WIP: Add Figure.scalebar to plot a scale bar on maps

doc/api/index.rst

@@ -31,6 +31,7 @@ Plotting map elements
     Figure.inset
     Figure.legend
     Figure.logo
+    Figure.scalebar
     Figure.solar
     Figure.text
     Figure.timestamp

pygmt/figure.py

@@ -449,6 +449,7 @@ def _repr_html_(self) -> str:
         plot3d,
         psconvert,
         rose,
+        scalebar,
         set_panel,
         shift_origin,
         solar,

pygmt/src/__init__.py

@@ -43,6 +43,7 @@
 from pygmt.src.project import project
 from pygmt.src.psconvert import psconvert
 from pygmt.src.rose import rose
+from pygmt.src.scalebar import scalebar
 from pygmt.src.select import select
 from pygmt.src.shift_origin import shift_origin
 from pygmt.src.solar import solar

pygmt/src/scalebar.py

@@ -0,0 +1,186 @@
+"""
+scalebar - Add a scale bar.
+"""
+
+from collections.abc import Sequence
+from typing import Literal
+
+from pygmt._typing import AnchorCode
+from pygmt.alias import Alias, AliasSystem
+from pygmt.clib import Session
+from pygmt.exceptions import GMTInvalidInputError
+from pygmt.helpers import build_arg_list
+from pygmt.params import Box
+
+
+def scalebar(  # noqa: PLR0913
+    self,
+    position: Sequence[float | str] | AnchorCode | None = None,
+    position_type: Literal[
+        "mapcoords", "boxcoords", "plotcoords", "inside", "outside"
+    ] = "plotcoords",
+    anchor: AnchorCode | None = None,
+    anchor_offset: Sequence[float | str] | None = None,
+    length: float | str | None = None,
+    label_alignment: Literal["left", "right", "top", "bottom"] | None = None,
+    scale_position: float | tuple[float, float] | bool = False,
+    label: str | bool = False,
+    fancy: bool = False,
+    unit: bool = False,
+    vertical: bool = False,
+    box: Box | bool = False,
+    perspective: str | bool = False,
+    verbose: Literal["quiet", "error", "warning", "timing", "info", "compat", "debug"]
+    | bool = False,
+    transparency: float | None = None,
+):
+    """
+    Add a scale bar on the map.
+
+    The scale bar is plotted at the location defined by the reference point (specified
+    by the **position** and *position_type** parameters) and anchor point (specified by
+    the **anchor** and **anchor_offset** parameters). Refer to
+    :doc:`/techref/reference_anchor_points` for details about the positioning.
+
+    Parameters
+    ----------
+    position/position_type
+        Specify the reference point on the map for the directional rose. The reference
+        point can be specified in five different ways, which is selected by the
+        **position_type** parameter. The actual reference point is then given by the
+        coordinates or code specified by the **position** parameter.
+
+        The **position_type** parameter can be one of the following:
+
+        - ``"mapcoords"``: **position** is given as (*longitude*, *latitude*) in map
+          coordinates.
+        - ``"boxcoords"``: **position** is given as (*nx*, *ny*) in normalized
+          coordinates, i.e., fractional coordinates between 0 and 1 in both the x and y
+          directions. For example, (0, 0) is the lower-left corner and (1, 1) is the
+          upper-right corner of the plot bounding box.
+        - ``"plotcoords"``: **position** is given as (x, y) in plot coordinates, i.e.,
+          the distances in inches, centimeters, or points from the lower left plot
+          origin.
+        - ``"inside"`` or ``"outside"``: **position** is one of the nine
+          :doc:`2-character justification codes </techref/justification_codes>`, meaning
+          placing the reference point at specific locations, either inside or outside
+          the plot bounding box.
+    anchor
+        Anchor point of the directional rose, specified by one of the
+        :doc:`2-character justification codes </techref/justification_codes>`.
+        The default value depends on the **position_type** parameter.
+
+        - ``position_type="inside"``: **anchor** defaults to the same as **position**.
+        - ``position_type="outside"``: **anchor** defaults to the mirror opposite of
+          **position**.
+        - Otherwise, **anchor** defaults to ``"MC"`` (middle center).
+    anchor_offset
+        *offset* or (*offset_x*, *offset_y*).
+        Offset the anchor point by *offset_x* and *offset_y*. If a single value *offset*
+        is given, *offset_y* = *offset_x* = *offset*.
+    length
+        Length of the scale bar in km. You can append different units to the length,
+        which are:
+        - **e**: meters
+        - **f**: feet
+        - **k**: kilometers
+        - **M**: statute mile
+        - **n**: nautical miles
+        - **u**: US Survey foot
+    scale_position
+        Specify the location where on a geographic map the scale applies. It can be:
+
+        - *slat*: Map scale is calculated for latitude *slat*
+        - (*slon*, *slat*): Map scale is calculated for latitude *slat* and longitude
+          *slon*, which is useful for oblique projections.
+        - ``True``: Map scale is calculated for the middle of the map.
+        - ``False``: Default to the location of the reference point.
+    label
+        Text string to use as the scale bar label. If ``False``, no label is drawn. If
+        ``True``, the distance unit provided in the **length** parameter (default is km)
+        is used as the label. The parameter requires ``fancy=True``.
+    label_alignment
+        Alignment of the scale bar label. Choose from "left", "right", "top", or
+        "bottom". [Default is "top"].
+    fancy
+        If ``True``, draw a “fancy” scale bar. A fancy scale bar is a segmented bar with
+        alternating black and white rectangles. If ``False``, draw a plain scale bar.
+    unit
+        If ``True``, append the unit to all distance annotations along the scale. For a
+        plain scale, this will instead select the unit to be appended to the distance
+        length. The unit is determined from the suffix in the **length** or defaults to
+        km.
+    vertical
+        If ``True``, plot a vertical rather than a horizontal Cartesian scale.
+    box
+        Draw a background box behind the directional rose. If set to ``True``, a simple
+        rectangular box is drawn using :gmt-term:`MAP_FRAME_PEN`. To customize the box
+        appearance, pass a :class:`pygmt.params.Box` object to control style, fill, pen,
+        and other box properties.
+    {perspective}
+    {verbose}
+    {transparency}
+
+    Examples
+    --------
+    >>> import pygmt
+    >>> from pygmt.params import Box
+    >>> fig = pygmt.Figure()
+    >>> fig.basemap(region=[0, 80, -30, 30], projection="M10c", frame=True)
+    >>> fig.scalebar(
+    ...     position=(10, 10),
+    ...     position_type="mapcoords",
+    ...     length=1000,
+    ...     fancy=True,
+    ...     label="Scale",
+    ...     unit=True,
+    ... )
+    >>> fig.show()
+    """
+    self._preprocess()
+
+    if position is None:
+        msg = "Parameter 'position' must be specified."
+        raise GMTInvalidInputError(msg)
+    if length is None:
+        msg = "Parameter 'length' must be specified."
+        raise GMTInvalidInputError(msg)
+
+    aliasdict = AliasSystem(
+        F=Alias(box, name="box"),
+        L=[
+            Alias(
+                position_type,
+                name="position_type",
+                mapping={
+                    "mapcoords": "g",
+                    "boxcoords": "n",
+                    "plotcoords": "x",
+                    "inside": "j",
+                    "outside": "J",
+                },
+            ),
+            Alias(position, name="position", sep="/", size=2),
+            Alias(anchor, name="justify", prefix="+j"),
+            Alias(anchor_offset, name="anchor_offset", prefix="+o", sep="/", size=2),
+            Alias(length, name="length", prefix="+w"),
+            Alias(
+                label_alignment,
+                name="label_alignment",
+                prefix="+a",
+                mapping={"left": "l", "right": "r", "top": "t", "bottom": "b"},
+            ),
+            Alias(scale_position, name="scale_position", prefix="+c", sep="/", size=2),
+            Alias(fancy, name="fancy", prefix="+f"),
+            Alias(label, name="label", prefix="+l"),
+            Alias(unit, name="unit", prefix="+u"),
+            Alias(vertical, name="vertical", prefix="+v"),
+        ],
+        p=Alias(perspective, name="perspective"),
+    ).add_common(
+        V=verbose,
+        t=transparency,
+    )
+
+    with Session() as lib:
+        lib.call_module(module="basemap", args=build_arg_list(aliasdict))