The tie line tools within TerraMatch provide a flexible toolset with a wide range of capabilities for calibrating LIDAR data for both airborne laser scanners and mobile laser scanners. The kind of data you are working with will affect the desired settings and workflow. The best place to always start is with the TerraMatch User Guide, as it contains general information pertaining to workflow, and information about the parameters within the Tie Line Settings and Tie Line Search Settings.
Some tips to get started with Tie Lines:
- Define Tie Lines – Laser Data Settings
- Time gap should a min of 2 sec, but recommend it to be 10 sec to avoid small sections of points from a drive pass that exists in adjacent. This setting is only important if you would see the same location from data within the same flight line/drive pass, or from different channels and not using the “separate scanners” option.
- Max Error XY and Max Error Z should be the maximum observed error within the dataset.
- Fit tolerance should be set to the typical noise associated with shot to shot returns on a flat hard surface.
- Classes define which classes of points to be used for the various search tie line routines.
- Paint markings are only used when searching for paint markings, or interactively placing ground lines based on paint markings. The values should be set to one half of the min and one half of the max widths desired in order to better the placement of the marking in the centre of the paint stripe.
- Use search to find tie lines in flat ground or surface lines
- Direction: Slope, perpendicular and along movement options for optimizing tie line search depending upon scan pattern
- Length: Length of tie line observation. Should be 3-5 times nominal pulse spacing
- Depth: Profile width used by tie line. Should be approximately the nominal pulse spacing.
- Max Angle: Allowable angular deviation from average ground surface.
- Used mainly if there are insufficient “ground” features, use this search to find section lines along roof intersections
- Length: Length of tie line observation. Should be a range suitable for planar surface lengths found on the buildings.
- Min width: Minimum allowable width of a plane.
- Planarity: Allowable point deviations from the plane.
- Min Slope: Minimum slope of planes to be observed.
- Require # observations: Ensures more than one look observed at a feature for matching purposes.