Remote datasets: Add note for exact resolution (#3721)

* Add note for '12s' resolution of Mars relief dataset

* Add note for '56s' resolution of Mercury relief dataset

* Add note for '14s' resolution of Moon relief dataset

* Add note for '52s' resolution of Pluto relief dataset

Author: yvonnefroehlich

pygmt/datasets/mars_relief.py

@@ -67,7 +67,8 @@ def load_mars_relief(
     ----------
     resolution
         The grid resolution. The suffix ``d``, ``m`` and ``s`` stand for arc-degrees,
-        arc-minutes and arc-seconds.
+        arc-minutes and arc-seconds. Note that ``"12s"`` refers to a resolution of
+        12.1468873601 arc-seconds.
     region
         The subregion of the grid to load, in the form of a sequence [*xmin*, *xmax*,
         *ymin*, *ymax*] or an ISO country code. Required for grids with resolutions

pygmt/datasets/mercury_relief.py

@@ -65,7 +65,8 @@ def load_mercury_relief(
     ----------
     resolution
         The grid resolution. The suffix ``d``, ``m`` and ``s`` stand for arc-degrees,
-        arc-minutes and arc-seconds.
+        arc-minutes and arc-seconds. Note that ``"56s"`` refers to a resolution of
+        56.25 arc-seconds.
     region
         The subregion of the grid to load, in the form of a sequence [*xmin*, *xmax*,
         *ymin*, *ymax*] or an ISO country code. Required for grids with resolutions

pygmt/datasets/moon_relief.py

@@ -67,7 +67,8 @@ def load_moon_relief(
     ----------
     resolution
         The grid resolution. The suffix ``d``, ``m`` and ``s`` stand for arc-degrees,
-        arc-minutes and arc-seconds.
+        arc-minutes and arc-seconds. Note that ``"14s"`` refers to a resolution of
+        14.0625 arc-seconds.
     region
         The subregion of the grid to load, in the form of a sequence [*xmin*, *xmax*,
         *ymin*, *ymax*] or an ISO country code. Required for grids with resolutions

pygmt/datasets/pluto_relief.py

@@ -65,7 +65,8 @@ def load_pluto_relief(
     ----------
     resolution
         The grid resolution. The suffix ``d``, ``m`` and ``s`` stand for arc-degrees,
-        arc-minutes and arc-seconds.
+        arc-minutes and arc-seconds. Note that ``"52s"`` refers to a resolution of
+        52.0732883317 arc-seconds.
     region
         The subregion of the grid to load, in the form of a sequence [*xmin*, *xmax*,
         *ymin*, *ymax*] or an ISO country code. Required for grids with resolutions