Hi If someone can help me with this would be great. I did a zoom pan with d3.js which is working fine:
function zoom() {
var e = d3.event
var scale = d3.event.scale;
canvas.save();
canvas.clearRect(0, 0, width, height);
canvas.beginPath();
canvas.translate(e.translate[0], e.translate[1]);
canvas.scale(scale, scale);
draw();
canvas.restore();
}
then I wanted to have the image only inside the canvas area and I did it like this:
function zoom() {
var scale = d3.event.scale;
var e = d3.event,
tx = Math.min(0, Math.max(e.translate[0], width - imgBG.width * e.scale)),
ty = Math.min(0, Math.max(e.translate[1], height - imgBG.height * e.scale))
canvas.save();
canvas.clearRect(0, 0, width, height);
canvas.beginPath();
canvas.translate(tx, ty);
canvas.scale(scale, scale);
draw();
canvas.restore();
}
Here is a the working code: https://jsfiddle.net/ux7gbedj/
The problem is that: for example when the fiddle is loaded and I start dragging from left to right, let say 2 times, the Image is not moving which is fine, but then when I try to drag from right to left I have to drag at least 3 times to start moving again, so I think I am not doing something very correct.
You need to feed the restricted translate coordinates (tx, ty) back into the zoom behaviour object, otherwise the d3.event translate coordinates are unbounded and eventually you'll find the image sticks at one of the corners/sides. i.e. you'll be trying to restrict the image dragging to a window of say -200<x<0 with your min/max's but your translate.x coordinate could be at -600 after some continuous dragging. Even if you then drag back 50 pixels to -550, the image will not move, as it will max() to -200 in your code.
Logic taken from http://bl.ocks.org/mbostock/4987520
...
// declare the zoom behaviour separately so you can reference it later
var zoomObj = d3.behavior.zoom().scaleExtent([1, 8]).on("zoom", zoom);
var canvas = d3.select("canvas")
.attr("width", width)
.attr("height", height)
.call(zoomObj)
.node().getContext("2d");
function zoom() {
var scale = d3.event.scale;
var e = d3.event,
tx = Math.min (0, Math.max(e.translate[0], width - imgBG.width * e.scale)),
ty = Math.min(0, Math.max(e.translate[1], height - imgBG.height * e.scale));
zoomObj.translate( [tx,ty]); // THIS
canvas.save();
canvas.clearRect(0, 0, width, height);
canvas.beginPath();
canvas.translate(tx, ty);
canvas.scale(scale, scale);
draw();
canvas.restore();
}
...
https://jsfiddle.net/ux7gbedj/1/
Currently in d3 if you have a geoJSON object that you are going to draw you have to scale it and translate it in order to get it to the size that one wants and translate it in order to center it. This is a very tedious task of trial and error, and I was wondering if anyone knew a better way to obtain these values?
So for instance if I have this code
var path, vis, xy;
xy = d3.geo.mercator().scale(8500).translate([0, -1200]);
path = d3.geo.path().projection(xy);
vis = d3.select("#vis").append("svg:svg").attr("width", 960).attr("height", 600);
d3.json("../../data/ireland2.geojson", function(json) {
return vis.append("svg:g")
.attr("class", "tracts")
.selectAll("path")
.data(json.features).enter()
.append("svg:path")
.attr("d", path)
.attr("fill", "#85C3C0")
.attr("stroke", "#222");
});
How the hell do I obtain .scale(8500) and .translate([0, -1200]) without going little by little?
My answer is close to Jan van der Laan’s, but you can simplify things slightly because you don’t need to compute the geographic centroid; you only need the bounding box. And, by using an unscaled, untranslated unit projection, you can simplify the math.
The important part of the code is this:
// Create a unit projection.
var projection = d3.geo.albers()
.scale(1)
.translate([0, 0]);
// Create a path generator.
var path = d3.geo.path()
.projection(projection);
// Compute the bounds of a feature of interest, then derive scale & translate.
var b = path.bounds(state),
s = .95 / Math.max((b[1][0] - b[0][0]) / width, (b[1][1] - b[0][1]) / height),
t = [(width - s * (b[1][0] + b[0][0])) / 2, (height - s * (b[1][1] + b[0][1])) / 2];
// Update the projection to use computed scale & translate.
projection
.scale(s)
.translate(t);
After comping the feature’s bounding box in the unit projection, you can compute the appropriate scale by comparing the aspect ratio of the bounding box (b[1][0] - b[0][0] and b[1][1] - b[0][1]) to the aspect ratio of the canvas (width and height). In this case, I’ve also scaled the bounding box to 95% of the canvas, rather than 100%, so there’s a little extra room on the edges for strokes and surrounding features or padding.
Then you can compute the translate using the center of the bounding box ((b[1][0] + b[0][0]) / 2 and (b[1][1] + b[0][1]) / 2) and the center of the canvas (width / 2 and height / 2). Note that since the bounding box is in the unit projection’s coordinates, it must be multiplied by the scale (s).
For example, bl.ocks.org/4707858:
There’s a related question where which is how to zoom to a specific feature in a collection without adjusting the projection, i.e., combining the projection with a geometric transform to zoom in and out. That uses the same principles as above, but the math is slightly different because the geometric transform (the SVG "transform" attribute) is combined with the geographic projection.
For example, bl.ocks.org/4699541:
The following seems to do approximately what you want. The scaling seems to be ok. When applying it to my map there is a small offset. This small offset is probably caused because I use the translate command to center the map, while I should probably use the center command.
Create a projection and d3.geo.path
Calculate the bounds of the current projection
Use these bounds to calculate the scale and translation
Recreate the projection
In code:
var width = 300;
var height = 400;
var vis = d3.select("#vis").append("svg")
.attr("width", width).attr("height", height)
d3.json("nld.json", function(json) {
// create a first guess for the projection
var center = d3.geo.centroid(json)
var scale = 150;
var offset = [width/2, height/2];
var projection = d3.geo.mercator().scale(scale).center(center)
.translate(offset);
// create the path
var path = d3.geo.path().projection(projection);
// using the path determine the bounds of the current map and use
// these to determine better values for the scale and translation
var bounds = path.bounds(json);
var hscale = scale*width / (bounds[1][0] - bounds[0][0]);
var vscale = scale*height / (bounds[1][1] - bounds[0][1]);
var scale = (hscale < vscale) ? hscale : vscale;
var offset = [width - (bounds[0][0] + bounds[1][0])/2,
height - (bounds[0][1] + bounds[1][1])/2];
// new projection
projection = d3.geo.mercator().center(center)
.scale(scale).translate(offset);
path = path.projection(projection);
// add a rectangle to see the bound of the svg
vis.append("rect").attr('width', width).attr('height', height)
.style('stroke', 'black').style('fill', 'none');
vis.selectAll("path").data(json.features).enter().append("path")
.attr("d", path)
.style("fill", "red")
.style("stroke-width", "1")
.style("stroke", "black")
});
With d3 v4 or v5 its getting way easier!
var projection = d3.geoMercator().fitSize([width, height], geojson);
var path = d3.geoPath().projection(projection);
and finally
g.selectAll('path')
.data(geojson.features)
.enter()
.append('path')
.attr('d', path)
.style("fill", "red")
.style("stroke-width", "1")
.style("stroke", "black");
Enjoy, Cheers
I'm new to d3 - will try to explain how I understand it but I'm not sure I got everything right.
The secret is knowing that some methods will operate on the cartographic space (latitude,longitude) and others on the cartesian space (x,y on the screen). The cartographic space (our planet) is (almost) spherical, the cartesian space (screen) is flat - in order to map one over the other you need an algorithm, which is called projection. This space is too short to deep into the fascinating subject of projections and how they distort geographic features in order to turn spherical into plane; some are designed to conserve angles, others conserve distances and so on - there is always a compromise (Mike Bostock has a huge collection of examples).
In d3, the projection object has a center property/setter, given in map units:
projection.center([location])
If center is specified, sets the projection’s center to the specified location, a two-element array of longitude and latitude in degrees and returns the projection. If center is not specified, returns the current center which defaults to ⟨0°,0°⟩.
There is also the translation, given in pixels - where the projection center stands relative to the canvas:
projection.translate([point])
If point is specified, sets the projection’s translation offset to the specified two-element array [x, y] and returns the projection. If point is not specified, returns the current translation offset which defaults to [480, 250]. The translation offset determines the pixel coordinates of the projection’s center. The default translation offset places ⟨0°,0°⟩ at the center of a 960×500 area.
When I want to center a feature in the canvas, I like to set the projection center to the center of the feature bounding box - this works for me when using mercator (WGS 84, used in google maps) for my country (Brazil), never tested using other projections and hemispheres. You may have to make adjustments for other situations, but if you nail these basic principles you will be fine.
For example, given a projection and path:
var projection = d3.geo.mercator()
.scale(1);
var path = d3.geo.path()
.projection(projection);
The bounds method from path returns the bounding box in pixels. Use it to find the correct scale, comparing the size in pixels with the size in map units (0.95 gives you a 5% margin over the best fit for width or height). Basic geometry here, calculating the rectangle width/height given diagonally opposed corners:
var b = path.bounds(feature),
s = 0.9 / Math.max(
(b[1][0] - b[0][0]) / width,
(b[1][1] - b[0][1]) / height
);
projection.scale(s);
Use the d3.geo.bounds method to find the bounding box in map units:
b = d3.geo.bounds(feature);
Set the center of the projection to the center of the bounding box:
projection.center([(b[1][0]+b[0][0])/2, (b[1][1]+b[0][1])/2]);
Use the translate method to move the center of the map to the center of the canvas:
projection.translate([width/2, height/2]);
By now you should have the feature in the center of the map zoomed with a 5% margin.
There is a center() method you can use that accepts a lat/lon pair.
From what I understand, translate() is only used for literally moving the pixels of the map. I am not sure how to determine what scale is.
In addition to Center a map in d3 given a geoJSON object, note that you may prefer fitExtent() over fitSize() if you want to specify a padding around the bounds of your object. fitSize() automatically sets this padding to 0.
I was looking around on the Internet for a fuss-free way to center my map, and got inspired by Jan van der Laan and mbostock's answer. Here's an easier way using jQuery if you are using a container for the svg. I created a border of 95% for padding/borders etc.
var width = $("#container").width() * 0.95,
height = $("#container").width() * 0.95 / 1.9 //using height() doesn't work since there's nothing inside
var projection = d3.geo.mercator().translate([width / 2, height / 2]).scale(width);
var path = d3.geo.path().projection(projection);
var svg = d3.select("#container").append("svg").attr("width", width).attr("height", height);
If you looking for exact scaling, this answer won't work for you. But if like me, you wish to display a map that centralizes in a container, this should be enough. I was trying to display the mercator map and found that this method was useful in centralizing my map, and I could easily cut off the Antarctic portion since I didn't need it.
To pan/zoom the map you should look at overlaying the SVG on Leaflet. That will be a lot easier than transforming the SVG. See this example http://bost.ocks.org/mike/leaflet/ and then How to change the map center in leaflet
With mbostocks' answer, and Herb Caudill's comment, I started running into issues with Alaska since I was using a mercator projection. I should note that for my own purposes, I am trying to project and center US States. I found that I had to marry the two answers with Jan van der Laan answer with following exception for polygons that overlap hemispheres (polygons that end up with a absolute value for East - West that is greater than 1):
set up a simple projection in mercator:
projection = d3.geo.mercator().scale(1).translate([0,0]);
create the path:
path = d3.geo.path().projection(projection);
3.set up my bounds:
var bounds = path.bounds(topoJson),
dx = Math.abs(bounds[1][0] - bounds[0][0]),
dy = Math.abs(bounds[1][1] - bounds[0][1]),
x = (bounds[1][0] + bounds[0][0]),
y = (bounds[1][1] + bounds[0][1]);
4.Add exception for Alaska and states that overlap the hemispheres:
if(dx > 1){
var center = d3.geo.centroid(topojson.feature(json, json.objects[topoObj]));
scale = height / dy * 0.85;
console.log(scale);
projection = projection
.scale(scale)
.center(center)
.translate([ width/2, height/2]);
}else{
scale = 0.85 / Math.max( dx / width, dy / height );
offset = [ (width - scale * x)/2 , (height - scale * y)/2];
// new projection
projection = projection
.scale(scale)
.translate(offset);
}
I hope this helps.
For people who want to adjust verticaly et horizontaly, here is the solution :
var width = 300;
var height = 400;
var vis = d3.select("#vis").append("svg")
.attr("width", width).attr("height", height)
d3.json("nld.json", function(json) {
// create a first guess for the projection
var center = d3.geo.centroid(json)
var scale = 150;
var offset = [width/2, height/2];
var projection = d3.geo.mercator().scale(scale).center(center)
.translate(offset);
// create the path
var path = d3.geo.path().projection(projection);
// using the path determine the bounds of the current map and use
// these to determine better values for the scale and translation
var bounds = path.bounds(json);
var hscale = scale*width / (bounds[1][0] - bounds[0][0]);
var vscale = scale*height / (bounds[1][1] - bounds[0][1]);
var scale = (hscale < vscale) ? hscale : vscale;
var offset = [width - (bounds[0][0] + bounds[1][0])/2,
height - (bounds[0][1] + bounds[1][1])/2];
// new projection
projection = d3.geo.mercator().center(center)
.scale(scale).translate(offset);
path = path.projection(projection);
// adjust projection
var bounds = path.bounds(json);
offset[0] = offset[0] + (width - bounds[1][0] - bounds[0][0]) / 2;
offset[1] = offset[1] + (height - bounds[1][1] - bounds[0][1]) / 2;
projection = d3.geo.mercator().center(center)
.scale(scale).translate(offset);
path = path.projection(projection);
// add a rectangle to see the bound of the svg
vis.append("rect").attr('width', width).attr('height', height)
.style('stroke', 'black').style('fill', 'none');
vis.selectAll("path").data(json.features).enter().append("path")
.attr("d", path)
.style("fill", "red")
.style("stroke-width", "1")
.style("stroke", "black")
});
How I centered a Topojson, where I needed to pull out the feature:
var projection = d3.geo.albersUsa();
var path = d3.geo.path()
.projection(projection);
var tracts = topojson.feature(mapdata, mapdata.objects.tx_counties);
projection
.scale(1)
.translate([0, 0]);
var b = path.bounds(tracts),
s = .95 / Math.max((b[1][0] - b[0][0]) / width, (b[1][1] - b[0][1]) / height),
t = [(width - s * (b[1][0] + b[0][0])) / 2, (height - s * (b[1][1] + b[0][1])) / 2];
projection
.scale(s)
.translate(t);
svg.append("path")
.datum(topojson.feature(mapdata, mapdata.objects.tx_counties))
.attr("d", path)
I have a zoom event handler on my tree graph like so:
d3.select("#"+canvasId+" svg")
.call(d3.behavior.zoom()
.scaleExtent([0.05, 5])
.on("zoom", zoom));
Which calls the zoom function which handles the translation bounding logic:
function zoom() {
console.log(d3.event.translate[0]);
var wcanvas = $("#"+canvasId+" svg").width();
var hcanvas = $("#"+canvasId+" svg").height();
var displayedWidth = w*scale;
var scale = d3.event.scale;
var h = d3.select("#"+canvasId+" svg g").node().getBBox().height*scale;
var w = d3.select("#"+canvasId+" svg g").node().getBBox().width*scale;
var padding = 100;
var translation = d3.event.translate;
var tbound = -(h-hcanvas)-padding;
var bbound = padding;
var lbound = -(w-wcanvas)-padding;
var rbound = padding;
// limit translation to thresholds
translation = [
Math.max(Math.min(translation[0], rbound), lbound),
Math.max(Math.min(translation[1], bbound), tbound)
];
console.log("Width: "+w*scale+" || Height: "+h*scale+" /// "+"Left: "+translation[0]+" || Top: "+translation[1]);
d3.select("#"+canvasId+" svg g")
.attr("transform", "translate(" + translation + ")" +" scale(" + scale + ")");
console.log(d3.select("#"+canvasId+" svg g")[0]);
}
However, translations beyond the bounds cause the d3.event.translate values to increase. The result is that even if the translation is not causing the graph to move as it has reached its limit for translation, the value for the translation within successive events can continue to increase.
The result is that say I drag the graph far to the left, even though it will stop moving past a certain point, because the value within the events continues to increase, I would then have to drag it a long way back right before it actually begins to move right again.
Is there a good way to prevent this behaviour?
Okay I worked it out. The trick is to set the translation for the d3.behaviour.zoom so that successive zoom pans start at the bounded translation rather than with the additional panning that didn't actually give any movement.
To do this, we declare the zoom behaviour as a separate variable and add it to our zoomable element:
var zoomBehaviour = d3.behavior.zoom()
.scaleExtent([0.05, 5])
.on("zoom", zoom)
d3.select("#"+canvasId+" svg")
.call(zoomBehaviour);
Then we set the translation of this zoomBehaviour to our bounded translation in the zoom function:
function zoom() {
...
translation = [
Math.max(Math.min(translation[0], rbound), lbound),
Math.max(Math.min(translation[1], bbound), tbound)
];
zoomBehaviour.translate(translation);
d3.select("#"+canvasId+" svg g")
.attr("transform", "translate(" + translation + ")" +" scale(" + scale + ")");
}
Im using d3.js zoom function to zoom in on an image inside an svg. Im using a mask to reveal an underlying image beneath. If i dont zoom the mask and mouse cursor coordinates match up perfectly. However, when i start to zoom the mouse coordinates are not translating to the zoom level, thus the map reveal is not lining up with the cursor anymore.
here is what im using so far...Im assuming there needs to be some sort of coordinate translation when zooming?
var lightMap = d3.select("#lightMap").call(d3.behavior.zoom().scaleExtent([1, 3]).on("zoom", zoom));
var darkMap = d3.select("#darkMap").call(d3.behavior.zoom().scaleExtent([1, 3]).on("zoom", zoom));
function zoom() {
lightMap.attr("transform", "translate(" + d3.event.translate + ")scale(" + d3.event.scale + ")");
darkMap.attr("transform", "translate(" + d3.event.translate + ")scale(" + d3.event.scale + ")");
}
var svg = d3.select("svg");
svg.on('mousemove', function () {
var coordinates = [0, 0];
coordinates = d3.mouse(this);
var x = coordinates[0];
var y = coordinates[1];
primaryCircle.setAttribute("cy", y + 'px');
primaryCircle.setAttribute("cx", x + 'px');
});
(I know this is a late answer but I had the same problem and thought I'd share how I fixed it for future people who see this)
Fix: Use coordinates=mouse(lightMap.node()) / darkMap.node() instead of mouse(this). Alternatively, and probably more correctly, call the zoom behavior on svg and keep using mouse(this).
Explanation: You call the mousemove function on svg, so mouse(this) gets the coordinates within the svg element. However you don't apply the zoom behavior to svg, so you get wrong coordinates. Call mouse(_) on an element that zooms.
I am trying to implement a simple zoom in d3.js, simpler than all the examples I have gone through (I suppose) but it just doesn't wanna work. So, the functionality that I want to implement is: the user clicks on a section of the graph and that section zooms at a predefined fixed size in the centre of the chart; the user cannot zoom it any further, no panning either. And when the user clicks at any other section of the chart, the zoomed section translates back to its normal/original position.
var container = svg.append("g").classed("container-group", true);
container.attr({transform: "translate(" + 40*test_data.row + "," + 40*test_data.col + ")"});
container.call(d3.behavior.zoom().scaleExtent([1,5]).on("zoom", zoom));
function zoom() {
container.attr("transform","translate(" + d3.event.translate + ")scale(" + d3.event.scale + ")");
}
I have tried zoom.translate and zoom.size but couldn't get them right. And don't know how to reset the zoomed section either.
Any help would be much appreciated !
I´ll give an example of zooming some circles. Clicking on the red rectangle will zoom out to 50%, clicking on the blue one will return to a 100% scale. The exact functions you are looking for are zoomOut() and initialZoom()
var zoomListener = d3.behavior.zoom().scaleExtent([0.1, 3]);
width = 200 ;
height = 200 ;
//svg
var svg = d3.select("body").append("svg").attr("id","vis")
.attr("width", width )
.attr("height", height );
//transition listener group
var svgGroup = svg.append("g").call(zoomListener);
//zoom in and zoom out buttons
svg.append("rect").attr("x",0).attr("y",0).attr("width",50).attr("height",50).style("fill","red").on("click",zoomOut);
svg.append("rect").attr("x",0).attr("y",50).attr("width",50).attr("height",50).style("fill","blue").on("click",initialZoom);
var i,k;
for(i=90;i<width-20;i+=20){
for( k=20;k<height-20;k+=20){
svgGroup.append("circle").attr("cx", i).attr("cy", k).attr("r", 10);
}
}
function zoomOut(){
//fix transition to center of canvas
x = (width/2) * 0.5;
y = (height/2) * 0.5;
//zoom transition- scale value 150%
svgGroup.transition().duration(500).attr("transform", "translate("+x+","+y+")scale(0.5)" );
}
function initialZoom(){
//fix transition to center of canvas
x = (width/2) ;
y = (height/2) ;
//zoom transition- scale value 100%
svgGroup.transition().duration(500).attr("transform", "scale(1)" );
}