How To Add A Camera In Sfm

Qimera

How-to Qimera - Construction from Motility (SfM)

Structure from Movement (SfM)

This how-to briefly explains how Qimera's Structure from Motion (SfM) Bathymetry tool works.

The Construction from Motion (SfM) can be used to correct for refraction errors in submerged data acquired from airborne photogrammetry.

Because of the big density difference between air and water, calorie-free reflected off submerged objects and observed from the air volition be significantly refracted. From an airborne camera's perspective the submerged objects volition appear shoaler than they are in reality.

While the refraction correction is dependent on the angle of incidence with the water, with photogrammetry the exact angle of incidence of any given point is unknown because it is the combination of multiple camera positions.

There are ii methods available to estimate a correction:

1. The Dietrich Method - tries to find all the photographic camera positions or images that may have contributed to a point and averages the correction.
2. The Small Angle Method - does not remove all refraction errors, but removes a large mistake which is easy to model and correct for even with an unknown incidence angle.

The Small Angle Method only requires the Water Height & Refractive Index. It tin be used if you do not have access to the original projection with information on camera parameters and position/orientation.

Structure from Move (SfM) Bathymetry Dialog

Structure from Motion (SfM) Dialog

How to Outset

• Make a selection of Sonar Files → Tools → Utilities → SfM Correction...

SfM Correction from Tools Menu

License

To run the Structure from Motion tool, Qimera requires a valid and activated SfM Bathymetry Add-on to the license.

License Managing director - SfM Bathymetry Improver

What information technology Does

The Construction from Movement (SfM) tin exist used to correct for refraction errors in submerged data acquired from airborne photogrammetry, commonly referred to every bit "Structure from Move", or SfM.

This tin exist applied to Processed Betoken Files.

This should non be used in conjunction with the Z-Shift Data filter (encounter Manage Filter Profiles), every bit it volition remove whatsoever previously applied shifts.

General Description

The various settings for Construction from Movement (SfM) Tool are described below...

Method

Method	Description
Dietrich	Camera backdrop are used to compute the field of view of each image. A bespeak is refraction corrected for the incidence angle of each paradigm for which it falls inside the field of view. The final correction to a point is the average of all corrections. This is the preferred and default method.
Small-scale Bending	This method makes the assumption that all incidence angles are at or near perpendicular with the water surface, or in other words that they are small angles of incidence. For a downwardly facing photographic camera with a horizontal field of view of seventy degrees the fault due to refraction is betwixt 25% and 32% of water depth. The default setting of i.34 for the refractive index of water volition account for betwixt 100% of the refraction error at nadir (near the camera rails) to 70% at the outer extents of the field of view (away from the photographic camera track). This will account for the majority of the refraction error but will leave some of the data in the outer extents of the field of view shoal biased at a maximum of 10% of water depth. For the aforementioned photographic camera configuration a calibration factor of one.48 will over-correct with 140% of the refraction fault at nadir to 100% at the outer extents of the field of view. This will deep bias the data near the camera runway upwards to 10% of water depth, but in some cases may be preferable for matching information at the edge of the aeriform survey with acoustic derived bathymetry in deeper waters. This method should be used if you do not have access to camera positions and orientations.

Water Surface

This group of settings relates to describing the water surface and it'southward properties.

H2o Height

This is the height of the water in your vertical datum used during data acquisition.

Case: If your information is referenced to hateful bounding main level (MSL) and the tide was one.0 meters beneath MSL during data acquisition so the water elevation should exist entered every bit -i.0 meters.

Refractive Index

This is the refractive alphabetize for water with respect to air.

This should mostly not be modified unless you lot are using the Small-scale Angle method and tin can take some deep biasing of the data.

Camera

These settings are merely applicable to the Dietrich method, and required.

Focal Length, Sensor Width, and Sensor Height should exist provided by the photographic camera manufacturer or accessible within your SfM processing software. All values should exist in millimeters.

These are used to compute the field of view of the camera.

Image Position/Orientation

These settings are only applicative to the Dietrich method, and required.

File

This is the "Omega Phi Kappa" file export from yous SfM software describing the paradigm, or camera positions and orientations.

You lot will accept to configure the ASCII parser for the 6 required fields: 10, Y, Z, Omega, Phi, and Kappa:

• 10, Y,  and Z are Easting, Northing, and Height, or Longitude, Latitude, and Height respectively
• Omega, Phi, and Kappa are the rotations about the 10, Y, and Z axes respectively

This is a photogrammetry specific convention and is dissimilar from our standard rotation conventions.

Coordinate Reference Organization

This should be the coordinate reference arrangement (CRS) of the positions in the file. This is required in order to relate the prototype positions with the project data.

The default is the projection CRS, which assumes there is no transformation required.

Starting from AgiSoft

Camera Properties

The photographic camera properties can exist establish in Agisoft past:

1. Tools Menu → Photographic camera Scale...

two. The focal length and the pixel size are shown below.

3. To become the sensor width and height, multiply the resolution by the pixel size.

Example:

Sensor Width/Height

5472 10 0.00239981 mm = 13.132 mm

3648 x0.00239981 mm = 8.755 mm

Camera Position & Orientation

The camera position & orientation can be found in Agisoft by:

1. Tools → Export → Export Cameras...

two. For "Save as type:" select "Omega Phi Kappa (*.txt)"

The Omega Phi Kappa (.txt) File Format must be configured to the correct ASCII Format, shown below.

Use As: --, 10, Y, Z, Omega, Phi, Kappa

After the offset import, Qimera should call up the previously used ASCII Format.

Starting from Pix4d

Photographic camera Properties

The photographic camera properties can be constitute in the project params file here:

<projection binder>\1_initial\params\<project name>_pix4d_calibrated_internal_camera_parameters.cam

OR

1. In the Pix4D awarding, the camera properties can be found by:

Projection → Image Backdrop Editor..

2. Selected Photographic camera Model → Edit...

three.The sensor width/height, and focal length are shown beneath.

Camera Position & Orientation

The camera position & orientation tin can be found in the project params file here:

<project folder>\1_initial\params\<project name>_calibrated_external_camera_parameters.txt

The calibrated_external_camera_parameters (.txt) File Format must exist configured to the correct ASCII Format, shown below.

Employ Equally: --, X, Y, Z, Omega, Phi, Kappa

After the first import, Qimera should remember the previously used ASCII Format.

Example: Small-scale Angle Method

1. Import Processed Indicate Files
2. Create Dynamic Surface
3. Optional: Create a Static Surface to be used for comparison after the correction

4. Select the Processed Point Files you desire to run the Structure from Motion (SfM) Bathymetry Correction on

5. Tools Menu → Utilities → SfM Correction...

6. Enter in H2o Height & Refractive Index

7. Click OK

8. Candy Point Files & Dynamic Surface volition update

ix. Optional: Compare the differences by creating a profile on the updated Dynamic Surface & original Static Surface

In this instance, the Blue line is the updated Dynamic Surface and the Green line is the original Static Surface.

Afterward running the Construction from Motion (SfM) tool, the surface is corrected and shifted, shown above in the Profile Dock.

Example: Dietrich Method

1. Import Candy Signal Files
2. Create Dynamic Surface
3. Optional: Create a Static Surface to exist used for comparison afterward the correction

iv. Select the Processed Point Files y'all want to run the Structure from Motion (SfM) Bathymetry Correction on

5. Tools Card → Utilities → SfM Correction...

6. Enter in Water Height, Refractive Index, Camera Parameters (Attainable in SfM processing software)

7. Import the Image Position/Orientation .txt file exported from the SfM processing software

8. Click Configure to check that the correct ASCII File Configuration is selected (–, X, Y, Z, Omega, Phi, Kappa)

ix. Check to ensure the Geodetics are right

ten. Click OK

12. Optional: Compare the differences by creating a profile on the updated Dynamic Surface & original Static Surface

In this case, the Blueish line is the updated Dynamic Surface and the Green line is the original Static Surface.

Later on running the Structure from Motion (SfM) tool, the surface is corrected and shifted, shown above in the Contour Dock.

Source: https://confluence.qps.nl/qimera/2.2/en/how-to-qimera-structure-from-motion-sfm-182618055.html

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