rdistaz: Distance and Azimuth from two points

In RSEIS: Seismic Time Series Analysis Tools

Distance and Azimuth from two points

Description

Calculate distance, Azimuth and Back-Azimuth from two points on Globe.

Usage

rdistaz(olat, olon, tlat, tlon)

Arguments

olat	origin latitude, degrees
olon	origin longitude, degrees
tlat	target latitude, degrees
tlon	target longitude, degrees

Details

The azimuth is returned in degrees from North.

Program is set up for one origin (olat, olon) pair and many target (tlat, tlon) pairs given as vectors.

If multiple olat and olon are given, the program returns a list of outputs for each.

If olat or any tlat is greater than 90 or less than -90, NA is returned and error flag is 0.

If any tlat and tlon is equal to olat and olon, the points are coincident. In that case the distances are set to zero, but the az and baz are NA, and the error flag is set to 0.

Value

List:

del	Delta, angle in degrees
az	Azimuth, angle in degrees
baz	Back Azimuth, angle in degrees from target to origin
dist	Distance in km
err	0 or 1, error flag. 0=error, 1=no error, see details

Author(s)

Jonathan M. Lees<[e-mail]>

See Also

along.great, getgreatarc

Examples

####  one point
d <- rdistaz(12, 23, -32,    -65)
d

####  many random target points
org <- c(80.222, -100.940)
targ <- cbind(runif(10, 10, 50), runif(10, 20, 100))


rdistaz(org[1], org[2], targ[,1], targ[,2])

############  if origin and target are identical
#####  the distance is zero, but the az and baz are not defined
rdistaz(80.222, -100.940, 80.222, -100.940)


########################   set one of the targets equal to the origin
targ[7,1] <- org[1]
targ[7,2] <- org[2]

rdistaz(org[1], org[2], targ[,1], targ[,2])

####  put in erroneous latitude data

targ[3,1] <-  -91.3


rdistaz(org[1], org[2], targ[,1], targ[,2])
###########
### New York and Chapel Hill
NY =list(lat=40.6698,  lon=286.0562)
CH = list(lat=35.92761, lon=280.9594)
##    h = GEOmap::distaz(CH$lat, CH$lon, NY$lat, NY$lon)
h = rdistaz(CH$lat, CH$lon, NY$lat, NY$lon)

####### get great circle ray path
RAY =  GEOmap::getgreatarc(CH$lat, CH$lon, NY$lat, NY$lon, 100)
#### get great circle through north pole
Nor1 =  GEOmap::getgreatarc(CH$lat, CH$lon, 90,  CH$lon,   100)
PROJ = GEOmap::setPROJ(2, CH$lat, CH$lon)
RAY.XY = GEOmap::GLOB.XY(RAY$lat, RAY$lon, PROJ)
Nor1.XY = GEOmap::GLOB.XY(Nor1$lat, Nor1$lon, PROJ)
 VEE1 = c(Nor1.XY$x[2]-Nor1.XY$x[1], Nor1.XY$y[2]-Nor1.XY$y[1])
     VEE2 = c(RAY.XY$x[2]-RAY.XY$x[1], RAY.XY$y[2]-RAY.XY$y[1] )
     VEE1 = VEE1/sqrt(sum(VEE1^2) )
VEE2 =  VEE2/sqrt(sum(VEE2^2) )
######  get angle from north:
 ANG =    acos( sum(VEE1*VEE2)     ) *180/pi
####   compare with h

print(paste(h$az, ANG, h$az-ANG) )

RSEIS documentation built on Sept. 13, 2024, 1:09 a.m.