Topics

1

General / Workflow with calibrated camera

« on: May 16, 2015, 05:26:41 AM »

Good day!
I`m mapping geological features called breccia pipes in Arizona along a huge gorge.
It`s gonna be a massive project (almost 1000 pictures from ground based camera stations)...

I`m using a Canon 500D plus a 35mm lens calibrated in Photomodeler using a grid of 9 sheets and coded target printed on them (calibration seems be pretty consistent according to the report).

For every camera position have been recorded coordinates on the ground using a DGPS in RTK mode (offset in altitude has been measured with a roll meter).
I drove on the other side of the Gorge to put several GCP, surveyed always with DGPS.

I  tried to process quickly just a few pictures to see which results could be achieved but I got a bit confused.
I noticed that reprojection error is surprisingly high...
I usually import my pictures, my calibration file (correctly converted using Agisoft Lens), tick fix calibration and run alignment step (in reference mode).
I would expect everything matching with topography known, but when I upload GCP coordinates, there`s a big offset sometimes...

So basically, what would be the correct procedure to be followed when I have all these data available?
I noticed that everything improves if I optimize camera parameters based on GCP coordinates...
Could be due to different conditions between calibration "environment" and field work?
(when I took pictures for calibration aim I was a couple of meters far from sheets, now I have to build a model of rockwalls far about 400/500 meters from camera stations...).

Should I let Photoscan calculate new parameters?

And if I didn`t have GCP on the other side, is there any way to model the gorge accurately and correctly just using the calibration file and coordinates of camera stations?

Thanks for any answers!
See ya

Davide

2

General / Lens Calibration in Photoscan processing

« on: January 24, 2014, 01:44:05 PM »

Hi everybody.
I wanted to know if anyone has developed a workflow in PhotoScan that includes the use of a calibrated camera for aerial purposes.

I generally follow workflow proposed by andyroo here http://www.agisoft.ru/forum/index.php?topic=1804.msg10373#msg10373.

I tried to calibrate the camera using Agisoft Lens but with poor results. I then re-calibrated camera with Photomodeler and then converted the file in Lens to use it in Photoscan.

My questions are:

• Can I import the calibration file obtained for starting to process the photos as usual and then use the GCP to improve the final quality of the elaborate?
• Have I to tick FIX voice in camera calibration window?
• What parameters should I optimize then using the GCP coordinates?

Thanks to all

3

General / Triangulation

« on: October 08, 2012, 06:39:22 PM »

Hi everybody,
I would know how Photoscan triangulate data...
In particular, when mesh is created, how it exports point cloud?
One point for each vertex?
One point for each triangle?
Is it place in the center?
Thanks

4

General / Photoscan vs Laserscanner

« on: October 01, 2012, 12:24:28 PM »

Good Morning.

Do I have some photos taken during a flight Lidar.
And there is also the point cloud Lidar and orthophotos.
I want to test the goodness of the point cloud extracted from the geometric model obtained from Photoscan with respect to Lidar point cloud.
I noticed that it gets a good planimetric accuracy but it's wrong a few meters in altitude.
I do not have the file available for calibration of the camera (Hasselblad CF-39).
The model has been georeferenced by taking the z-coordinate of the point cloud Lidar x and y coordinates from orthophotos.
I am looking for some advice to get better results.
I will add some screenshots to better understand the problem.
The purpose of this test is to be able to integrate in the future the point cloud we get through a terrestrial laser scanner with a cloud can be obtained through a photogrammetric analysis of pictures taken by UAV or aircraft.
Thank you very much.
David

P.S.: Is it always necessary to insert x, y, z coordinates of camera positions in pre-alignment stage?
        If I have only marker coordinates, are they usable for georeferencing model with more accuracy?