Is there a way to pass javascript variables in url?

Try this:

 window.location.href = "http://www.gorissen.info/Pierre/maps/googleMapLocation.php?lat="+elemA+"&lon="+elemB+"&setLatLon=Set";

To put a variable in a string enclose the variable in quotes and addition signs like this:

var myname = "BOB";
var mystring = "Hi there "+myname+"!"; 

Just remember that one rule!

Do you mean include javascript variable values in the query string of the URL?

Yes:

 window.location.href = "http://www.gorissen.info/Pierre/maps/googleMapLocation.php?lat="+var1+"&lon="+var2+"&setLatLon="+varEtc;

Summary

With either string concatenation or string interpolation (via template literals).

Here with JavaScript template literal:

function geoPreview() {
    var lat = document.getElementById("lat").value;
    var long = document.getElementById("long").value;

    window.location.href = `http://www.gorissen.info/Pierre/maps/googleMapLocation.php?lat=${lat}&lon=${long}&setLatLon=Set`;
}

Both parameters are unused and can be removed.

Remarks

String Concatenation

Join strings with the + operator:

window.location.href = "http://www.gorissen.info/Pierre/maps/googleMapLocation.php?lat=" + elemA + "&lon=" + elemB + "&setLatLon=Set";

String Interpolation

For more concise code, use JavaScript template literals to replace expressions with their string representations. Template literals are enclosed by `` and placeholders surrounded with ${}:

window.location.href = `http://www.gorissen.info/Pierre/maps/googleMapLocation.php?lat=${elemA}&lon=${elemB}&setLatLon=Set`;

Template literals are available since ECMAScript 2015 (ES6).