PhotoMesh provides three types of control points:
- Ground control points (GCP) – Improve the accuracy of the model’s position by associating real-world X, Y, Z coordinates (generally obtained through surveying or sampling methods) with corresponding locations (in pixels) in photos. In order to enable your control points to be fully utilized in the AT process, it is recommended to add at least 3-5 control points per AT tile. When only two control points are provided, simple vertical adjustment, scaling and rotation are performed. When only one control point is provided, only vertical adjustment is performed.
- Check points – Ground control points that do not affect the AT calculation and are only used to sample the AT accuracy in the result. The point is included in the build report and shows calculated errors for accuracy validation purposes.
- Tie points – Establish a correspondence between project photos and improve aerotriangulation results through identification of the same physical point in three or more photos. The XYZ position of the physical point is not necessarily known. Generally, it is recommended to run an initial aerotriangulation to identify photos that either weren’t calculated in AT or that have high median errors, as well as areas of insufficient matches between groups of photos.
Control points are marked in photos using the Control Point Editor. In addition to the ribbon, the Control Point Editor includes a photo viewing window, a photos panel, a control point table, and a sampled photos panel - that gradually becomes populated with photo thumbnails as you mark the control point in photos. The photos panel displays the photos from which to select the photos for marking control points, either as thumbnails or in table format with relevant photo information.
Marking and Auto-Marking Control Points in Photos
Control points are marked in photos using the Control Point Editor. Each control point should be marked in a few photos from each collection or photo direction. It is recommended to mark at least 10 photos for each control point.
In addition to the ribbon, the Control Point Editor includes:
- A photo viewing window
- A photos panel, which displays available photos as thumbnails or in table format with relevant information
- A sampled photos panel that is gradually populated with thumbnails as you mark the control point in photos.
Note: In order to enable your ground control points to be fully utilized in the AT process, it is recommended to add at least 3-5 ground control points per AT tile:
- 1 control point – Only vertical adjustment is performed
- 2 control points - Vertical adjustment, scaling, and rotation are performed
- 3+ control points - Full transformation
Any control point marked in fewer than three photos will be marked in red in the Control Point list.
Auto-Marking Based on Control Point Marker Patterns: If your photos include control point marker patterns (e.g., checkerboard or cross patterns), PhotoMesh can automatically identify them and mark control points in photos based on them. It searches the photos for the chosen marker type based on the selected template, and links each detection to the nearest control point. If the marker includes an identifier, PhotoMesh will associate it with a specific control point instead.
If you manually mark a photo after enabling auto-marking, your manual marking takes precedence and overrides the automatic process for that control point. Automatically detected markers are added as regular markers only after aerotriangulation is performed. It is recommended to review the photos in Control Point Editor after performing aerotriangulation to see which were auto-marked with control points, so that you can add manual markers, if necessary.
Auto-Detect Based on First Manual Marking: After you manually mark a control point in a photo, PhotoMesh can auto-detect this control point in other photos. PhotoMesh scans up to 100 nearby photos, prioritized by proximity to the control point, and stops when it reaches the defined Maximum Detect Photos limit. Only photos with a confidence score of 98% or higher are considered, and previously marked photos are skipped in repeated runs.
This feature can be enabled globally through the PhotoMesh Options, triggering the search automatically after the first marking of each control point, or activated manually for individual control points through the Control Point Editor.
Auto-Marking Photos: If your photos include control point markers, PhotoMesh can automatically identify them and mark control points in photos based on them. You can select the template that corresponds to your marker type, e.g., checkboard or cross. After selecting a control point for auto-marking, this setting can be overridden by manually marking this control point in one or more photos. The automatic markers are added as regular markers to the photos only after aerotriangulation is performed.
More about: Using control points >