Introduce grdview aliases cmap for C and surftype for Q

Giving our grdview wrapper the ability to color plots! The cmap (C) parameter (which stands for colormap) should be straightforward, while the surftype (Q) parameter is a little bit more complicated. Some more tests added to check that we can indeed produce colored perspective-view plots.

Author: weiji14

pygmt/base_plotting.py

@@ -233,12 +233,26 @@ def grdimage(self, grid, **kwargs):
                 lib.call_module("grdimage", arg_str)
 
     @fmt_docstring
-    @use_alias(R="region", J="projection", Jz="zscale", JZ="zsize", p="perspective")
+    @use_alias(
+        R="region",
+        J="projection",
+        Jz="zscale",
+        JZ="zsize",
+        C="cmap",
+        Q="surftype",
+        p="perspective",
+    )
     @kwargs_to_strings(R="sequence", p="sequence")
     def grdview(self, reliefgrid, **kwargs):
         """
         Create 3-D perspective image or surface mesh from a grid.
 
+        Reads a 2-D grid file and produces a 3-D perspective plot by drawing a mesh,
+        painting a colored/gray-shaded surface made up of polygons, or by scanline
+        conversion of these polygons to a raster image. Options include draping a data
+        set on top of a surface, plotting of contours on top of the surface, and apply
+        artificial illumination based on intensities provided in a separate grid file.
+
         Full option list at :gmt-docs:`grdview.html`
 
         Parameters
@@ -249,6 +263,19 @@ def grdview(self, reliefgrid, **kwargs):
         zscale (Jz) or zsize (JZ) : float or str
             Set z-axis scaling or z-axis size.
 
+        cmap (C) : str
+            The name of the color palette table to use.
+
+        surftype (Q) : str
+            Specifies cover type of the reliefgrid. Select one of following settings:
+            1. 'm' for mesh plot [Default].
+            2. 'mx' or 'my' for waterfall plots (row or column profiles).
+            3. 's' for surface plot.
+            4. 'i' for image plot.
+            5. 'c'. Same as 'i' but will make nodes with z = NaN transparent.
+            For any of these choices, you may force a monochrome image by appending the
+            modifier +m.
+
         perspective (p) : list or str
             ``'[x|y|z]azim[/elev[/zlevel]][+wlon0/lat0[/z0]][+vx0/y0]'``.
             Select perspective view.

pygmt/tests/baseline/test_grdview_with_cmap_for_image_plot.png

@@ -83,3 +83,42 @@ def test_grdview_with_perspective_and_zsize(grid):
     fig = Figure()
     fig.grdview(reliefgrid=grid, perspective=[225, 30], zsize="10c")
     return fig
+
+
+@pytest.mark.mpl_image_compare
+def test_grdview_with_cmap_for_image_plot(grid):
+    """
+    Run grdview by passing in a reliefgrid and setting a colormap for producing an image
+    plot.
+    """
+    fig = Figure()
+    fig.grdview(reliefgrid=grid, cmap="oleron", surftype="i")
+    return fig
+
+
+@pytest.mark.mpl_image_compare
+def test_grdview_with_cmap_for_surface_monochrome_plot(grid):
+    """
+    Run grdview by passing in a reliefgrid and setting a colormap for producing a
+    surface monochrome plot.
+    """
+    fig = Figure()
+    fig.grdview(reliefgrid=grid, cmap="oleron", surftype="s+m")
+    return fig
+
+
+@pytest.mark.mpl_image_compare
+def test_grdview_with_cmap_for_perspective_surface_plot(grid):
+    """
+    Run grdview by passing in a reliefgrid and setting a colormap for producing a
+    surface plot with a 3D perspective viewpoint.
+    """
+    fig = Figure()
+    fig.grdview(
+        reliefgrid=grid,
+        cmap="oleron",
+        surftype="s",
+        perspective=[225, 30],
+        zscale=0.005,
+    )
+    return fig