mesh(Z) by itself uses the row and column index values of Z as the x and y coordinates. Your matrix is [9x19] so the x values are 1:9 and the y values are 1:19.
If you'd like to start at x=-4 and y=-9, you'll need to produce your own X and Y values using meshgrid().
[Xval, Yval] = meshgrid((1:size(th,2))-10, (1:size(th,1))-5);
mesh(Xval, Yval, th);