Transformation of Coordinates Question

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Hello all,

I am trying to transform between my Kinect's /camera_depth_optical_frame and my robot's /base_link frame. I have an Eigen::Vector4f which contains a position (x,y,z) of my point cloud in the Kinect's frame but to use the inverse kinematics services I need to transform this into the /base_link coordinate system.

Using tf_echo I know the position/rotation transformation between these two links, I just need to physically change the x,y,z values into other x,y,z values. Does anyone know a way to do this?

EDIT: Using Ivan's answer I have updated my code but get different errors now.

Here is what I have outputting to the console:

[ INFO] [1361845870.463119633, 1361845870.461467027]: Centroid of cloud cluster is: (-0.049989, 0.026934, 0.519591)
[ WARN] [1361845870.466575058, 1361845870.461467027]: Base to camera transform unavailable Frame id /base_link does not exist! Frames (1): 
[ INFO] [1361845870.466641668, 1361845870.461467027]: 40837646868892605535297603077151234559928972087249378994085663878457812789968315215666377820143542193373920416857156869752951414053701443003877027669632883493287576239311400849870068362363273131362348953463857542966647618830627681059177758720.000000 -0.000000 0.000000

The code that corresponds to this output is:

Eigen::Vector4f centroid; 

pcl17::compute3DCentroid(*cloud_cup,centroid);
pcl17::PointCloud<pcl17::PointXYZRGB>::Ptr cloud_cent (new pcl17::PointCloud<pcl17::PointXYZRGB>);
ROS_INFO("Centroid of cloud cluster is: (%f, %f, %f)",centroid[0],centroid[1],centroid[2]);

cloud_cent->points.resize(1);
cloud_cent->points[0].x = centroid[0];
cloud_cent->points[0].y = centroid[1];
cloud_cent->points[0].z = centroid[2];


tf::Vector3 point(centroid[0],centroid[1],centroid[2]);

tf::TransformListener listener;
tf::StampedTransform transform;
try{
    listener.lookupTransform("/base_link", "/camera_depth_optical_frame",  
                    ros::Time::now(), transform);
    }
catch (tf::TransformException ex){
    ROS_WARN("Base to camera transform unavailable %s", ex.what());
    }

tf::Vector3 point_bl = transform * point;

ROS_INFO("%f %f %f", point_bl[0],point_bl[1],point_bl[2]);

So it says my transformation doesn't exist but in my .urdf I have defined the joint from the base_link to the camera_link. When I run tf tf_echo /base_link /camera_depth_optical_frame I get an output of:

rosrun tf tf_echo /base_link /camera_depth_optical_frame
Failure at 1361845642.173521041
Exception thrown:Frame id /camera_depth_optical_frame does not exist! Frames (17): Frame /camera_link exists with parent /base_link.
Frame /base_link exists with parent NO_PARENT.
Frame /head_link exists with parent /base_link.
Frame /left_rotator_link exists with parent /left_shoulder_link.
Frame /left_shoulder_link exists with parent NO_PARENT.
Frame /left_upper_bicep_link exists with parent /left_tricep_link.
Frame /left_tricep_link exists with parent NO_PARENT.
Frame /left_lower_forearm_link exists with parent /left_upper_forearm_link.
Frame /left_upper_forearm_link exists with parent NO_PARENT.
Frame /right_rotator_link exists with parent /right_shoulder_link.
Frame /right_shoulder_link exists with parent NO_PARENT.
Frame /right_upper_bicep_link exists with parent /right_tricep_link.
Frame /right_tricep_link exists with parent NO_PARENT.
Frame /right_lower_forearm_link exists with parent /right_upper_forearm_link.
Frame /right_upper_forearm_link exists with parent NO_PARENT.
Frame /stand_link exists with parent /base_link.

The current list of frames is:
Frame /camera_link exists with parent /base_link.
Frame /base_link exists with parent NO_PARENT.
Frame /head_link exists with parent /base_link.
Frame /left_rotator_link exists with parent /left_shoulder_link.
Frame /left_shoulder_link exists with parent NO_PARENT.
Frame /left_upper_bicep_link exists with parent /left_tricep_link.
Frame /left_tricep_link exists with parent NO_PARENT.
Frame /left_lower_forearm_link exists with parent /left_upper_forearm_link.
Frame /left_upper_forearm_link exists with parent NO_PARENT.
Frame /right_rotator_link exists with parent /right_shoulder_link.
Frame /right_shoulder_link exists with parent NO_PARENT.
Frame ...