diff options
| -rw-r--r-- | gps/misc.py | 18 | ||||
| -rwxr-xr-x | gpsprof | 16 |
2 files changed, 18 insertions, 16 deletions
diff --git a/gps/misc.py b/gps/misc.py index 0b343d6a..c5fac25e 100644 --- a/gps/misc.py +++ b/gps/misc.py @@ -146,6 +146,24 @@ def EarthDistance(c1, c2): a = -1 return CalcRad((lat1 +lat2) / 2) * math.acos(a) +def EarthDistanceSmall(c1, c2): + "Distance in meters between two close points specified in degrees." + # This calculation is known as an Equirectangular Projection + # fewer numeric issues for small angles that other methods + (lat1, lon1) = c1 + (lat2, lon2) = c2 + avglat = (lat1 + lat2 ) /2 + phi = math.radians( avglat ) # radians of avg latitude + # meters per degree at this latitude, corrected for WGS84 ellipsoid + # Note the wikipedia numbers are NOT ellipsoid corrected: + # https://en.wikipedia.org/wiki/Decimal_degrees#Precision + m_per_d = (111132.954 - 559.822 * math.cos(2 * phi) + + 1.175 * math.cos(4 * phi)) + dlat = (lat1 - lat2) * m_per_d + dlon = (lon1 - lon2) * m_per_d * math.cos( phi ) + + dist = math.sqrt( math.pow(dlat, 2) + math.pow(dlon, 2 )) + return dist; def MeterOffset(c1, c2): "Return offset in meters of second arg from first." @@ -20,22 +20,6 @@ import socket import sys import time -def EarthDistanceSmall(c1, c2): - "Distance in meters between two close points specified in degrees." - # This calculation is known as an Equirectangular Projection - # fewer numeric issues for small angles that other methods - (lat1, lon1) = c1 - (lat2, lon2) = c2 - dlat = lat1 - lat2 - avglat = (lat1 + lat2 ) /2 - dlon = (lon1 - lon2) * math.cos( math.radians( avglat ) ) - # Earth Mean Radius 6371000 meters. - # one degree lat, average 111.133000 - # at equator 110.567 km - # at poll 111.699 km - dist = math.sqrt( dlat * dlat + dlon * dlon) * 111133 - return dist; - class Baton(object): "Ship progress indication to stderr." |