I found two methods. It seems that 1. is used more broadly. But I think 2. is simpler.


1. a method: refer to

http://www.treeofwords.com/kalu/Access?accessedID=11864

2. another method:
Interactive SVG on the iPad
(I tested the sample of the page on my iPad with iOS 6 and iPhone 4 with iOS 7 and it worked well.
But I am not sure if those codes work when used in iOS apps not just in web apps.)

http://techblog.floorplanner.com/post/20528546052/interactive-svg-on-the-ipad

var x;
var y;
var touchX;
var touchY;
var width;
var height;
var rotation = 0;
var handlingGesture = false;

function touchStart(event) {
event.preventDefault();

if(!handlingGesture) {
// one finger touch => start drag
if(event.touches.length == 1) {
var touch = event.touches[0];
var node = touch.target;

x = parseInt(node.getAttributeNS(null, 'x'));
y = parseInt(node.getAttributeNS(null, 'y'));

touchX = touch.pageX;
touchY = touch.pageY;
}
}
}

function touchMove(event){
event.preventDefault();

if(!handlingGesture) {
// one finger touch => drag
if(event.touches.length == 1) {
var touch = event.touches[0];
var node = touch.target;

var dx = touch.pageX - touchX;
var dy = touch.pageY - touchY;

var newX = x + dx;
var newY = y + dy;

// set rotation to 0 before moving
setRotation(node, 0, newX+width/2, newY+height/2);

node.setAttributeNS(null, 'x', newX);
node.setAttributeNS(null, 'y', newY);

// restore rotation
setRotation(node, rotation, newX+width/2, newY+height/2);
}
}
}

function touchEnd(event) {
if(event.touches.length == 0) {
handlingGesture = false;
}
}

function gestureStart(event) {
event.preventDefault();
handlingGesture = true;
var node = event.target;

x = parseInt(node.getAttributeNS(null, 'x'));
y = parseInt(node.getAttributeNS(null, 'y'));

width = parseInt(node.getAttributeNS(null, 'width'));
height = parseInt(node.getAttributeNS(null, 'height'));

var transform = (node.getAttributeNS(null, 'transform'));
rotation = parseInt(transform.split('rotate(')[1].split(' ')[0]); // ouch

if(isNaN(rotation)) {
rotation = 0;
}
}

function gestureChange(event) {
event.preventDefault();
var node = event.target;

// scale
var newWidth = width * event.scale;
var newHeight = height * event.scale;

var newX = x - (newWidth - width)/2;
var newY = y - (newHeight - height)/2;

node.setAttributeNS(null, 'width', newWidth);
node.setAttributeNS(null, 'height', newHeight);
node.setAttributeNS(null, 'x', newX);
node.setAttributeNS(null, 'y', newY);

// rotation
var newRotation = rotation + event.rotation;
var centerX = newX + newWidth/2;
var centerY = newY + newHeight/2;
setRotation(node, newRotation, centerX, centerY);
}

function gestureEnd(event) {
rotation = rotation + event.rotation;
}

function setRotation(node, rotation, x, y) {
var centerX = x + width/2;
var centerY = y + height/2;

node.setAttributeNS(null, 'transform', 'rotate('+ rotation +' '+ x +' '+ y +')');
}