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 +1,124 @@
+"""
+magnetic_rose - Add a map magnetic rose.
+"""
+
+from collections.abc import Sequence
+from typing import Literal
+
+from pygmt.alias import Alias, AliasSystem
+from pygmt.clib import Session
+from pygmt.exceptions import GMTInvalidInput
+from pygmt.helpers import build_arg_list
+from pygmt.params import Box, Position
+
+
+def magnetic_rose(  # noqa: PLR0913
+    self,
+    position: Position | 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,
+    perspective: str | bool = False,
+    verbose: Literal["quiet", "error", "warning", "timing", "info", "compat", "debug"]
+    | bool = False,
+    transparency: float | None = None,
+):
+    """
+    Add a magnetic rose to the map.
+
+    The magnetic rose 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
+        Specify the location of the magnetic rose on a map. See
+        :class:`pygmt.params.Position` for details.
+    width
+        Width of the rose in plot coordinates (append **i** (inch), **cm**
+        (centimeters), or **p** (points)), or append % for a size in percentage of map
+        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 seqeunce 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()
+
+    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,
+        p=perspective,
+        t=transparency,
+    )
+
+    with Session() as lib:
+        lib.call_module(module="basemap", args=build_arg_list(aliasdict))

pygmt/tests/test_config.py

@@ -47,8 +47,21 @@ def test_config_font_one():
     """
     fig = Figure()
     with config(FONT="8p,red"):
-        fig.basemap(region=[0, 9, 0, 9], projection="C3/3/9c", compass="jTL+w3c+d4.5+l")
-    fig.basemap(compass="jBR+w3.5c+d-4.5+l")
+        fig.basemap(region=[0, 9, 0, 9], projection="C3/3/9c", frame="+n")
+        fig.magnetic_rose(
+            position_type="inside",
+            position="TL",
+            width="3c",
+            declination=4.5,
+            labels=True,
+        )
+    fig.magnetic_rose(
+        position_type="inside",
+        position="BR",
+        width="3.5c",
+        declination=-4.5,
+        labels=True,
+    )
     return fig
 
 
@@ -60,8 +73,21 @@ def test_config_font_annot():
     """
     fig = Figure()
     with config(FONT_ANNOT="6p,red"):
-        fig.basemap(region=[0, 9, 0, 9], projection="C3/3/9c", compass="jTL+w3c+d4.5")
-    fig.basemap(compass="jBR+w3.5c+d-4.5")
+        fig.basemap(region=[0, 9, 0, 9], projection="C3/3/9c", frame="+n")
+        fig.magnetic_rose(
+            position_type="inside",
+            position="TL",
+            width="3c",
+            declination=4.5,
+            labels=True,
+        )
+    fig.magnetic_rose(
+        position_type="inside",
+        position="BR",
+        width="3.5c",
+        declination=-4.5,
+        labels=True,
+    )
     return fig
 
 

pygmt/tests/test_magnetic_rose.py

@@ -0,0 +1,19 @@
+"""
+Test Figure.magnetic_rose.
+"""
+
+import pytest
+from pygmt import Figure
+
+
+@pytest.mark.mpl_image_compare(filename="test_basemap_compass.png")
+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="H15c", frame=True)
+    fig.magnetic_rose(
+        position_type="inside", position="MC", width="5c", declination=11.5
+    )
+    return fig