hector slam launch with odom and hokuyo

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Hi,

I'm trying to use hector mapping on my custom robot to produce a map, this works fine without any odometry information from my odom node.

here's the launch file (i didn't write it, but it works pretty well).

<node pkg="hector_mapping" type="hector_mapping" name="hector_mapping"    output="screen">

<param name="pub_map_odom_transform" value="true"/>
<param name="map_frame" value="map" />
<param name="base_frame" value="base_link" />
<param name="odom_frame" value="base_link" />
<!-- Map size / start point -->
<param name="map_resolution" value="0.025"/>
<param name="map_size" value="2048"/>
<param name="map_start_x" value="0.5"/>
<param name="map_start_y" value="0.5" />
<param name="laser_z_min_value" value="-2.5" />
<param name="laser_z_max_value" value="7.5" />

<!-- Map update parameters -->
<param name="update_factor_free" value="0.4"/>
<param name="update_factor_occupied" value="0.7" />    
<param name="map_update_distance_thresh" value="0.2"/>
<param name="map_update_angle_thresh" value="0.06" />
</node>

<node pkg="tf" type="static_transform_publisher" name="base_to_laser_broadcaster"      args="0 0 0 0 0 0 /base_link /laser 100" />  

</launch>

The problem is when i try and use it with my odometry information, published from my odom node (which has the same framework as the one from the odom tutorial, but is customised to take my encoder data and use my equations) -

#include <ros/ros.h>
#include <tf/transform_broadcaster.h>
#include <nav_msgs/Odometry.h>
#include <std_msgs/Float32.h> 
#include <math.h>

#define RovWid 0.25
#define Pi 3.141592865358979
#define TicksPerRev 600
#define WheelDia 0.13

float left,right; //declare global variables to hold incoming data

void CallbackLeft(const std_msgs::Float32::ConstPtr& msg)
{
  //ROS_INFO("Left ticks [%f]", msg->data);
  left = msg->data;
}

void CallbackRight(const std_msgs::Float32::ConstPtr& msg)
{
  //ROS_INFO("Right ticks [%f]", msg->data);
  right = msg->data;
}

int main(int argc, char** argv){
    ros::init(argc, argv, "odometry_publisher");

    ros::NodeHandle n;
    ros::Publisher odom_pub = n.advertise<nav_msgs::Odometry>("odom", 50);
    ros::Subscriber sub1 = n.subscribe("ticks_left", 100, CallbackLeft);
    ros::Subscriber sub2 = n.subscribe("ticks_right", 100, CallbackRight);
    tf::TransformBroadcaster odom_broadcaster;

    double vx = 0.0;
    double vy = 0.0;
    double vth = 0.0;

    float DeltaLeft = 0;
    float DeltaRight = 0;
    float PreviousRight = 0;
    float PreviousLeft = 0;

    float Theta = 0;
    float X = 0;
    float Y = 0;

    float Circum, DisPerTick, expr1,right_minus_left;

    ros::Time current_time, last_time;
    current_time = ros::Time::now();
    last_time = ros::Time::now();

    ros::Rate r(5);
    ROS_INFO("Node started");
    Circum = Pi * WheelDia;
    DisPerTick = Circum / TicksPerRev;

    while(n.ok()){

          ros::spinOnce();               // check for incoming messages
          current_time = ros::Time::now();

          DeltaRight = (right - PreviousRight) * DisPerTick;
          DeltaLeft = (left - PreviousLeft) * DisPerTick;
          PreviousRight = right;
          PreviousLeft = left;


          if (DeltaLeft == DeltaRight){
                X += DeltaLeft * cos(Theta);
                Y += DeltaLeft * sin(Theta);
          }
          else{
                 expr1 = RovWid * 2 * (DeltaRight + DeltaLeft)/ 2.0 / (DeltaRight - DeltaLeft);
                 right_minus_left = DeltaRight - DeltaLeft;
                 X += expr1 * (sin(right_minus_left / (RovWid *2) + Theta) - sin(Theta));
                 Y -= expr1 * (cos(right_minus_left / (RovWid *2) + Theta) - cos(Theta));
                 Theta += right_minus_left / (RovWid *2);
                 Theta = Theta - ((2 * Pi) * floor( Theta / (2 * Pi)));
          }

          ROS_INFO("X [%f]", X);
          ROS_INFO("Y [%f]", Y);
          ROS_INFO("Theta [%f]", Theta);
          ROS_INFO("\n");

          geometry_msgs::Quaternion odom_quat = tf::createQuaternionMsgFromYaw(Theta);

          geometry_msgs::TransformStamped odom_trans;
          odom_trans.header.stamp = current_time;
          odom_trans.header.frame_id = "odom";
          odom_trans.child_frame_id = "base_link";

          odom_trans.transform.translation.x = X;
          odom_trans.transform.translation ...