GPR can detect ceramic, concrete, plastic pipes and conduits which would otherwise require tracer wire or sondes using EM locator. This ensures accurate location of all the utilities in your project. Using GPR gives a peace of mind to you while conducting your project knowing any type of utilities will be detected, marked and avoided.
Magnetic Locator (ML) helps locate metal objects that are passive and might be hard to detect by either the GPR or EM. Oil tanks will be the best example where ML will be used to locate the tank and the GPR will be used to confirm the reading to have the best result of both.
Electro-magnetic Locator (EM) helps locate underground utilities and is very helpful in looking for gas, hydro, communication cables and TV cables to avoid damage during excavation or drilling. EM locators are often used because they can detect utility lines and other resources buried under non-magnetic material including snow, water and plastic just accurately as they can through dirt or concrete. EM is portable and can sometimes outperform the GPR in certain conditions.