iTwin Capture Modeler Aerotriangulation Settings
Georeferencing options
General rules
· Adjustment constraint: To be selected for any constraint with a high level of accuracy (precise GPS: 5cm or better)
· Final rigid registration: Can only be use for data with a lower level of accuracy (floating or raw GPS: 10cm or above).
· If only one georeferencing source is available and can be used as Adjustment constraint (as in the photo positioning metadata in the above screenshot) it will also be used for the final scene registration in the aerotriangulation backend, so it is not necessary to check the Final rigid registration box.
When to use Adjustment constraints
· The data which is selected as adjustment constraint will be used for the AT intermediate stage of photo-matching. It therefore has the power to change the photos connections (tie-points) and warp the photo block.
· Any data which has a high level of accuracy (5cm or better) can be use the as adjustment constraint option
· Several constraints can be chosen, but the user has to make sure that these constraints are consistent with each other (no Z offset between photo metadata and GCP’s for instance) or it may cause the AT to fail.
When to use Final rigid registration
· The data which is selected to use Rigid registration will be used for the AT final step: georeferencing/scaling. It will only be used to ‘block-shift’ (translation, rotation, scale factor) the photo-block to the defined location but doesn’t have the ability to warp the block or modify the connections between photos
· Any georeferencing data can be used as a rigid constraint. Even a single control point to georeference the scene
· Only one data source can be used as Rigid registration constraint.
Georeferencing using control points
If control points are in use in a block, they will be set to use adjustment constraint by default as they usually have a high level of accuracy.
In the case of the user creating some approximate control points (doubtful data source, Google earth marker…), it is better to set them back to use the rigid constraint option.
Georeferencing using photo metadata
If the images have pose metadata (geotags or imported pose data), it will be set to use the Rigid constraint option by default, as most of the drones currently still have a ‘raw’ GPS.
If a RTK set was used or if the imported pose metadata comes with a high level of accuracy, it is recommended to change it to the Adjustment constraint option.
Georeferencing using laser scan point clouds
Using Adjustment constraint: if the user has imported an accurate LiDAR point cloud and wants to warp / modify the photoblock so it aligns as much as possible with the point cloud.
Using Final rigid registration: If the point cloud is noisy and has a low resolution it is better to use this option, so that it reduces the probability of losing some images.
Scaling using user tie-points and positioning constraints
The last option available is to scale the photoblock if no georeferenced data source is available
It can only be used for the final Rigid Registration and will only scale the data (no georeferencing)
Presets
iTwin Capture Modeler includes some Presets (low level settings) that control all aerotriangulation processing settings which can help to improve the results of the aerotriangulation under specific conditions. For a description of the different presets included with iTwin Capture Modeler and when they should be used see the following knowledge article: