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4.2 Choosing an appropriate orientation
All projects are different, with their own set of unique challenges that need to be overcome. These challenges are
never the same, but the Merlin LT’s design offers the user several different scanning orientations which can provide
scan patterns appropriate for your specific survey application.
It is important to ensure that the mounting orientation of the Merlin LT unit is correct from the outset of any specific
project. Selecting the correct mounting angle will minimise shadows that cause gaps in the scan data and will ensure
the best coverage of the targeted area. This will avoid the need to run extra survey lines, reducing cost and time.
Some of the considerations to take into account when selecting the orientation of the Merlin LT include:
•
Range to the target from the vessel’s sailing line;
•
Angle of incidence of the laser with respect to the targeted surface;
•
Foreground obstructions;
•
The position, shape and orientation of the targeted objects or landscape.
Below are some recommendations that will help to assist in choosing the most appropriate mounting angle of the
Merlin LT system for your specific project. Note that some projects would benefit from using the optional mounting
plate which allows the Merlin LT to be mounted at fixed horizontal angles from the vessel’s centre line: see section
4.2.1 Example 1
When surveying features such as lampposts, telegraph poles, masts and marker posts along harbour walls or river
channels, it is advised to have the vertical angle set to 45°. This allows the laser scan pattern to ‘slice’ through the
vertical structure at an angle. A vertical angle of 90° could result in the feature being missed, as the ‘slice’ of data
would be very close to vertical, and therefore in the same plane as the target object.
4.2.2 Example 2
When carrying out DTM (Digital Terrain Model) work – such as beach profiling along a coastline or flood-plain
mapping along a canal or river – it is recommended to have the vertical angle set at 90° as this will give the greatest
range either side of the vessel.
4.2.3 Example 3
When surveying buildings or man-made structures along a harbour wall or river, it is recommended to mount the
Merlin LT unit at a 45° vertical angle, and to use the mounting plate to rotate the Merlin LT to a 22.5 or 45° horizontal
angle.
By rotating the Merlin LT around the horizontal axis, the laser can view the façades of buildings and structures that
run both perpendicular to and parallel with the direction of vessel travel.
