Add Figure.magnetic_rose to plot a magnetic rose on map

Author: seisman

doc/api/index.rst

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

pygmt/figure.py

@@ -422,6 +422,7 @@ def _repr_html_(self) -> str:
         inset,
         legend,
         logo,
+        magnetic_rose,
         meca,
         plot,
         plot3d,

pygmt/src/__init__.py

@@ -35,6 +35,7 @@
 from pygmt.src.inset import inset
 from pygmt.src.legend import legend
 from pygmt.src.logo import logo
+from pygmt.src.magnetic_rose import magnetic_rose
 from pygmt.src.makecpt import makecpt
 from pygmt.src.meca import meca
 from pygmt.src.nearneighbor import nearneighbor

pygmt/src/magnetic_rose.py

@@ -0,0 +1,147 @@
+"""
+magnetic_rose - Add a map magnetic rose.
+"""
+
+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 GMTInvalidInput
+from pygmt.helpers import build_arg_list, fmt_docstring
+from pygmt.params import Box, Position
+from pygmt.src._common import _parse_position
+
+
+@fmt_docstring
+def magnetic_rose(  # noqa: PLR0913
+    self,
+    position: Position | Sequence[float | str] | AnchorCode | None = None,
+    width: float | str | None = None,
+    labels: Sequence[str] | bool = False,
+    outer_pen: str | bool = False,
+    inner_pen: str | bool = False,
+    declination: float | None = None,
+    declination_label: str | None = None,
+    intervals: Sequence[float] | None = None,
+    box: Box | bool = False,
+    verbose: Literal["quiet", "error", "warning", "timing", "info", "compat", "debug"]
+    | bool = False,
+    panel: int | Sequence[int] | bool = False,
+    perspective: str | bool = False,
+    transparency: float | None = None,
+):
+    """
+    Add a magnetic rose to the map.
+
+    Parameters
+    ----------
+    position
+        Position of the magnetic rose on the plot. It can be specified in multiple ways:
+
+        - A :class:`pygmt.params.Position` object to fully control the reference point,
+          anchor point, and offset.
+        - A sequence of two values representing the x and y coordinates in plot
+          coordinates, e.g., ``(1, 2)`` or ``("1c", "2c")``.
+        - A :doc:`2-character justification code </techref/justification_codes>` for a
+          position inside the plot, e.g., ``"TL"`` for Top Left corner inside the plot.
+
+        If not specified, defaults to the bottom-left corner of the plot (position
+        ``(0, 0)`` with anchor ``"BL"``).
+    width
+        Width of the rose in plot coordinates, or append unit ``%`` for a size in
+        percentage of plot width [Default is 15%].
+    labels
+        A sequence of four strings to label the cardinal points W, E, S, N. Use an empty
+        string to skip a specific label. If the north label is ``"*"``, then a north
+        star is plotted instead of the north label. If set to ``True``, use the default
+        labels ``["W", "E", "S", "N"]``.
+    outer_pen
+        Draw the outer circle of the magnetic rose, using the given pen attributes.
+    inner_pen
+        Draw the inner circle of the magnetic rose, using the given pen attributes.
+    declination
+        Magnetic declination in degrees. By default, only a geographic north is plotted.
+        With this parameter set, a magnetic north is also plotted. A magnetic compass
+        needle is drawn inside the rose to indicate the direction to magnetic north.
+    declination_label
+        Label for the magnetic compass needle. Default is to format a label based on
+        ``declination``. To bypass the label, set to ``"-"``.
+    intervals
+        Specify the annotation and tick intervals for the geographic and magnetic
+        directions. It can be a sequence of three or six values. If three values are
+        given, they are used for both geographic and magnetic directions. If six values
+        are given, the first three are used for geographic directions and the last three
+        for magnetic directions. [Default is ``(30, 5, 1)``].
+        **Note**: If :gmt-term:`MAP_EMBELLISHMENT_MODE` is ``"auto"`` and the compass
+        size is smaller than 2.5 cm then the interval defaults are reset to
+        ``(90,30, 3, 45, 15, 3)``.
+    box
+        Draw a background box behind the magnetic 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 Position
+    >>> fig = pygmt.Figure()
+    >>> fig.basemap(region=[-10, 10, -10, 10], projection="M15c", frame=True)
+    >>> fig.magnetic_rose(
+    ...     position=Position((-5, -5), cstype="mapcoords"),
+    ...     width="4c",
+    ...     labels=["W", "E", "S", "*"],
+    ...     intervals=(45, 15, 3, 60, 20, 4),
+    ...     outer_pen="1p,red",
+    ...     inner_pen="1p,blue",
+    ...     declination=11.5,
+    ...     declination_label="11.5°E",
+    ... )
+    >>> fig.show()
+    """
+    self._activate_figure()
+
+    position = _parse_position(
+        position,
+        kwdict={
+            "width": width,
+            "labels": labels,
+            "outer_pen": outer_pen,
+            "inner_pen": inner_pen,
+            "declination": declination,
+            "declination_label": declination_label,
+            "intervals": intervals,
+        },
+        default=Position("BL", cstype="inside"),  # Default to BL.
+    )
+
+    if declination_label is not None and declination is None:
+        msg = "Parameter 'declination' must be set when 'declination_label' is set."
+        raise GMTInvalidInput(msg)
+
+    aliasdict = AliasSystem(
+        F=Alias(box, name="box"),
+        Tm=[
+            Alias(position, name="position"),
+            Alias(width, name="width", prefix="+w"),
+            Alias(labels, name="labels", prefix="+l", sep=",", size=4),
+            Alias(outer_pen, name="outer_pen", prefix="+p"),
+            Alias(inner_pen, name="inner_pen", prefix="+i"),
+            Alias(declination, name="declination", prefix="+d"),
+            Alias(declination_label, name="declination_label", prefix="/"),
+            Alias(intervals, name="intervals", prefix="+t", sep="/", size=(3, 6)),
+        ],
+    ).add_common(
+        V=verbose,
+        c=panel,
+        p=perspective,
+        t=transparency,
+    )
+
+    with Session() as lib:
+        lib.call_module(module="basemap", args=build_arg_list(aliasdict))

pygmt/tests/baseline/test_magnetic_rose.png.dvc

@@ -0,0 +1,5 @@
+outs:
+- md5: 5af8ffee19917b1fbc3371cd3aed53cd
+  size: 27013
+  hash: md5
+  path: test_magnetic_rose.png

pygmt/tests/baseline/test_magnetic_rose_complete.png.dvc

@@ -0,0 +1,5 @@
+outs:
+- md5: 78c53322b2514fbcd56483b793d47ebe
+  size: 28831
+  hash: md5
+  path: test_magnetic_rose_complete.png

pygmt/tests/test_magnetic_rose.py

@@ -0,0 +1,50 @@
+"""
+Test Figure.magnetic_rose.
+"""
+
+import pytest
+from pygmt import Figure
+from pygmt.exceptions import GMTInvalidInput
+from pygmt.params import Position
+
+
+@pytest.mark.mpl_image_compare
+def test_magnetic_rose():
+    """
+    Create a map with a compass. Modified from the test_basemap_compass test.
+    """
+    fig = Figure()
+    fig.basemap(region=[127.5, 128.5, 26, 27], projection="M10c", frame=True)
+    fig.magnetic_rose()
+    return fig
+
+
+@pytest.mark.mpl_image_compare
+def test_magnetic_rose_complete():
+    """
+    Test all parameters of Figure.magnetic_rose.
+    """
+    fig = Figure()
+    fig.basemap(region=[-10, 10, -10, 10], projection="M10c", frame=True)
+    fig.magnetic_rose(
+        position=Position("BL"),
+        width="2c",
+        labels=["W", "E", "S", "*"],
+        intervals=(45, 15, 3, 60, 20, 4),
+        outer_pen="1p,red",
+        inner_pen="1p,blue",
+        declination=11.5,
+        declination_label="11.5°E",
+    )
+    return fig
+
+
+def test_magnetic_rose_invalid_declination_label():
+    """
+    Test that an exception is raised when declination_label is set but declination is
+    not set.
+    """
+    fig = Figure()
+    fig.basemap(region=[-10, 10, -10, 10], projection="M10c", frame=True)
+    with pytest.raises(GMTInvalidInput):
+        fig.magnetic_rose(declination_label="11.5°E")