add option to show grid in skymap with projection

changelog.md

@@ -1,6 +1,7 @@
 ## [0.11.0] - WIP
 ### Changed
 - Using new Matplotlib `pcolormesh` API introduced in v3.7.0 to plot sky map with projections faster with less memory
+- Add option to plot grid in sky map with projection (e.g., "aitoff")
 
 ## [0.10.0] - 1 March 2023
 ### Changed

docs/source/matplotlib_single.rst

@@ -83,3 +83,28 @@ MilkyWay Sky Map
     mw1.scatter(lsmc_ra, lsmc_dec, c="r", s=200)
 
 .. image:: matplotlib_imgs/single_lmcsmc.jpg
+
+You can also plot with grid
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. code-block:: python
+    :linenos:
+
+    import numpy as np
+    from astropy import units as u
+    from mw_plot import MWSkyMap
+
+    # setup a MWSkyMap instance with projection, other projection can be 'hammer', 'mollweide' etc
+    # grid: whether to show the grid
+    mw1 = MWSkyMap(projection="aitoff", grid=True)
+
+    # set up plot title
+    mw1.title = "LMC and SMC in red dots"
+
+    # LMC and SMC coordinates
+    lsmc_ra = [78.77, 16.26] * u.degree
+    lsmc_dec = [-69.01, -72.42] * u.degree
+
+    mw1.scatter(lsmc_ra, lsmc_dec, c="r", s=200)
+
+.. image:: matplotlib_imgs/single_lmcsmc_w_grid.jpg

mw_plot/mw_plot_masters.py

@@ -262,7 +262,7 @@ class MWSkyMapMaster(MWPlotMaster):
     MWSkyMap master class
     """
 
-    def __init__(self, grayscale, projection, center, radius, figsize, dpi):
+    def __init__(self, grayscale, projection, center, radius, figsize, dpi, grid=False):
         if projection in [
             "equirectangular",
             "aitoff",
@@ -279,11 +279,16 @@ def __init__(self, grayscale, projection, center, radius, figsize, dpi):
         self._grayscale = grayscale
         self.figsize = figsize
         self.dpi = dpi
+        self.grid = grid
         self._gh_imgbase_url = (
             "https://github.com/henrysky/milkyway_plot/raw/master/mw_plot/"
         )
         self._initialized = False
 
+        self._opposite_color = "white"
+        if self._grayscale:
+            self._opposite_color = "black"
+
         # check if running in browser-based ipython (aka jupyter)
         self._in_jupyter = False
         try:

mw_plot/mw_plot_matplotlib.py

@@ -439,6 +439,8 @@ class MWSkyMap(MWSkyMapMaster):
     :type radius: astropy.Quantity
     :param grayscale: whether to use grayscale background
     :type grayscale: bool
+    :param grid: whether to show grid
+    :type grid: bool
 
     :param figsize: Matplotlib figure size
     :type figsize: turple
@@ -452,6 +454,7 @@ def __init__(
         center=(0, 0) * u.deg,
         radius=(180, 90) * u.deg,
         grayscale=False,
+        grid=False,
         figsize=(10, 6.5),
         dpi=None,
     ):
@@ -462,6 +465,7 @@ def __init__(
             radius=radius,
             figsize=figsize,
             dpi=dpi,
+            grid=grid,
         )
         self._unit = u.degree
         self.fontsize = 20
@@ -616,10 +620,15 @@ def initialize_mwplot(self, fig=None, ax=None):
                 length=self.fontsize / 2,
             )
             if self.title is not None:
-                ax.set_title(self.title, fontsize=self.fontsize)
+                ax.set_title(self.title, fontsize=self.fontsize, y=1.05)
             self.fig, self.ax = fig, ax
 
             self._initialized = True
+            if self.grid is True:
+                for i in [0, -15, 15, -30, 30, -45, 45, -60, 60, -75, 75]:
+                    self.ax.plot(np.deg2rad([-180, 180]), np.deg2rad([i, i]), c=self._opposite_color, lw=0.5, zorder=3)
+                for i in [-150, -120, -90, -60, -30, 0, 30, 60, 90, 120, 150]:
+                    self.ax.plot(np.deg2rad([i, i]), np.deg2rad([-75, 75]), c=self._opposite_color, lw=0.5, zorder=3)
 
     def show(self, *args, **kwargs):
         if self.fig is None: