I was just looking at this example:
http://gmaps-samples.googlecode.com/svn/trunk/googlebar/googlebar_directions.html
It has an interesting approach to retrieving directions for a central
point and an array of markers. You can look at the source, but briefly
it does this:
function getDirections(markers, tbody, num)
{
...
var dir = new GDirections();
GEvent.addListener(dir, "load", function() {
...
if ((num+1) < markers.length) getDirections(markers, tbody, (num
+1));
});
dir.load("from: ....);
}
It is called initially with the markers array and i=0 for the first
point. It creates a new GDirections for marker 'i' and when the load
event calls the function to calculate the distance, that function also
calls getDirections() again with i+1 for the next marker to be
processed. The key point is that it enforces serial processing of each
marker in the array, because the load event processes marker "i" and
then initiates processing of marker "i+1". On the other hand, it
creates a GDirection for every marker to be processed.
I think I can use this to process a series of GDirection queries in
sequence. Just put them in an array and when the 'load' listener
finishes with query "i", it initiates the query for "i+1".
I have some questions:
1. if there are N markers to be processed, this will create a
GDirections object for each one. Isn't that a lot of overhead? What if
there's 50 markers? How many GDirections is too many? Does it depend
on how big the result of the 'load' is (e.g. the result is inside the
GDirection object).
2. Generally, recursive solutions are usually easy/efficient to code,
but they use more resources. If there are N markers, this will end up
as N nested calls on the stack. Maybe not a problem for 5 points, but
what about 50 points? How deep is too deep?
3. In the code, each GDirection has a listener function for the 'load'
event. In this case, it's an anonymous function. Does it use fewer
resources to use a named function instead? If the function is
anonymous, does the GDirection object get a copy of the function, but
only a pointer if a named function is used?
4. I usually code my listener functions with "this", e.g.:
function onload()
{
var p=this.getPolyline();
mymap.addOverlay(p);
}
Does use of "this" depend on whether an anonymous or named function is
used? Same thing?
Thanks.
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