Drifter Displacement Velocity Fixes Calculator
Signed segment velocities from actual common planar drifter fixes/time; not geodetic conversion or future trajectory.
Description
Calculate interval-average east and north velocities from timed local drifter fixes.
Successive drifter fixes in local Cartesian coordinates give interval-average displacement velocities. Each result belongs to the interval between two fixes, rather than an instantaneous observation.
When to use this tool
Calculate interval-average east and north velocities from timed local drifter fixes. Use it when the input measurements and conventions below match the operation you need.
- Prepare eastFixesM, northFixesM, timesSeconds, respecting the measurement basis and boundaries below.
- Compare the worked example with your intended operation before reusing its result.
How to use the tool and how it works
- Enter every field in the input table using the stated units and exact supported selector spelling where applicable.
- Run the tool. Correct input errors before interpreting an output.
- Read the result fields below; use accompanying flags and the stated sign, boundary or model convention when interpreting a number.
Supply aligned east-coordinate, north-coordinate and time lists with at least two entries and strictly increasing times. For each neighboring pair the tool divides the coordinate difference by elapsed time, returning one east and one north velocity per interval.1
| Input field | Meaning and units | Accepted input |
|---|---|---|
| eastFixesM | East fixes m. Meters. | List of finite numbers |
| northFixesM | North fixes m. Meters. | List of finite numbers |
| timesSeconds | Times seconds. Seconds. | List of finite numbers |
| Output field | Interpretation |
|---|---|
| result | Object containing the following named result fields. |
| result.eastVelocitiesMPerS | East velocities mper s list, in the ordering described in the calculation. |
| result.northVelocitiesMPerS | North velocities mper s list, in the ordering described in the calculation. |
{
"input": {
"eastFixesM": [
0,
10,
0
],
"northFixesM": [
0,
0,
10
],
"timesSeconds": [
0,
10,
20
]
},
"output": {
"result": {
"eastVelocitiesMPerS": [
1,
-1
],
"northVelocitiesMPerS": [
0,
1
]
}
}
}Limitations and assumptions
- Coordinates must share a local frame and compatible distance units. Latitude/longitude projection, measurement uncertainty, wind slip and attribution to ocean current are not handled.
- Every declared field is required and unexpected fields are rejected. Numeric inputs must be finite; input errors are distinct from a valid false result or an explicitly qualified output.
- Extremely large inputs and nonfinite or excessively large outputs are rejected. List positions reported by the tool use zero-based indices unless stated otherwise.
Alternative or Complementary methods
Compare the result with independently checked observations or a model that covers the omitted dynamics. Use compatible frames, units and sampling conventions when carrying the value into another calculation. Compare the scope of the nearby tools below before substituting one.
References
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