Advantages and Disadvantage of Total Instrument Operation
Advantages and Disadvantage of Total Instrument Operation
Advantages
-The first advantages is that total station can be a relatively cheap means of fast, high-precision measurements.
-Total station needs line of site, but it does not need visibility of the sky. Total station can be used indoors, in a mine, or under tree cover that would not be suitable for GPS measurement.
-Third, total station is suited to take ground measurements. Whereas GPS is best suited to grid or geodetic measurements, total station is best at ground coordinates. Using GPS to derive ground coordinates (and distance) requires use of an estimated scale factor and a mathematic geoid to approximate distances on the Earth's surface.
-The final advantage to total station is that you don't necessarily need to occupy the point you are trying to measure. Using more advanced functions like offsets, resections, etc. you can measure a point indirectly though combinations of multiple angluar and/or distance measures.
Disadvantage
-Firstly, line of sight is the principle disadvantage to optical measurement. GPS does not need LOS.
-Secondly, (barring use of a robotic system) total station measurement requires at least a two person survey crew. GPS only requires one person to survey.
-Cumulative error is the third disadvantage. Human and machine error is addative with optical work. With each setup and stationing error is imarted to the measurements and subsequent setups and measurements accumulate the errors of previous setups. If you have a 5" gun, as much as 2.5" of angular error is inherent to every shot. The error in gps in not cumulative. Each shot has a "knowable" sphere of error that does not add up from shot to shot to shot.
-The final disadvantage is that measurements are not geodetic. An estimated scale factor and correction for earth curvature is necessary to make measurements relative to the ellipsoid, which is the basis of the UTM/State Plane
Advantages
-The first advantages is that total station can be a relatively cheap means of fast, high-precision measurements.
-Total station needs line of site, but it does not need visibility of the sky. Total station can be used indoors, in a mine, or under tree cover that would not be suitable for GPS measurement.
-Third, total station is suited to take ground measurements. Whereas GPS is best suited to grid or geodetic measurements, total station is best at ground coordinates. Using GPS to derive ground coordinates (and distance) requires use of an estimated scale factor and a mathematic geoid to approximate distances on the Earth's surface.
-The final advantage to total station is that you don't necessarily need to occupy the point you are trying to measure. Using more advanced functions like offsets, resections, etc. you can measure a point indirectly though combinations of multiple angluar and/or distance measures.
Disadvantage
-Firstly, line of sight is the principle disadvantage to optical measurement. GPS does not need LOS.
-Secondly, (barring use of a robotic system) total station measurement requires at least a two person survey crew. GPS only requires one person to survey.
-Cumulative error is the third disadvantage. Human and machine error is addative with optical work. With each setup and stationing error is imarted to the measurements and subsequent setups and measurements accumulate the errors of previous setups. If you have a 5" gun, as much as 2.5" of angular error is inherent to every shot. The error in gps in not cumulative. Each shot has a "knowable" sphere of error that does not add up from shot to shot to shot.
-The final disadvantage is that measurements are not geodetic. An estimated scale factor and correction for earth curvature is necessary to make measurements relative to the ellipsoid, which is the basis of the UTM/State Plane