos or orthomosaic is easier. On photos I might use masks and select points by masks, however it's hard to recall what you have masked or not. It's far easier on orthophotomosaic to create polygon shapes around objects, export them, and import them again onto the pointcloud as shapes.
How can I select points by these shapes automatically?
Thanks.   

4

General / Keypoints-Tie points, calibration parameters and optimize..tests and doubts

« on: July 25, 2016, 03:59:39 PM »

Hello everybody,
I know that some posts have already been written on such issues but I've still some doubts.
I'm currently working on an aerial photogrammetry project and I've tried some tests.

1st test, Camera calibration parameters.
The camera (ILCE-7 35mm fixed lens) has been calibrated into Agisoft Lens. I've performed the alignment of a subset of photos 3 times: precalibrated with "fix calibration" on, precalibrated with "fix calibration" off, auto.
After the alignment (high accuracy, generic preselection) with the last two modes photoscan gives me into the "Adjust tab" new intrinsic parameters which are pretty different from the Pre-calibrated ones. As said in other discussions on the foum, due to the different environment conditions and difference of focus settings between the calibration process with Agisoft Lens and the shooting phase we can get different values. Moreover looking at the three chunks "show info", the first mode gives higher RMS and Max reprojection errors while the second and the third mode give very similar errors.   
There's a difference between the 2nd and the 3rd mode, the latter doesn't calculate any k3 and k4 parameter.
So the adjusted parameters are more reliable and that we need pre-calibrated parameters only to make photoscan consider the k3 and k4 parameters, can you confirm that?
Since the k3 and k4 parameters are not 0, must they be set on "fixed" into the next optimize process?

2nd test. Alignment KeyPoints and Tie Points number.
I've lunched for the same images subset 4 different alignments varying the number of Key Pt and Tie Pt: 40k-4k, 40k-0, 80k-0, 120k-0.
The number of tie points I got is between 120k of the 1st chunk to over 2 milions of the last chunk. I can notice by the Show_info that the more the KeyPt-TiePt number the lower the Reproj Error. The difference is not very high (0.9 in the 1st, 0.7 in the 3rd and 4th) but I've noticed that using the gradual selection and putting the limit of 10-15% of TiePt that can be deleted, I can reach the 0.5px of RMS Reproj error in the 2nd and 3rd chunk.
It might imply that using a higher Key Points number and 0 Tie points give you the chance to delete a lower percentage of points and to reach a lower reprojection error by the gradual selection and optimizing. What do you think?
Using the gradual selection Image Count bar I would like to remove all the Tie pts which are only in 2 images since I think they are responsible of much of the noise. In all the chunks I would remove almost 50% of all points which is maybe a too much high percentage but into the 4th chunk (120k-0) I would still keep over 1 million of points that is far higher than the total number of pts I have in the 1st and 2nd alignment. Can I remove so many points after setting a higher number of Key Pts and Tie Pts in the previous alignment process?

If I'm going to perform an optimize based on GCP what's the need of the gradual selection optimize....I mean does the GCP optimize delete the previous gradual selection optimize or Photoscan gives them some type of weights?

Regarding the "update tool" after placing the GCPs, what kind of transformation (affine,conform...) can be performed?

Thank you all.