Densify Geodesic Features

Overview

The Densify Geodesic Features tool performs geodesic densification on line features and multipart line features. It inserts intermediate points between adjacent original vertices based on the specified maximum segment distance, so the output line features better follow the true path on the Earth's ellipsoid.

This tool is suitable for line features that span large areas, such as flight routes, pipelines, boundary lines, and survey lines. Unlike ordinary planar densification, this tool first performs ellipsoidal calculations in the geographic coordinate system EPSG:4326, then converts the result back to the original coordinate system of the input features.

How It Works

The tool reads adjacent vertices of each input line feature segment by segment and calculates the surface distance between the two points. If the distance is greater than Maximum segment distance, the number of resulting segments is determined by the following formula:

$$n = \left\lceil \frac{L}{d} \right\rceil$$

Where $L$ is the surface distance of the current original segment, $d$ is the maximum segment distance set by the user, and $n$ is the number of segments after splitting. The tool calculates intermediate points at $d, 2d, 3d, \ldots$ until the original segment is split into multiple shorter segments.

Calculation method provides two path models:

• geodesic: A geodesic, or the shortest path between two points on the ellipsoid. This is suitable for most long-distance spatial analysis.
• rhumb: A rhumb line, or a route that maintains a constant azimuth. This is commonly used in nautical and aeronautical mapping where a constant heading must be represented.

The output features preserve the attribute fields of the input features, but the number of geometry vertices increases. The current implementation only processes LineString and MultiLineString geometries. Point or polygon inputs are treated as unsupported geometry types.

Use Cases

• More accurately represent ellipsoidal paths for cross-region line features, such as long-distance flight routes, submarine pipelines, and national boundaries.
• Reduce projection deformation of long straight segments before subsequent processing such as projection, clipping, overlay, or buffer operations.
• Convert coarse polylines into denser cartographic lines to improve map rendering and curve display.
• Control the spacing between adjacent vertices by maximum surface distance for later segment-based sampling or segmented statistics.

Parameters

Parameter	Description	Notes
Input vector file	The line features to densify.	Required. Supports line features and multipart line features.
Maximum segment distance	The maximum surface distance allowed for a single segment in the output line features.	Required. Default value: 1000.
Distance unit	The unit of Maximum segment distance.	Required. Default value: meters. Options: meters, kilometers.
Calculation method	The ellipsoidal path model used to insert points.	Required. Default value: geodesic. Options: geodesic, rhumb.
Earth radius	The semi-major axis of the reference ellipsoid.	Required. Unit: meters. Default value: 6378137.0, corresponding to the WGS84 semi-major axis.
Earth flattening	The inverse flattening of the reference ellipsoid.	Required. Default value: 298.257223563, corresponding to the WGS84 inverse flattening.
Output vector file	The densified line feature dataset.	Required. Preserves input attributes; output geometries contain more vertices.

Output

The output is a new line feature dataset. The start point and end point of each line feature remain unchanged, the original vertices are preserved, and additional vertices are inserted between them based on the specified distance threshold. If the input features have a defined coordinate system, the tool converts the output geometry back to the original coordinate system of the input features after calculation.

important

This tool uses ellipsoidal calculations, but the distance threshold is not in output coordinate system units. It is in meters or kilometers as specified by the Distance unit parameter.

Steps

1. Start the tool: Open the Geoprocessing Toolbox toolbox, go to Vector Tools > Feature Processing > Build, and open the Densify Geodesic Features tool pane.
2. Set the input: In Input vector file, select the line feature dataset to densify.
3. Set the distance threshold: In Maximum segment distance, enter the maximum allowed segment length, and select meters or kilometers in Distance unit.
4. Choose the calculation method: For most long-distance shortest paths, choose Geodesic. When a constant heading must be represented, choose Rhumb line.
5. Confirm ellipsoid parameters: The default parameters are WGS84 and usually do not need to be changed. If the business data explicitly uses another reference ellipsoid, enter the semi-major axis and inverse flattening according to the project requirements.
6. Set the output: Specify the path and name for Output vector file.
7. Run and check the result: Click Run. After the tool finishes, check whether the vertex density, spatial position, and attribute fields of the line features meet expectations.

Notes

• Input features must be line features or multipart line features. Point and polygon features are not applicable to this tool.
• The smaller the maximum segment distance, the more vertices the output contains, and the higher the processing and rendering cost.
• The current calculation uses two-dimensional longitude and latitude coordinates for point insertion. Three-dimensional Z values do not participate in geodesic interpolation.
• If the input features do not have a defined coordinate system, the tool still performs ellipsoidal calculations by interpreting coordinates as longitude and latitude. It is recommended to correctly define the coordinate system first.
• If you only need to insert points in a projected plane by coordinate units, use a planar densification tool instead of this geodesic tool.