getSegmentstartD

getSegmentstartD is a function used in segmentation-oriented software libraries to obtain the starting coordinate of a segment along a specified dimension D. In typical implementations, a segment represents a contiguous region within a dataset or signal, and D indicates the dimension along which the start is measured, such as an axis in a multi-dimensional array or a coordinate axis in a time series.

The function accepts two arguments: segment and D. The segment is an object or record that defines the segment boundaries, commonly exposing properties such as start and end indices or coordinates. D may be an integer index or a string key corresponding to the target dimension.

Return value: a numeric coordinate or index representing the start position of the given segment along dimension D. If the segment does not have a defined start along D, or D is invalid, implementations may throw an error or return a null/NaN value.

Behavior notes: In systems using inclusive start semantics, the result corresponds to the first element of the segment along D. In some libraries, segments may be defined in terms of half-open intervals; consult the API for precise semantics.

Examples: getSegmentstartD(seg, 'x') returns seg.start.x; getSegmentstartD({start: [5, 10], end: [9, 15]}, 0) returns 5.

Performance: The call typically runs in O(1) time, assuming access to precomputed boundary properties.

See also: getSegmentendD, getSegmentlength, Segment, segmentation APIs.

History: Common in modern data analysis and graphics libraries; exact signature varies by language.