Field guide
A practical guide to a traceable calculation
Define the input and assumptions, then review the result and delivery format.
Start with a line that has a known order
This offset coordinates calculator builds a parallel reference line from an ordered set of planar coordinates. It accepts a straight line or an open polyline made from straight segments. Upload a CSV or text file, confirm its columns, select left or right, and enter a positive perpendicular distance. The output contains a corresponding offset vertex for each accepted source vertex, together with source segment information and a report of any geometry that prevents delivery.
A point list does not automatically define a route. Arrange the source rows in the intended forward order before importing them. The page connects consecutive rows exactly as supplied; it does not sort by point number or guess a centreline from scattered observations. Keep the original file separately so that another reviewer can reconstruct which order was used. Extra source fields remain in the JSON report even though only E and N are used for the planar calculation.
Map coordinate meanings before calculating
Choose the delimiter and state whether the first row is a header. Column numbers in the interface start at one. Map easting to E and northing to N, regardless of whether the source calls them X and Y. The ID column can be set to zero to identify vertices by source row instead. A malformed record blocks calculation rather than being skipped, because removing a vertex could change the entire route and its offset.
Use one planar coordinate system and one length unit throughout. Metres, feet, and US survey feet are labels for already consistent inputs, not automatic conversions. Geographic longitude and latitude are outside this tool's domain. Describe the baseline, drawing revision, and coordinate system in the reference field, then confirm the assumptions. If the file represents a curve sampled into short chords, the result offsets those straight chords, not the original analytic curve.
Choose a side while looking forward
Left and right are defined while travelling through the vertices in row order. On a line heading north, its right side is east. On a line heading east, its right side is south. Reversing the row order changes this interpretation. A useful check is to select one simple segment with an obvious direction and verify that the preview puts the candidate line on the intended side before considering any corner details.
Enter the offset as a positive distance and choose the side separately. The engine shifts each supporting segment along its own perpendicular unit normal. That is why applying a fixed easting change to every vertex is not a general solution: a bent route has different normals along its different segments. A translation moves the complete shape in one fixed direction. A parallel offset keeps the requested perpendicular relationship to each source segment and then resolves how adjacent segments meet.
Understand the corner rule
This version uses miter joins. At an ordinary corner, the neighbouring shifted supporting lines are extended or trimmed to their intersection. Straight continuations keep the same normal shift. Endpoints move perpendicular to their single adjoining segment, with no additional extension beyond the source endpoint. The audit identifies endpoints, straight joins, ordinary miters, and blocked corners so that the result is not just an unexplained coordinate list.
The miter limit is the distance from the original corner to its candidate intersection divided by the requested offset. It is dimensionless and must be between one and one hundred. A square corner has a ratio of approximately 1.414214. A tight reversal can produce a very long miter even with a modest offset. If the ratio exceeds the selected limit, the page blocks point and DXF export and identifies the corner. It does not silently replace that corner with a bevel or rounded join.
Review topology before exporting
The checks cover consecutive duplicate coordinates, exact backtracking, a repeated closing endpoint, and contact or crossing between nonadjacent source segments. After computing the candidate line, the tool checks whether a segment collapses or reverses and whether nonadjacent output segments touch or intersect. An excessive inward offset can consume a short segment completely. A route can therefore be valid at one offset distance and invalid at a larger distance.
When any of these checks fails, the audit and JSON report remain available for diagnosis, but the point file and DXF stay blocked. The tool does not delete a loop, remove a troublesome vertex, or choose one of several possible repaired shapes. Review the source or select another distance, then calculate again. Issue lists are bounded for responsiveness; seeing a reported issue already means the result is not approved for delivery, even if there are more interactions elsewhere in the line.
Use a small benchmark before a production file
The built-in synthetic example has A at E0 N0, B at E30 N0, and C at E30 N40. A right offset of five produces E0 N-5, E35 N-5, and E35 N40. The corner moves diagonally because it is the intersection of the shifted eastbound and northbound segments. A left offset instead trims the inside corner to E25 N5. These values provide an easy check of side, axis order, and miter behaviour.
For your own file, independently calculate the perpendicular distance from both endpoints of a generated segment to its original supporting line. That distance should match the requested magnitude on the chosen side. Also review the first and last endpoints, because an offset does not automatically extend a route to a boundary or another feature. A successful numerical check does not establish whether the source line is the correct design alignment; that is why the reference field and original records are retained.
Inspect the plan and the complete audit
The plan uses equal scale with north up and east right. Blue markers identify original vertices, while amber markers identify offset candidates. Clicking a marker or using the arrow keys selects its source vertex and corresponding candidate. Local coordinate differences are used for plotting, so a large survey origin does not obscure a small offset. The picture has no basemap and cannot confirm that the coordinates use the intended real-world reference frame.
The vertex table is paginated, but its CSV and JSON exports contain the complete accepted input and calculation. The segment table gives each source length and chosen unit normal. A blocked candidate may still appear as diagnostic geometry in the plan; the summary and issue table decide whether delivery is enabled. Editing a file, mapping, distance, side, limit, or reference invalidates the prior preview and disables exports until the new result is calculated and approved.
Deliver coordinates and a supported CAD line
After valid geometry is reviewed, approve the preview to enable a point CSV and a two-dimensional DXF R12 file. The point file uses generated identifiers OFF-1, OFF-2 and so on, with Easting, Northing, blank Elevation, and a source-vertex description. Original identifiers, physical source lines, and coordinate values remain in the audit. Generated identifiers avoid silently merging vertices that happen to share the same original point label.
The DXF contains ordinary POINT entities and one open POLYLINE. Its XY geometry is encoded with Z equal to zero because the export is two dimensional; that zero is not an inferred design elevation. The separate point CSV keeps the missing height blank. No curve bulges, closed polygon, holes, labels, surfaces, or automatic vertical offsets are created. Confirm the selected length unit when opening the file in your receiving CAD application.
Work within explicit limits
The tool accepts two to one thousand ordered vertices and ten mebibytes of UTF-8 text. Coordinate values are limited to magnitude one trillion and up to thirty-six decimal places; distance and miter-limit inputs allow twelve decimal places. Computed directions involve floating-point normalization, so extra output digits are not a guarantee of field accuracy. The miter and intersection checks reduce common geometric mistakes without replacing design review.
Processing happens locally in a worker. Cancel preserves the input, restore last inputs retrieves the previous successful scenario, and clear session removes the working text and results without overwriting the original disk file. Keep the calculation report alongside the exported geometry. If your task needs a closed polygon buffer, a rounded corner, a transition curve, or automatic loop removal, choose a workflow that explicitly supports that geometry instead of treating this open-line result as equivalent.