Figure.legend: Add parameters position/width/height/line_spacing to specify legend position and properties (#4046)

Author: seisman

examples/gallery/basemaps/double_y_axes.py

@@ -20,6 +20,7 @@ class can control which axes should be plotted and optionally show annotations,
 # %%
 import numpy as np
 import pygmt
+from pygmt.params import Position
 
 # Generate two sample Y-data from one common X-data
 x = np.linspace(1.0, 9.0, num=9)
@@ -63,8 +64,7 @@ class can control which axes should be plotted and optionally show annotations,
 # Plot points for y2-data
 fig.plot(x=x, y=y2, style="s0.28c", fill="red", label="y2")
 
-# Create a legend in the Top Left (TL) corner of the plot with an
-# offset of 0.1 centimeters
-fig.legend(position="jTL+o0.1c", box=True)
+# Create a legend in the Top Left (TL) corner of the plot with a 0.1-cm offset.
+fig.legend(position=Position("TL", offset=0.1), box=True)
 
 fig.show()

examples/gallery/embellishments/legend.py

@@ -2,21 +2,21 @@
 Legend
 ======
 
-The :meth:`pygmt.Figure.legend` method can automatically create a legend for
-symbols plotted using :meth:`pygmt.Figure.plot`. A legend entry is only added
-when the ``label`` parameter is used to state the desired text. Optionally,
-to adjust the legend, users can append different modifiers. A list of all
-available modifiers can be found at :gmt-docs:`gmt.html#l-full`. To create a
-multiple-column legend **+N** is used with the desired number of columns.
-For more complicated legends, users may want to write an ASCII file with
-instructions for the layout of the legend items and pass it to the ``spec``
-parameter of :meth:`pygmt.Figure.legend`. For details on how to set up such a
+The :meth:`pygmt.Figure.legend` method can automatically create a legend for symbols
+plotted using :meth:`pygmt.Figure.plot`. A legend entry is only added when the ``label``
+parameter is used to state the desired text. Optionally, to adjust the legend, users can
+append different modifiers. A list of all available modifiers can be found at
+:gmt-docs:`gmt.html#l-full`. To create a multiple-column legend **+N** is used with the
+desired number of columns. For more complicated legends, users may want to write an
+ASCII file with instructions for the layout of the legend items and pass it to the
+``spec`` parameter of :meth:`pygmt.Figure.legend`. For details on how to set up such a
 file, please see the GMT documentation at :gmt-docs:`legend.html#legend-codes`.
 """
 
 # %%
 import numpy as np
 import pygmt
+from pygmt.params import Position
 
 # Set up some test data
 x = np.arange(-10, 10.2, 0.2)
@@ -39,13 +39,11 @@
 
 # Use the label parameter to state the text label for the legend entry
 fig.plot(x=x, y=y1, pen="1p,green3", label="sin(x)+1.1")
-
 fig.plot(x=x, y=y2, style="c0.07c", fill="dodgerblue", label="cos(x)+1.1")
 
-# Add a legend to the plot; place it within the plot bounding box with both
-# reference ("J") and anchor ("+j") points being the Top Right (TR) corner and an
-# offset of 0.2 centimeters in x- and y-directions; surround the legend with a box
-fig.legend(position="JTR+jTR+o0.2c", box=True)
+# Add a legend to the plot at the Top Right (TR) corner with a 0.2-cm offset in x- and
+# y-directions; surround the legend with a box.
+fig.legend(position=Position("TR", offset=0.2), box=True)
 
 # -----------------------------------------------------------------------------
 # Bottom: Horizontal legend (here two columns)
@@ -55,8 +53,8 @@
 
 fig.plot(x=x, y=y4, style="s0.07c", fill="orange", label="cos(x/2)-1.1")
 
-# For a multi-column legend, users have to provide the width via "+w", here it is
-# set to 6 centimeters; reference and anchor points are the Bottom Right (BR) corner
-fig.legend(position="JBR+jBR+o0.2c+w6c", box=True)
+# For a multi-column legend, users have to provide the width, here it is set to 6 cm;
+# the legend is placed at the Bottom Right (BR) corner.
+fig.legend(position=Position("BR", offset=0.2), width="6c", box=True)
 
 fig.show()

examples/gallery/lines/hlines_vlines.py

@@ -12,7 +12,7 @@
 # In Cartesian coordinate systems lines are plotted as straight lines.
 
 import pygmt
-from pygmt.params import Box
+from pygmt.params import Box, Position
 
 fig = pygmt.Figure()
 
@@ -32,7 +32,7 @@
 fig.hlines(
     y=[2, 3], xmin=[0, 1], xmax=[7, 7.5], pen="1.5p,dodgerblue3", label="Lines 7 & 8"
 )
-fig.legend(position="JBR+jBR+o0.2c", box=Box(pen="1p", fill="white"))
+fig.legend(position=Position("BR", offset=0.2), box=Box(pen="1p", fill="white"))
 
 fig.shift_origin(xshift="w+2c")
 

examples/tutorials/advanced/legends.py

@@ -10,7 +10,7 @@
 import io
 
 import pygmt
-from pygmt.params import Box
+from pygmt.params import Box, Position
 
 # %%
 # Create an auto-legend
@@ -47,9 +47,8 @@
 # Adjust the position
 # -------------------
 #
-# Use the ``position`` parameter to adjust the position of the legend. Add an offset via
-# **+o** for the x- and y-directions. Additionally append **+w** to adjust the width
-# of the legend. Note, no box is drawn by default if ``position`` is used.
+# Use the ``position`` parameter to adjust the position of the legend. Note, no box is
+# drawn by default if ``position`` is used.
 
 fig = pygmt.Figure()
 fig.basemap(region=[-5, 5, -5, 5], projection="X5c", frame=True)
@@ -58,20 +57,17 @@
 fig.plot(x=1, y=0, style="t0.3c", fill="pink", pen="black", label="pink triangle")
 fig.plot(x=[-3, 3], y=[-2, -2], pen="darkred", label="darkred line")
 
-# Set the reference point to the Top Left corner within (lowercase "j") the bounding box
-# of the plot and use offsets of 0.3 and 0.2 centimeters in the x- and y-directions,
-# respectively.
-fig.legend(position="jTL+o0.3c/0.2c")
+# Set the reference point to the Top Left corner inside the plot and use offsets of 0.3
+# and 0.2 centimeters in the x- and y-directions, respectively.
+fig.legend(position=Position("TL", offset=(0.3, 0.2)))
 
 fig.show()
 
 
 # %%
 # Add a box
 # ---------
-# Use the ``box`` parameter for adjusting the box around the legend. The outline of the
-# box can be adjusted by appending **+p**. Append **+g** to fill the legend with a color
-# (or pattern) [Default is no fill]. The default of ``position`` is preserved.
+# Use the ``box`` parameter for adjusting the box around the legend.
 
 fig = pygmt.Figure()
 fig.basemap(region=[-5, 5, -5, 5], projection="X5c", frame="rltb+glightgray")
@@ -80,7 +76,7 @@
 fig.plot(x=1, y=0, style="t0.3c", fill="pink", pen="black", label="pink triangle")
 fig.plot(x=[-3, 3], y=[-2, -2], pen="darkred", label="darkred line")
 
-fig.legend(position="jTL+o0.3c/0.2c", box=True)
+fig.legend(position=Position("TL", offset=(0.3, 0.2)), box=True)
 
 fig.shift_origin(xshift="w+1c")
 fig.basemap(region=[-5, 5, -5, 5], projection="X5c", frame="rltb+glightgray")
@@ -91,7 +87,9 @@
 
 # Add a box with a 2-point thick blue, solid outline and a white fill with a
 # transparency of 30 percent ("@30").
-fig.legend(position="jTL+o0.3c/0.2c", box=Box(pen="2p,blue", fill="white@30"))
+fig.legend(
+    position=Position("TL", offset=(0.3, 0.2)), box=Box(pen="2p,blue", fill="white@30")
+)
 
 fig.show()
 
@@ -146,15 +144,14 @@
 
 # %%
 # Now, we can add a legend based on this :class:`io.StringIO` object. For multi-columns
-# legends, the width (**+w**) has to be specified via a the ``position`` parameter.
-
+# legends, the width must be specified.
 fig = pygmt.Figure()
 # Note, that we are now using a Mercator projection
 fig.basemap(region=[-5, 5, -5, 5], projection="M10c", frame=True)
-
 # Pass the io.StringIO object to the "spec" parameter
-fig.legend(spec=spec_io, position="jMC+w9c", box=Box(pen="1p,gray50", fill="gray95"))
-
+fig.legend(
+    spec=spec_io, position="MC", width="9c", box=Box(pen="1p,gray50", fill="gray95")
+)
 fig.show()
 
 # sphinx_gallery_thumbnail_number = 4

examples/tutorials/basics/plot.py

@@ -13,6 +13,7 @@
 import io
 
 import pygmt
+from pygmt.params import Position
 
 # %%
 # For example, let's load the sample dataset of tsunami generating earthquakes
@@ -71,7 +72,7 @@
 legend = io.StringIO(
     "\n".join(f"S 0.4 c {0.02 * 2**m:.2f} - 1p 1 Mw {m}" for m in [3, 4, 5])
 )
-fig.legend(spec=legend, position="jBR+o0.2c+l2", box=True)
+fig.legend(spec=legend, position=Position("BR", offset=0.2), line_spacing=2.0, box=True)
 fig.show()
 
 # %%
@@ -101,7 +102,7 @@
     pen="black",
 )
 fig.colorbar(frame="xaf+lDepth (km)")
-fig.legend(spec=legend, position="jBR+o0.2c+l2", box=True)
+fig.legend(spec=legend, position=Position("BR", offset=0.2), line_spacing=2.0, box=True)
 fig.show()
 
 # sphinx_gallery_thumbnail_number = 3

pygmt/src/legend.py

@@ -6,50 +6,52 @@
 from collections.abc import Sequence
 from typing import Literal
 
-from pygmt._typing import PathLike
+from pygmt._typing import AnchorCode, PathLike
 from pygmt.alias import Alias, AliasSystem
 from pygmt.clib import Session
 from pygmt.exceptions import GMTTypeError
-from pygmt.helpers import (
-    build_arg_list,
-    data_kind,
-    fmt_docstring,
-    is_nonstr_iter,
-    use_alias,
-)
-from pygmt.params import Box
+from pygmt.helpers import build_arg_list, data_kind, fmt_docstring, is_nonstr_iter
+from pygmt.params import Box, Position
+from pygmt.src._common import _parse_position
 
 
 @fmt_docstring
-@use_alias(D="position")
 def legend(  # noqa: PLR0913
     self,
     spec: PathLike | io.StringIO | None = None,
-    scale: float | None = None,
-    position="JTR+jTR+o0.2c",
+    position: Position | Sequence[float | str] | AnchorCode | None = None,
+    width: float | str | None = None,
+    height: float | str | None = None,
+    line_spacing: float | None = None,
     box: Box | bool = False,
+    scale: float | None = None,
     projection: str | None = None,
     region: Sequence[float | str] | str | None = None,
     frame: str | Sequence[str] | bool = False,
     verbose: Literal["quiet", "error", "warning", "timing", "info", "compat", "debug"]
     | bool = False,
     panel: int | Sequence[int] | bool = False,
-    transparency: float | None = None,
     perspective: float | Sequence[float] | str | bool = False,
+    transparency: float | None = None,
     **kwargs,
 ):
-    r"""
+    """
     Plot a legend.
 
-    Makes legends that can be overlaid on maps. Reads specific
-    legend-related information from an input file, or automatically creates
-    legend entries from plotted symbols that have labels. Unless otherwise
-    noted, annotations will be made using the primary annotation font and
-    size in effect (i.e., :gmt-term:`FONT_ANNOT_PRIMARY`).
+    Makes legends that can be overlaid on plots. It reads specific legend-related
+    information from an input file, a :class:`io.StringIO` object, or automatically
+    creates legend entries from plotted symbols that have labels. Unless otherwise
+    noted, annotations will be made using the primary annotation font and size in effect
+    (i.e., :gmt-term:`FONT_ANNOT_PRIMARY`).
 
     Full GMT docs at :gmt-docs:`legend.html`.
 
-    $aliases
+    **Aliases:**
+
+    .. hlist::
+       :columns: 3
+
+       - D = position, **+w**: width/height, **+l**: line_spacing
        - B = frame
        - F = box
        - J = projection
@@ -71,13 +73,32 @@ def legend(  # noqa: PLR0913
         - A :class:`io.StringIO` object containing the legend specification
 
         See :gmt-docs:`legend.html` for the definition of the legend specification.
-    position : str
-        [**g**\|\ **j**\|\ **J**\|\ **n**\|\ **x**]\ *refpoint*\
-        **+w**\ *width*\ [/*height*]\ [**+j**\ *justify*]\ [**+l**\ *spacing*]\
-        [**+o**\ *dx*\ [/*dy*]].
-        Define the reference point on the map for the legend. By default, uses
-        **JTR**\ **+jTR**\ **+o**\ 0.2c which places the legend at the Top Right corner
-        inside the map frame, with a 0.2 cm offset.
+    position
+        Position of the legend 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 Top Right corner inside the plot with a 0.2-cm
+        offset.
+    width
+    height
+        Width and height of the legend box. If not given, the width and height are
+        computed automatically based on the contents of the legend specification. If
+        unit is ``%`` (percentage) then width is computed as that fraction of the plot
+        width. If height is given as percentage then height is recomputed as that
+        fraction of the legend width (not plot height).
+
+        **Note:** Currently, the automatic height calculation only works when legend
+        codes **D**, **H**, **L**, **S**, or **V** are used and that the number of
+        symbol columns (**N**) is 1.
+    line_spacing
+        The line-spacing factor between legend entries in units of the current font size
+        [Default is 1.1].
     box
         Draw a background box behind the legend. If set to ``True``, a simple
         rectangular box is drawn using :gmt-term:`MAP_FRAME_PEN`. To customize the box
@@ -95,11 +116,20 @@ def legend(  # noqa: PLR0913
     """
     self._activate_figure()
 
-    # Default position and box when not specified.
-    if kwargs.get("D") is None:
-        kwargs["D"] = position
-        if box is False and kwargs.get("F") is None:
-            box = Box(pen="1p", fill="white")  # Default box
+    # Set default box if both position and box are not given.
+    # The default position will be set later in _parse_position().
+    if kwargs.get("D", position) is None and kwargs.get("F", box) is False:
+        box = Box(pen="1p", fill="white")
+
+    position = _parse_position(
+        position,
+        kwdict={"width": width, "height": height, "line_spacing": line_spacing},
+        default=Position("TR", offset=0.2),  # Default to TR with 0.2-cm offset.
+    )
+
+    # Set width to 0 (auto calculated) if height is given but width is not.
+    if height is not None and width is None:
+        width = 0
 
     kind = data_kind(spec)
     if kind not in {"empty", "file", "stringio"}:
@@ -110,6 +140,12 @@ def legend(  # noqa: PLR0913
         )
 
     aliasdict = AliasSystem(
+        D=[
+            Alias(position, name="position"),
+            Alias(width, name="width", prefix="+w"),  # +wwidth/height
+            Alias(height, name="height", prefix="/"),
+            Alias(line_spacing, name="line_spacing", prefix="+l"),
+        ],
         F=Alias(box, name="box"),
         S=Alias(scale, name="scale"),
     ).add_common(

pygmt/tests/baseline/test_legend_position.png.dvc

@@ -0,0 +1,5 @@
+outs:
+- md5: 88cdea7af99c1edd19ade5b4c9b6c09e
+  size: 115141
+  hash: md5
+  path: test_legend_width_height.png