ShaderTerrainMesh get height position

Hello, i have question, i want to add object in my game with position (x,z)
and i want to have y (height of map) in this location (x,z)

for example i have this terrain :

from panda3d.core import ShaderTerrainMesh, Shader, load_prc_file_data

load_prc_file_data("", "gl-coordinate-system default")
terrain_node = ShaderTerrainMesh()
terrain_node.heightfield_filename = "heightfield.png"
terrain_node.target_triangle_width = 10.0
terrain_np = render.attach_new_node(terrain_node)
terrain_np.set_scale(1024, 1024, 60)
terrain_np.set_shader(Shader.load(Shader.SL_GLSL, "terrain.vert", "terrain.frag"))

i want to add egg object to center of my map, i know x and z (512,512) but i dont know y (height of my map) how can i have this information ?
for example, i want height of position (100,100)
thanks for advance