Javascript regex to validate GPS coordinates
===

I have a form where a user inserts the GPS coordinates of a location to a corresponding photo.  Its easy enough to filter out invalid numbers, since I just have to test for a range of (-90, 90), (-180, 180) for lat/long coordinates.

However, this also means that regular text is valid input.

I've tried changing the test pattern to

    var pattern= "^[a-zA-Z]" 

and is used in the function to detect alphabetical characters
    
    $(".lat").keyup(function(){
      var thisID= this.id;
      var num = thisID.substring(3, thisID.length);
      var thisVal = $(this).val();
      
      //if invalid input, show error message and hide save button
      if (pattern.test(thisVal)){
        $("#latError"+num).fadeIn(250);
        $("#save"+num).fadeOut(100)
      } 
      else { //otherwise, hide error message and show save
        $("#save"+num).fadeIn(250);
        $("#latError"+num).fadeOut(100);
      }
    });

However, this doesn't work as all input is valid.  What would solve this issue?