1Position-fixing or locating soundings
process of determining the horizontal position of a measured depth with respect to an established horizontal control system.
2Time Interval Along a Range Line
uses parallel range lines perpendicular to the shore baseline.
3Time Interval Along a Range Line
Soundings are taken at regular intervals, and the distance traveled between soundings is determined by proportioning time intervals.
4Time Interval Along a Range Line
particularly convenient when using continuous-reading echosounders, lead lines, or sounding rods.
5Range Line and an Angle from Shore
the vessel travels along a range line while a transit or theodolite at one end of the shore baseline measures the angle between the baseline and the boat's reference sight.
6bow or leadsman
the reference sight is usually directed toward the
7Connecting baselines
can be used when additional survey coverage is needed.
8Range Line and an Angle from Shore
particularly suitable for small lakes or areas with short range-line distances.
9Intersecting Range Lines
method in which the baselines and range lines intersect at approximately right angles.
10One Angle and Stadia Distance from Shore
uses an instrument positioned near water level, eliminating the need for vertical-angle corrections.
11d = Ks + C
Where:
• d — horizontal distance
• s — stadia interval
• K — 100
• C — 0
Stadia Formula
12One Angle and Stadia Distance from Shore
suitable for small bodies of water with calm currents.
13Cross Rope / Tag-Line Method
uses a calibrated wire rope marked with cross-section distances and stretched perpendicular to the shore baseline hubs across a stream.
14Secondary rope
may be used to secure the boat when the current is swift.
15Direction and Vertical Angle (Norwegian Method)
uses an instrument positioned on high ground to measure the vertical or depression angle down to the survey boat.
16Direction and Vertical Angle (Norwegian Method)
particularly useful where chaining across the water is impossible.
17Two Angles from Shore (Intersection Method)
uses two shore instrument stations.
18Two Angles from Boat (Resection / Three-Point Fix Method)
determines the boat's position by observing angles between three known shore control points.
19Sextant
typically used to measure the angles from the boat.
20Angle of intersection between the circumferences
determines the strength of the position fix.
21Strongest fix
occurs when the observer is inside the triangle formed by the three objects.
22Weak fix
occurs when the circles approach tangency.
23Case 1
the observer is inside the triangle formed by the three known objects.
24Case 2
the observer is outside the triangle but has a well-defined intersection geometry.
25Case 3
the observed geometry approaches tangency, producing a weak and less reliable position fix.