Pre-allocating geoshape array

Hi,

I am tring to concatenate a geoshape array in the follwoing manner:

finalShape = geoshape();

for k=1:nodeCount
    %some code here...
    m_shape = struct('Geometry', 'line','Longitude', str2double (x), 'Latitude', str2double (y));
    m_shape_geo = geoshape(m_shape);
    %some code here...(adds m_shape_geo adiditonal data)
    finalShape = vertcat(finalShape, m_shape_geo);
end

This is very slow funciton, I belive due to missing preallocating.

1. How do I pre allocate finalshape?
2. Any other\better way to add geoshapes to array?

Thanks,

Yoni