Hi, Mattica:
You can try the following OC code:
#define STR_HEATMAP_TEMPLATE "heatmap.otp"
void test_CreateHeatMap()
{
//create graph from template and get first layer to add plot
GraphPage gp;
gp.Create(STR_HEATMAP_TEMPLATE);
GraphLayer gl = gp.Layers(0);
//prepare data for plot
MatrixLayer ml("[MBook1]");
MatrixObject mo(ml, 0);
//plot data on graph layer.
gl.AddPlot(mo, IDM_PLOT_CONTOUR);
return;
}