Mapping trips from APRS archives

I recently created a map from APRS archives of a recent trip by some friends over about eight weeks through central and north west Australia and back by the southern coast.

Google Earth googleearth 01/11/2015 , 08:43:23

Above is a graphic of the created map, but the ‘real' map is not simply an image, but it is a kml file for Google Earth which you can view / zoom / scroll, for example in Google Maps by clicking on the map above.

This article explains how to create the kml file from APRS archives.

How to

Step1: fetch the archived posits from findu.com.

findu.com offers a valuable service that contains an archive of posits for about six months, a great service that is deserving of financial support.

To fetch the last 48 hours for YOURCALL, use http://www.findu.com/cgi-bin/posit.cgi?call=YOURCALL&start=48&comma=1&time=1.

The screen display looks like plain text, but it is HTML so use  your browser to save as plain text, for example:

  • in Firefox, choose File / Save page as  and choose Save as type text to save the file; or
  • select the entire page in the browser, Copy and Paste it into a plain ascii editor and save it as a text file.

Documentation of the findu posit report parameters is at posit – displays parsed position reports.

Step 2: Convert to kml using GPSBabel

GPSBabel is a great file converter, free, and again deserving of financial support.

Script findu.bat for Windows accepts two optional positional parameters, a file name (without extension, default is finduposit) and colour (in the form AABBGGRR in hex, default is ff0000bf for red).

@echo off

rem convert track findu (eg from http://www.findu.com/cgi-bin/posit.cgi?call=VK4ZZ&start=99&comma=1&time=1) to kml
rem copy the screen output and paste it into an ascii editor (for html to text conversion).

set findu=finduposit
if not *%1==* set findu=%1
set colour=ff0000bf
if not *%2==* set colour=%2

set GPSBABEL="\Program Files\gpsbabel\gpsbabel"

%GPSBABEL% -i xcsv,style=finduposit.sty -f %findu%.txt -x transform,rte=wpt,del -x simplify,error=0.01k -o kml,track=1,points=0,labels=0,line_color=%colour%,line_width=3 -F %findu%.kml

GPSBabel is available for *nix, and a shell script could be written for similar behaviour.

finduposit.bat uses a gpsbabel style file finduposit.sty to describe the format of the input data as follows.

# Author: Owen
#   Date: 27/10/2015
#

DESCRIPTION  custom
EXTENSION    tab

#
# FILE LAYOUT DEFINITIIONS:
#
FIELD_DELIMITER COMMA
RECORD_DELIMITER NEWLINE

#
# INDIVIDUAL DATA FIELDS, IN ORDER OF APPEARANCE:
IFIELD GMT_TIME,"","%Y%m%d%H%M%S" # Datetime
IFIELD LAT_DECIMAL,"","%f" # Latitude
IFIELD LON_DECIMAL,"","%f" # Longitude
IFIELD PATH_COURSE,"","%f" # Course
IFIELD PATH_SPEED_KNOTS,"","%f" # Speed
IFIELD ALT_FEET,"","%.0f" #Elevation

Supplementing APRS

APRS has a host of issues that degrade the quality of such mapping, and a solution is to collect a stand alone track log of your trip. A simple inexpensive extension to typical APRS configurations is described at OpenLog for TinyTrak. Comparisons of the stand alone track with APRS are given at OpenLog for TinyTrak – drive test.