How tweens matrices between keyframes CSS are made?

How can you change the way make use keyframes when transformatrix to perform, in a circular interpolation matrix? the movement made from one keyframe to another does not guara the center even if they are closely spaced keifrnames

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 <g id="todo"> 
 <defs>
    <style type="text/css"> 
.a1621{
                        animation-duration:35s;
                      animation-iteration-count: 1;
                      animation-direction: normal;
                animation-play-state:running;
                animation-name:a1621;
 transform-origin:0px 0px 0px ;

                    }

                @keyframes a1621  
                        {
                        0% {


        transform: matrix3d(1.94872,0,0,0,0,1.94872,0,0,0,0,1.94872,0,-354.819,-265.641,0,1);

     }
     100% {



        transform: matrix3d(1.17277,1.55632,0,0,-1.55632,1.17277,0,0,0,0,1.94872,0,371.155,-630.437,0,1);

     }}</style> </defs> 


                     <g id="1621">    <g fill="" stroke="" stroke-width="" name="draga" id="Rectangulo1621" class="a1621" 
style="transform: matrix3d(1.9487160000000001,0,0,0,0,1.9487160000000001,0,0,0,0,1.9487160000000001,0,-354.819344,-265.64068,0,1)"> <g>
                    <rect  stroke="none" stroke-width="" x="324" y="250" width="100" height="60"></rect>
</g></g></g>                                                              
 <g id="1622">   <g fill="" stroke="" stroke-width="" name="draga" id="Rectangulo1622" class="a1622" 

 style="transform: matrix3d(1.1727689719168597,1.5563169911393604,0,0,-1.5563169911393604,1.1727689719168597,0,0,0,0,1.94872,0,371.1554420221154,-630.4372668228414,0,1)"> <g>
                    <rect  fill="rgb(4, 180, 95)" stroke="none" stroke-width="" x="324" y="250" width="100" height="60"></rect>
 </g></g></g>                                                              

</g>                     
  </svg>    

http://codepen.io/mateos1/pen/mEVomZ foo