Function Description
A line M is a linear feature object composed of a set of points with X, Y coordinates and linear measurement values (M values). For example, highway milestones. Traffic management departments often use highway milestones to mark and manage road conditions, vehicle speed limits, and accident points on highways. Line M calibration is the process of adjusting route measurements to align with known reference points. For more information on route calibration, please refer to Calibrate the Route Overview.
Function Entry
- Edit Data tab -> Drop-down menu of the Feature Editing group -> Calibrate M Values.
Operation Instructions
- Add the route data to the map window, set the layer to an editable state, and select a line M that requires M value calibration.
- In the Edit Data tab, click the Calibrate M Values button from the Route Edit dropdown menu to open the Line M Calibration window.
- The list in the dialog displays the coordinates and M values of the line M nodes. Users can check the route nodes to use as reference points for M value calibration. Selected line M nodes will be highlighted on the map, and the M values of the reference points can be directly modified in the list.
- Set the calibration method in the parameters section. The calibration methods are divided into: Calibrate by Distance and Calibrate by Measure. For an introduction to these two calibration methods, please see the related content in Calibrate the Route Overview.
- Calibrate by Distance: Calculates M values based on reference points using the distance along the route between two points.
- Calibrate by Measure: Calibrates using the scale values corresponding to the positions of the reference points on the route. This method is particularly suitable for fine-tuning the scale values of a route when the ratio between the route length and the scale values is inconsistent.
- Ignore Gaps Between Subobjects: Sets whether to ignore intervals between subobjects. By default, intervals are ignored. A route can be a complex object containing multiple subobjects. Gaps occur when two subobjects are not continuous. Whether to ignore gaps between subobjects affects the continuity of route scale values. If gaps are ignored, the scale values will be continuous; otherwise, they will be discontinuous, and the distance of the gap between subobjects will be the Euclidean distance between the two endpoints.
As shown in the figure below, when ignoring gaps between subobjects, the M value of the endpoint of the first subobject is the same as the M value of the starting point of the second subobject. When not ignoring gaps, the M value of the starting point of the second subobject is the M value of the endpoint of the first subobject plus the Euclidean distance of the gap between them.
- After setting the above parameters, click the Calibrate button to execute the operation.
Notes:- At least two reference points are required for route calibration. It is recommended to use the two reference points closest to the node to be calibrated.
- If the M value of a reference point is null (i.e., -9999), the line M calibration will fail.
Related Topics