I signed up for a
ZoomIn API Key (not that it seems to be needed atm…) the other week and finally got a chance to have a play this past weekend.
My test case was to build a map of all the
CRCnet sites and the links between them to use as a plugin in the
CRCnet Configuration System. Either as a dynamic status display (colouring links to show traffic loads and status etc) or as a network planning tool to get a feel for the relationship between existing sites and potential new locations. Obviously the lack of topographical information makes the second case far less useful than it could be, but I think even in 2D it would still be a useful tool.
Getting the points onto the map was relatively straightforward, but adding any sort of hover event to them was another matter. The GEvent class currently only supports the click event and markers are not added with any other identifying attributes (such as an ID or Name) which could be used to hook an event into them. After a quick squiz at the Terms and Conditions, I grabbed a copy of the API javascript and after unobfuscating it (basically just adding back in line breaks and running in through indent(1)) started to have a squiz at what was happening. The API code is very nice and clean and it wasn’t at all hard to work out what was going on. Mozilla’s Venkman javascript debugger absolutely rocks for this sort of work. It allows you to step through all the scripts on the page line by line and quickly get a feel for the flow of the code.
Adding support for the hover (onmouseover) event doesn’t look like it would be too hard, but the T&C didn’t explicitly mention whether I was allowed to actually modify the API code, so I choose to simply create a CRCnetMarker class (see below) that creates GMarker object and then pokes id attributes onto the internal objects of that class before returning it. Then once you’ve called addOverlay you can use the basic DOM functions to hook in an onmouseover event handler on the ID of the marker.
var CRCnetMarker = function (sitename, point, icon)
var marker = new GMarker(point, icon);
marker.icon.id = "crcnet_container_" + sitename;
marker.icon.firstChild.id = "crcnet_icon_" + sitename;
marker.addEventListener = function (eventname, handler)
b = document.getElementById(marker.icon.firstChild.id);
b.addEventListener(eventname, handler, false);
return marker;
var marker = new CRCnetMarker(new GPoint(2704685.21,6367057.51), "mph");
map.addOverlay(marker);
marker.addEventListener('mouseover', hoverHandler);
That worked like a charm and I now have nice little info boxes popping up next to each node when you hover over them. I also discovered in the process of implementing this that
Prototype and ZoomIn do not play nicely together. It appears to be Prototype’s fault as it messes with the Array type by adding new methods (like each for enumeration) which break the builtin for (i in array) syntax when the array contains non-numeric keys (like each). This has been reported in the
prototype bug tracker as breaking Yahoo Maps but the comments don’t seem to offer much hope for Prototype’s behaviour changing anytime soon which is a pity.
The next roadblock was a lack of support for drawing lines! This put the kibosh on the whole animated network status idea. Trolling through the source again reveals a GPolyLine class that appears to be semi-implemented, so hopefully support for drawing lines is coming very soon.
The only other thing I found slightly annoying was having to supply all the co-ordinates in NZGD49 format. Most of our GPS information for CRCnet is stored in WGS84 format (as that’s what our older GPS unit puts out). NZGD49 has been deprecated in favour of NZGD2000 (which is near enough to identical to WGS84 for normal use) so I’m not really sure why ZoomIn is still using NZGD49. Maybe that’s all TerraLink can supply?
Some quick googling turned up the
proj library (apt-get install proj in Debian) which provides the cs2cs utility which can convert from WGS84 (aka NZGD2000) to NZGD49 to feed to ZoomIn. The magic peice of information is the transformation parameters which
LINZ helpfully provide. Punching those (I chose the 7 parameter version) into cs2cs via a command line like
echo "$lat $long" /usr/bin/cs2cs +proj=latlong +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0 +nodefs +to +proj=nzmg +datum=nzgd49 +ellps=intl +towgs84=59.47,-5.04,187.44,-0.47,0.10,-1.024,-4.5993 awk ' print $1" "$2 '
performs the magic conversion.
The conclusion?
Overall I think ZoomIn rocks and it’s really cool to see a small NZ company filling in where Google and friends have failed miserably.
The biggest weakness at the moment is definitely the API, which doesn’t really allow you to do much more than add points at this stage. Given that ZoomIn is still relatively young the leanness off the API is understandable. Given the API a few more months to mature and fill out and I think we’ll be able to create some really cool applications on top of the ZoomIn platform.
Screenshot:
