Tie points

Note: Once a reconstruction is created in a block, the Tie points tab is read-only.

Tie points are 2D correspondences corresponding to a same physical point with unknown coordinate.

The survey tab manages only user tie point ie. tie point defined manually by the user. Note than ContextCapture can automatically generate a large number of automatic tie points during the aerotriangulation process. See Automatic Tie points.

Tie points can be added manually or can be imported. See also Importing tie points (on page 66).

Usage

Used during the aerotriangulation of a block, user tie points can improve aerotriangulation accuracy and help the aerotriangulation in case of large baseline and ambiguous pattern. In most cases, user tie points are not required, because ContextCapture can cope with using only automatically generated tie points. User tie points should be used only to solve aerotriangulation issues. In all cases, before acquiring user tie points, we recommend to run a first aerotriangulation.

Improve Photo position

Some repetitive elements in photos can cause a photo to not be properly positioned.

By defining points that represent the same position in different photos, you can guide the aerotriangulation process towards to correct photo positioning.

Group aerotriangulation components

Sometimes the aerotriangulation cannot connect all the photos due to a too large baseline or scale difference between some images.

With user tie points defined across the picture set, the multi-pass aerotriangulation mode is able to stitch the pictures together. To enable aerotriangulation multi-pass mode, from aerotriangulation settings, set "Component construction mode" to "Multi-pass".

At least 3 user tie points must be defined in 4 images (2 measures in each component that you want to fuse).

Note: Adding user tie points increases components connection chances, but the connection is never guaranteed

Add positioning constraints

Positioning constraints are priors based on user tie points to provide scene origin/scale/orientation. Positioning constraints are used to perform a rigid registration of the block during aerotriangulation.