Data Function to Compute Distance (in km & mi) between two points that have lat/long

Table of Contents

• Background
• Use Case
• Data Function Code

Background

Spotfire can automatically show the distance between points on a map (as shown in the image below).  Changing the selector type to a radius displays the distance from the center of the circle to the diameter.  Use the Properties menu to configure whether the display shows Miles or Kilometers.

Use Case

You might require a more accurate computation than a manual visual measure, and you want to bring the result into a Spotfire data table.  You can obtain such a measure by using a TERR data function. 

The attached file (distancebtwn2pts.7z) contains a data function file (distance.sfd) and a dxp file (distance.dxp) that uses the data function to compute the distance between two marked points.  Two columns (X and Y = Long and Lat) are passed into the data function and only the first 2 points are used in the distance calculation.  Both the Kilometers and Miles are computed and returned in a table.

Inputs:  Longitude_Column, Latitude_Column

Output:  Table (containing a Kilometers distance & Miles distance)

Data Function Code

# Inputs: 
#   longitude : column with logitude values 
#   latitude : column with latitude values  
# Outputs: 
#   myout : table with distance results (in Miles and Kilometers)

long1 = longitude[1]   
long2 = longitude[2]   
lat1 = latitude[1]   
lat2 = latitude[2]      
# Calculate distance in kilometers between two points   
earth.dist <- function (long1, lat1, long2, lat2)
   {
     rad <- pi/180
     a1 <- lat1 * rad
     a2 <- long1 * rad
     b1 <- lat2 * rad
     b2 <- long2 * rad
     dlon <- b2 - a2
     dlat <- b1 - a1
     a <- (sin(dlat/2))^2 + cos(a1) * cos(b1) * (sin(dlon/2))^2
     c <- 2 * atan2(sqrt(a), sqrt(1 - a))
     R <- 6378.145
     d <- R * c     
     return(d)
   }      
 dist_km <- earth.dist(long1,lat1,long2,lat2)   
 dist_mi <- dist_km / 1.609344      
 myout <- data.frame("dist_km"=dist_km,"dist_mi"=dist_mi)

Attachments

Download From Resources.

distancebtw2pts.7z