protected float getHeightmapHeight(int x, int z) {
        int quad = findQuadrant(x, z);
        int split = (size + 1) >> 1;
        if (children != null) {
            for (int i = children.size(); --i >= 0;) {
                Spatial spat = children.get(i);
                int col = x;
                int row = z;
                boolean match = false;

                // get the child's quadrant
                int childQuadrant = 0;
                if (spat instanceof TerrainQuad) {
                    childQuadrant = ((TerrainQuad) spat).getQuadrant();
                } else if (spat instanceof TerrainPatch) {
                    childQuadrant = ((TerrainPatch) spat).getQuadrant();
                }

                if (childQuadrant == 1 && (quad & 1) != 0) {
                    match = true;
                } else if (childQuadrant == 2 && (quad & 2) != 0) {
                    row = z - split + 1;
                    match = true;
                } else if (childQuadrant == 3 && (quad & 4) != 0) {
                    col = x - split + 1;
                    match = true;
                } else if (childQuadrant == 4 && (quad & 8) != 0) {
                    col = x - split + 1;
                    row = z - split + 1;
                    match = true;
                }

                if (match) {
                    if (spat instanceof TerrainQuad) {
                        return ((TerrainQuad) spat).getHeightmapHeight(col, row);
                    } else if (spat instanceof TerrainPatch) {
                        return ((TerrainPatch) spat).getHeightmapHeight(col, row);
                    }
                }

            }
        }
        return Float.NaN;
    }
This will just get the heightmap value at the supplied point,
not an interpolated (actual) height value.
jme3-terrain/src/main/java/com/jme3/terrain/geomipmap/TerrainQuad.java