Implement showing GPS ranges in meter

sohstationviewer/model/mseed/mseed.py

@@ -351,7 +351,7 @@ class MSeed(DataTypeModel):
 
         # If location data is missing, we set them to 0.
         if gps_status_lines[5] == 'Latitude: ':
-            return GPSPoint(last_timemark, fix_type, 0, 0, 0, 0)
+            return GPSPoint(last_timemark, fix_type, 0, 0, 0, 0, '')
 
         num_sats_used = int(gps_status_lines[8].split(': ')[1])
 

sohstationviewer/view/plotting/gps_dialog.py

+import math
 import sys
 from pathlib import Path
 from typing import List
@@ -46,8 +47,22 @@ class GPSWidget(QtWidgets.QWidget):
         max_longitude = max(all_longitudes)
         min_longitude = min(all_longitudes)
 
+        latitude_range = max_latitude - min_latitude
+        longitude_range = max_longitude - min_longitude
+        longitude_range = convert_longitude_degree_to_meter(longitude_range,
+                                                            latitude_range)
+        latitude_range = convert_latitude_degree_to_meter(latitude_range)
+
         self.ax.plot(all_longitudes, all_latitudes, 'ws', markersize=4,
                      markeredgecolor='black', picker=True, pickradius=4)
+        range_text = (
+            f'Lat range: {latitude_range:.2f}m    '
+            f'Long range: {longitude_range:.2f}m'
+        )
+        self.ax.text(
+            0.01, 0.96, range_text, color='white', size=10,
+            transform=self.ax.transAxes
+        )
 
         latitude_range = max_latitude - min_latitude
         longitude_range = max_longitude - min_longitude
@@ -181,14 +196,41 @@ class GPSDialog(QtWidgets.QWidget):
                 outfile.write(line)
 
 
+# We use the WGS-84's version of the Earth ellipsoid as a reference point for
+# converting latitude and longitude differences from degree to meter.
+# The constants below are obtained from here
+# https://en.wikipedia.org/wiki/Earth_ellipsoid#Historical_Earth_ellipsoids.
+# In order to use other models of the Earth ellipsoid, simply change these
+# constants.
+POLAR_CIRCUMFERENCE = 40007863
+EQUATORIAL_CIRCUMFERENCE = 40075017
+
+
+def convert_latitude_degree_to_meter(lat: float) -> float:
+    # A whole circumference is 360 degrees, so we can get the length of one
+    # degree by dividing the circumference by 360.
+    lat_degree_length_in_meter = POLAR_CIRCUMFERENCE / 360
+    return lat * lat_degree_length_in_meter
+
+
+def convert_longitude_degree_to_meter(long: float, lat: float) -> float:
+    # A whole circumference is 360 degrees, so we can get the length of one
+    # degree by dividing the circumference by 360.
+    long_degree_length_in_meter = EQUATORIAL_CIRCUMFERENCE / 360
+    # The length of a longitude degree varies with the latitude, being greatest
+    # around the equator and approaching 0 near to the poles.
+    adjustment_for_latitude = math.cos(lat)
+    return long * long_degree_length_in_meter * adjustment_for_latitude
+
+
 if __name__ == '__main__':
     import os
 
     os.chdir('/Users/kle/PycharmProjects/sohstationviewer')
     app = QtWidgets.QApplication(sys.argv)
 
-    data_path = '/Users/kle/PycharmProjects/sohstationviewer/tests/test_data/Q330-sample'
-    # data_path = '/Users/kle/Documents/SOHView data/Q330/Q330_5281.sdr'
+    # data_path = '/Users/kle/PycharmProjects/sohstationviewer/tests/test_data/Q330-sample'
+    data_path = '/Users/kle/Documents/SOHView data/Q330/Q330_5281.sdr'
     data = MSeed(QtWidgets.QTextBrowser(), data_path)
 
     wnd = GPSDialog()
@@ -197,3 +239,6 @@ if __name__ == '__main__':
     wnd.show()
 
     sys.exit(app.exec_())
+
+
+