docs: remove misleading 'epoch' terminology from SetBaseline/GetBaseline XML comments

Agent-Logs-Url: https://github.com/petesramek/polyline-algorithm-csharp/sessions/14462e5e-f3ab-4b1a-aabf-b61049ff1191

Co-authored-by: petesramek <2333452+petesramek@users.noreply.github.com>

Author: Copilot

src/PolylineAlgorithm/Abstraction/IPolylineFormatter.cs

@@ -29,8 +29,9 @@ public interface IPolylineFormatter<TCoordinate, TPolyline> {
     int Width { get; }
 
     /// <summary>
-    /// Returns the baseline (epoch) for the column at <paramref name="index"/>, or <c>0</c> if none is configured.
-    /// The encoder subtracts this value from the first item's scaled column value to keep the initial delta small.
+    /// Returns the baseline for the column at <paramref name="index"/>, or <c>0</c> if none is configured.
+    /// The encoder uses this as the starting point for the first item's delta computation: the initial
+    /// delta for the column is <c>scaled_first_value − baseline</c> rather than <c>scaled_first_value</c>.
     /// </summary>
     /// <param name="index">The zero-based column index. Must be in the range <c>[0, <see cref="Width"/>)</c>.</param>
     /// <returns>The baseline value, or <c>0</c> when no baseline has been defined for the column.</returns>

src/PolylineAlgorithm/FormatterBuilder.cs

@@ -17,7 +17,7 @@ namespace PolylineAlgorithm;
 /// <remarks>
 /// <para>
 /// Use <see cref="Create"/> to obtain an instance, call <see cref="AddValue"/> once per column,
-/// optionally chain <see cref="SetBaseline"/> to specify an epoch for the most-recently added column,
+/// optionally chain <see cref="SetBaseline"/> to set a reference baseline for the most-recently added column,
 /// optionally chain <see cref="WithCreate"/> to register a factory for the decoding direction,
 /// call <see cref="ForPolyline"/> to supply the polyline surface delegates (required), then call
 /// <see cref="Build"/> to produce the immutable <see cref="PolylineFormatter{TCoordinate, TPolyline}"/>.
@@ -87,11 +87,17 @@ public FormatterBuilder<TCoordinate, TPolyline> AddValue(string name, Func<TCoor
     }
 
     /// <summary>
-    /// Sets a baseline (epoch) on the most-recently added column.
-    /// During encoding the baseline is subtracted from the first item's scaled column value,
-    /// keeping the initial delta small when the absolute first value is large.
+    /// Sets a reference value (baseline) on the most-recently added column.
+    /// During encoding, the baseline is subtracted from the first item's scaled column value so that
+    /// the initial delta is <c>scaled_first_value − baseline</c> rather than <c>scaled_first_value</c>.
+    /// Use this when the absolute scaled value of the first data point for a column would otherwise
+    /// produce a very large initial encoded delta.
     /// </summary>
-    /// <param name="baseline">The baseline value to apply to the first item's column value.</param>
+    /// <param name="baseline">
+    /// The reference value to subtract from the first item's scaled column value during encoding.
+    /// The decoder automatically adds this value back, so the reconstructed item matches the
+    /// original input.
+    /// </param>
     /// <returns>The current builder instance for method chaining.</returns>
     /// <exception cref="InvalidOperationException">
     /// Thrown when no rules have been added yet. Call <see cref="AddValue"/> before

src/PolylineAlgorithm/Internal/FormatterRule.cs

@@ -40,8 +40,9 @@ internal FormatterRule(string name, long factor, Func<T, double> select, long? b
     internal long Factor { get; }
 
     /// <summary>
-    /// Gets the optional baseline (epoch). When set, the encoder subtracts this value from the
-    /// first point's scaled column value to keep the initial delta small.
+    /// Gets the optional reference value used as the baseline for the first encoded point.
+    /// When set, the encoder subtracts this value from the first item's scaled column value so that
+    /// the initial delta is <c>scaled_first_value − baseline</c> rather than <c>scaled_first_value</c>.
     /// </summary>
     internal long? Baseline { get; }