simple command costmap api - first few functions (#3159)

* initial commit costmap_2d template

Signed-off-by: Stevedan Omodolor <stevedan.o.omodolor@gmail.com>

* finish task A and tested

* lint

* Update nav2_simple_commander/nav2_simple_commander/costmap_2d.py

Co-authored-by: Steve Macenski <stevenmacenski@gmail.com>

* fix trailing underscores

Signed-off-by: Stevedan Omodolor <stevedan.o.omodolor@gmail.com>
Co-authored-by: Steve Macenski <stevenmacenski@gmail.com>

nav2_simple_commander/nav2_simple_commander/costmap_2d.py

@@ -0,0 +1,73 @@
+#! /usr/bin/env python3
+# Copyright 2021 Samsung Research America
+# Copyright 2022 Stevedan Ogochukwu Omodolor
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import numpy as np
+
+
+class PyCostmap2D:
+    """
+    PyCostmap2D.
+
+    Costmap Python3 API for OccupancyGrids to populate from published messages
+    """
+
+    def __init__(self, occupancy_map):
+        self.size_x = occupancy_map.info.width
+        self.size_y = occupancy_map.info.height
+        self.resolution = occupancy_map.info.resolution
+        self.origin_x = occupancy_map.info.origin.position.x
+        self.origin_y = occupancy_map.info.origin.position.y
+        self.global_frame_id = occupancy_map.header.frame_id
+        self.costmap_timestamp = occupancy_map.header.stamp
+        # Extract costmap
+        self.costmap = np.array(occupancy_map.data, dtype=np.int8).reshape(
+            self.size_y, self.size_x)
+
+    def getSizeInCellsX(self):
+        """Get map width in cells."""
+        return self.size_x
+
+    def getSizeInCellsY(self):
+        """Get map height in cells."""
+        return self.size_y
+
+    def getSizeInMetersX(self):
+        """Get x axis map size in meters."""
+        return (self.size_x - 1 + 0.5) * self.resolution_
+
+    def getSizeInMetersY(self):
+        """Get y axis map size in meters."""
+        return (self.size_y - 1 + 0.5) * self.resolution_
+
+    def getOriginX(self):
+        """Get the origin x axis of the map [m]."""
+        return self.origin_x
+
+    def getOriginY(self):
+        """Get the origin y axis of the map [m]."""
+        return self.origin_y
+
+    def getResolution(self):
+        """Get map resolution [m/cell]."""
+        return self.resolution
+
+    def getGlobalFrameID(self):
+        """Get global frame_id."""
+        return self.global_frame_id
+
+    def getCostmapTimestamp(self):
+        """Get costmap timestamp."""
+        return self.costmap_timestamp