Field guide
Make chainage and offset traceable to a baseline segment
A coordinate, a station and a side only make sense when the baseline direction is clear.
Use a baseline that represents the intended route
This station offset calculator works with an ordered series of planar coordinates. It connects consecutive baseline vertices with straight segments and accumulates their horizontal lengths from the starting station you specify. You can then find stations and signed offsets for supplied coordinates, or generate coordinates from a list of stations and offsets. Each answer retains a segment number and a source row, so the result can be traced back to the geometry that produced it.
The order of the baseline is a design input. A point file sorted by point number, elevation or easting may describe a very different route from the intended alignment. Prepare the vertices in travel order before importing them. The tool does not sort points or infer connections from their proximity. A repeated coordinate at consecutive rows creates a zero-length segment and blocks the baseline; it is not silently removed. Nonconsecutive repetitions remain meaningful geometry and may lead to more than one candidate.
Choose the calculation direction and map the fields
In coordinates-to-station mode, map the target easting and northing columns. The calculator projects each target perpendicularly onto every baseline segment and keeps projections whose feet fall within that segment. It reports the station at the foot, the distance along the segment, the signed perpendicular offset and the foot coordinates. A target beyond every eligible segment produces an outside result. The tool does not extend the first or last segment, and it does not substitute a nearest endpoint distance for a perpendicular offset.
In station-to-coordinates mode, map a station column and a signed offset column instead. The station determines the position along the baseline; the offset moves perpendicular to the chosen segment. Offset entries are ordinary signed distances, even when station entries use a plus notation. The baseline always uses easting and northing columns. Column numbers in the interface start at one, while zero in the ID field means to identify requests by their original row. Extra fields are retained in the JSON report.
Keep station notation separate from distance units
A start station is a label offset for cumulative distance. Starting at 1000 does not move the first vertex or change the shape of the route. A segment of length 30 then ends at station 1030. The plain format accepts that value directly. The three-digit format accepts 1+030 or K1+030, while the two-digit format expresses the same value as 10+30. Choose one convention for the calculation; the parser does not guess the meaning of a plus sign or mix formats within the request list.
All coordinates, stations and offsets must use the same length unit. The unit selector records metres, international feet or US survey feet without transforming the values. A three-digit station format does not automatically mean metres. The station value and formatted display are separate result fields. Rounding the display can carry a value into the next displayed station, so use the numerical field when comparing close positions. A negative sign applies to the whole station, such as -0+050 representing minus fifty in the three-digit format.
Read right and left in the baseline direction
Offsets are positive on the right and negative on the left when looking along increasing station. On an eastbound segment, a point south of the line has a positive offset. On a northbound segment, a point east of the line has a positive offset. A point on the segment has zero offset. These simple checks help reveal reversed coordinate columns or a baseline entered in the wrong direction before a large batch is accepted.
The reverse-baseline option reverses vertex order and recalculates all cumulative distances from the start station currently entered. It also reverses the meaning of left and right. It does not preserve the original station labels while merely changing the display direction. If the reversed route must start at a different station, enter that value explicitly. Keep the reference field descriptive enough to identify the baseline revision, coordinate system and direction used in the handoff.
Resolve multiple candidates rather than assuming the nearest one
A bent, overlapping or returning baseline can admit several perpendicular projections for the same target. Each projection may produce a different station and offset. The candidate report lists them all, including the segment and foot coordinates. A shorter perpendicular distance is useful evidence, but it cannot establish which branch of an alignment the point belongs to. The interface therefore leaves a multiple-candidate row unresolved until you choose the intended segment.
There is a related ambiguity in the other direction. At an interior vertex, the incoming and outgoing segments share a station but have different perpendicular directions. A nonzero offset can therefore generate two different coordinates. Review the candidate table and select the segment whose normal matches the task. Even a zero-offset corner retains both segment references for clarity. The overview is a review aid; the source row and candidate table are the detailed record. Point export remains locked until every request is resolved and you apply the reviewed selections.
Check a short example by hand
Consider a synthetic baseline with A at E0 N0, B at E30 N0 and C at E30 N40, starting at station zero. The first segment has length 30 and the second has length 40, giving cumulative vertex stations 0, 30 and 70. A target at E10 N-5 projects onto the first segment at station 10 with offset +5. A target at E35 N20 projects onto the second segment at station 50 with offset +5. These are calculation examples, not field observations.
Now place a target at E25 N5. It has a projection on the first segment at station 25 with offset -5, and another on the second at station 35 with offset -5. Neither answer alone identifies the intended segment. For the forward calculation, station 30 with offset +5 produces E30 N-5 using segment one and E35 N0 using segment two. Selecting the correct segment resolves the construction. Reversing the baseline changes the first example target to station 60 and offset -5 when the new start station is zero.
Prepare imports and retain failed records
Upload a UTF-8 CSV or TXT file, or paste the same content into the text area. Select comma, semicolon or tab explicitly and confirm whether the first record is a header. Quoted fields may contain separators, and the report retains original source lines and additional columns. Duplicate IDs are not merged: two rows with the same name remain two separate requests. Blank lines are ignored, while a missing coordinate or offset within a nonblank record is reported as invalid rather than being treated as zero. XLSX workbooks are also accepted for this input: explicitly choose the worksheet, and replace formulas, dates or error cells with plain values before importing.
The baseline must be valid as a whole because skipping a vertex would change the route. Invalid target rows are retained beside successful results with their reasons. Outside stations and projections are also retained. Correct those requests in the original text and calculate again before applying a point set. Input edits invalidate the current result, preventing an old export from being mistaken for a new calculation. The restore control retrieves the last calculation inputs; clearing a session removes local working data without changing your source files.
Choose the export that matches the handoff
The full candidate CSV is an audit table. It includes all target records, every candidate, a selection flag, source identity and numeric station and offset fields. It is available before applying so unresolved work can be reviewed elsewhere. The JSON report also preserves the raw input text, mappings, baseline vertices, cumulative stations, choices, units, reference, calculation version and time. These reports explain how the result was produced; a point list alone does not carry the same context.
The point CSV becomes available after every row is resolved and the choices are applied. It contains the selected easting and northing, the original request ID, source row, segment, station and offset. Elevation is blank because this tool performs a two-dimensional calculation. In inverse mode the point coordinates are the original target coordinates; foot coordinates remain in the candidate report. Point CSV preserves IDs verbatim for downstream surveying tools, so import ID and text columns as text in spreadsheet software. You can also transfer the applied file locally to the point checker for another field review.
Understand numerical and geometric limits
Use projected or local Cartesian coordinates with consistent axes, not latitude and longitude degrees. This calculator does not transform coordinate systems, calculate geodesic distances, fit curves, apply station equations or model transitions and vertical alignment. Representing a curved design with straight chords changes its geometry and chainage. If the task requires the actual curve, use a method that supports those design elements rather than treating this polyline result as equivalent.
Calculation runs in a local worker and can be cancelled. A baseline may contain two to one thousand vertices, with up to ten thousand requests, one million segment/request pairs and fifty thousand stored candidates. Each text input and CSV export is limited to ten MiB. Inputs support magnitudes up to one trillion and up to thirty-six decimal places; calculated lengths and station magnitudes are also bounded. Exact decimal products determine projection membership and side, while square roots and normalized directions have finite floating-point precision. Extra output digits do not guarantee field accuracy. Review an independent example and the relevant segment choices before using the result.