Here is an way of doing it with a combination of Data::Table and Math::Round. As others have mentioned, there may be a better algorithm for determining a match for lat/lon coordinates based on distances. However, the method below can be adjusted using the $tol variable. Using the two data tables that you provided and $tol = 10 I get one match in the joined table, using $tol = 50 all three match. 
#!/usr/bin/env perl

use strict;
use warnings;

use Data::Table;
use Math::Round;

my $tol = 50; # Tolerance, i.e. round values to the neared multiple of
+ $tol

my $t1 = Data::Table::fromCSV("data1.txt", 1, undef);

# Delete lat & lon columns are replace with rounded values
my $gps_lat_col = $t1->delCol("GPSlat");
my $gps_lon_col = $t1->delCol("GPSlon");
my @nGPSlat = map{ nearest($tol, $_) } @{$gps_lat_col};
my @nGPSlon = map{ nearest($tol, $_) } @{$gps_lon_col};
$t1->addCol(\@nGPSlat, "GPSlat");
$t1->addCol(\@nGPSlon, "GPSlon");
print "\nTable 1\n";
print $t1->csv;

my $t2 = Data::Table::fromCSV("data2.txt", 1, undef); #, { delimiter =
+> " " });

# Delete lat & lon columns are replace with rounded values
my $lat_col = $t2->delCol("Lat");             # Delete column 'age'.
my $lon_col = $t2->delCol("Lon");             # Delete column 'age'.
my @nlat = map{ nearest($tol, $_) } @{$lat_col};
my @nlon = map{ nearest($tol, $_) } @{$lon_col};
$t2->addCol(\@nlat, "Lat");
$t2->addCol(\@nlon, "Lon");
print "\nTable 2\n";
print $t2->csv;

# Join the tables for cases where the rounded lat/lon pairs are exact 
+matches
my $t3 = $t1->join($t2, Data::Table::INNER_JOIN, [ 'GPSlat', 'GPSlon' 
+], ['Lat', 'Lon']);

print "\nJoined Table\n";
print $t3->csv;

exit;

[download]
Output: 
Table 1
Seq#,TransType,LocnNum,TankNum,Date,TimeStart,TimeEnd,TktVol,AltVol,To
+talSrt,TotalEnd,Driver,Trip,Route,MeanDegC,MaxDegC,ColCd,Ccode,TestTy
+pe,TrpSdate,GPSlat,GPSlon
174,0,291061000,59,141130,104945,105755,3355,0,255094551,255094551,500
+5,2,505,3.0,3.5,00,00,00,141130,5140600,645550
175,0,250401500,133,141130,110343,110858,760,0,255102140,255102140,500
+5,2,505,3.0,3.2,00,00,00,141130,5141450,647450
176,0,250400800,29,141130,115529,120130,1695,0,255119079,255119079,500
+5,2,505,3.7,4.2,00,00,00,141130,5147650,656150

Table 2
LocnID,TestCo#,LastVol,LocnName,LocnAdr,Lat,Lon
291061000,205,3568,Evans Marcross,,5140600,645550
250401500,205,857,Thomas And Ptns Somerset,,5141450,647450
250400800,205,1727,Thomas J  Newton House,,5147650,656150

Joined Table
Seq#,TransType,LocnNum,TankNum,Date,TimeStart,TimeEnd,TktVol,AltVol,To
+talSrt,TotalEnd,Driver,Trip,Route,MeanDegC,MaxDegC,ColCd,Ccode,TestTy
+pe,TrpSdate,GPSlat,GPSlon,LocnID,TestCo#,LastVol,LocnName,LocnAdr
176,0,250400800,29,141130,115529,120130,1695,0,255119079,255119079,500
+5,2,505,3.7,4.2,00,00,00,141130,5147650,656150,250400800,205,1727,Tho
+mas J  Newton House,
175,0,250401500,133,141130,110343,110858,760,0,255102140,255102140,500
+5,2,505,3.0,3.2,00,00,00,141130,5141450,647450,250401500,205,857,Thom
+as And Ptns Somerset,
174,0,291061000,59,141130,104945,105755,3355,0,255094551,255094551,500
+5,2,505,3.0,3.5,00,00,00,141130,5140600,645550,291061000,205,3568,Eva
+ns Marcross,

[download]

In reply to Re: CSV Cross Referencing by kevbot
in thread CSV Cross Referencing by Jalcock501

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.