There are many measuring methods, such as "triangle midline", "triangle congruence", "triangle similarity" and "constructing right triangle", as long as:

(1) Write the measurement method, which is accurate and concise.

(2) draw a chart, correct,

③ The solving or proving process is complete and correct.

Example: use the "triangle midline" ① to determine O that can reach AB at the same time;

(2) take the midpoint m and n of line segment AO and BO and measure the length of line segment MN, then AB=2MN. ..

Congruent triangles's knowledge:

(1) The survey plan is shown in the figure;

(2) First, find a point O outside the lotus pond, connect AO, extend AO to E, so that OE=AO=b meters, connect BC, extend BO to D, make OD=BO=c meters, connect de, and measure DE=a meters;

(3) In △ABO and △EDO, AO=EO, ∠AOB=∠EOD, BO=DO, so △ ABO △ Edo, so AB = DE = one meter.