Create station errors table

You can use this function to create a station errors table.

There are various reasons why a survey database may not have a station errors table. Perhaps the database had been created without an optional station errors table, or perhaps the station errors table has been deleted. Whatever the reason this function permits you to create a station errors table, to allow you to set up a quality assurance regime for new stations entering the survey database.

Prerequisites: A survey database must be open.

To run this function: Choose Survey > Survey database > Administration > Create station errors table, or...

In the Function Chooser, type CREATE STATION ERRORS TABLE, and press ENTER.

Output

A station errors table is created in the survey database that is open.

If a station errors table already exists, a message informs you of this, and no further action is taken.

More information

Basic concepts

The station errors table is an optional table inside the survey database that allows you to set up a Quality Assurance regime for new stations entering the survey database. You can create rules to determine the order or "quality" of a station (including giving INFORMATIONAL, WARNING or ERROR messages when new stations are created). The system also allows station orders to be propagated, as the particular station is used as a fixed station to calculate a new station, eg if the backsight and setup are both 2nd order then the foresight cannot be created as a new station with an accuracy greater than 2nd order.

The basic concept is that each station is assigned an order value (eg "1st", "2nd", "3rd" etc) which is stored in the station_order field for that station in the survey_stations table in the survey database. The purpose of the station errors table is to allow you to set up very flexible rules to determine how the order value will be assigned for a new station. The station errors table then "watches" all Surpac applications that create new stations, and assigns appropriate new station orders and displays INFORMATIONAL, WARNING or ERROR messages to the user as required. If no station errors table is present in the survey database then all applications proceed exactly as they used to and the station_order field in the survey_stations table is simply not used.

Benefits

The main benefit of using this system is that it gives the Senior Surveyor a lot of control in setting rules to govern the quality of stations entering the survey database. By associating a station order with each new station there is a quantifiable measure of the "quality" of each of the stations in the database. This is useful for audit purposes. The system is very flexible and covers each application function in Surpac that creates new stations.

Features of the system

You can choose order names from a pre-defined picklist ("1st", "2nd", "3rd", "4th", "5th"), or you can make your own names for the orders.
You can choose different actions to assign to the orders:
- CONTINUE Where the station is inserted into the database with no additional feedback to the user.
- INFORMATIONAL Where (in general) a text box with information on the new station order is displayed with an "OK" button to insert the station into the database.
- WARNING Where (in general) a text box with information on the new station order is displayed with an "OK" button to insert the station into the database and a "CANCEL" button to not insert the station into the database.
- ERROR Where (in general) a text box with information on the new station order is displayed with an "OK" button to not insert the station into the database.
You have the option of setting up different "instruments" for which distinct sub-sets of rules apply. For example you can set up different rules for "LEICA1101" or "LEICA1103" instruments. Each Surpac function that creates new stations has a new form-field with a pick list which allows you to choose which instrument you are using for that function. You have total flexibility in defining the instrument names and the rule sub-sets for each instrument.
You can set up station order rules based on:
- Standard deviations for measured horizontal and vertical angles and slope distances; or standard deviations of station coords for resected or survey network adjusted stations. The lower these standard deviations are the more likely you are to have an accurate result.
- Numbers of measured observations. The higher the number of observations, the more trustworthy the result.
- Distance from the setup station to the foresight station (for horizontal and vertical angle and measurements only). It might be the case that an angle measurement error is "large" but because the distance from the setup station to the foresight station is "small" the error does not have a large opportunity to propagate, therefore the new station can still be "accurate". This might be the case in an underground situation with short lines of sight. These values allow you model this situation.
The use of the station errors table is optional. If no station errors table is present in the survey database then all applications proceed exactly as they used to and the station_order field in the survey_stations table is simply not used. However, if a station errors table is present then it will be used. Individual users of the database cannot switch the use of the table on and off as they please. This ensures the integrity of your survey_stations table.

NOTE: As stated earlier, this system supports the propagation of station order values as the station is used as a fixed (eg as a backsight or setup etc) station in the creation of new stations. As a consequence of this it is required that any existing stations in the database that you wish to use for this purpose, must have an order value in their station_order field that is defined in the station_errors table. This is a necessary condition, as the station errors table has to "know" the accuracy of all the fixed stations it is using before it can use them to determine the accuracy of a new station. You will find that if you try to use fixed stations in your database where the order value is unknown to the station errors table, then you will receive warning messages to this effect. This may mean you have to edit some of your historical stations in your database and manually assign them a station_order value before they can be used.

The station errors table is only used when you are creating new stations, if you are just doing a standard pickup and surveying points into a string file then this will work exactly as it did previously (and, for example, the backsight and setup stations you define won't have to have station_order values that are known in the station errors table).

If you have a survey database that doesn't have a station errors table and you want to create one, just go to Survey Survey database Administration - Create station errors table. If you have a survey database that has a station errors table and you want to delete the station errors table, go to Survey - Survey database - Administration - Delete table and select the station errors table.

Technical aspects

There are four generic situations where a station can be created or adjusted in Surpac. These situations each have slightly different values that give the best measurement of the quality of the new station produced. You can set up rules to determine the new station order for each of these four situations. The four cases are:

Creating a station by a standard pickup
Creating a station by resection
Adjusting a station by a 3D survey network adjustment
Adjusting a station by a 2D survey network adjustment

These four cases are discussed individually below:

Creating a station by a standard pickup

This case corresponds to the situation involving a backsight station, a setup station and a foresight station (which becomes the new station). Here one or more of each of the following measurements are made to determine the new station:

horizontal angle measurements
vertical angle measurements
slope distance measurements

For this situation you can set up rules for the new station order based on:

The standard deviation of the horizontal angle measurements. The rule in this case is based on:
- The value of the standard deviation
- The number of horizontal angle measurements taken
- The horizontal distance between the setup and foresight stations. It might be the case that a horizontal angle standard deviation is "large" but because the horizontal distance from the setup station to the foresight station is "small" the error does not have a large opportunity to propagate, therefore the new station can still be "accurate". This might be the case in an underground situation with short lines of sight. Entering this value allows you model this situation.
The standard deviation of the vertical angle measurements. The rule in this case is based on:
- The value of the standard deviation
- The number of vertical angle measurements taken
- The slope distance between the setup and foresight stations. It might be the case that a vertical angle standard deviation is "large" but because the slope distance from the setup station to the foresight station is "small" the error does not have a large opportunity to propagate, therefore the new station can still be "accurate". This might be the case in an underground situation with short lines of sight. Entering this value allows you model this situation.
The standard deviation of the slope distance measurements. The rule in this case is based on:
- The value of the standard deviation
- The number of slope distance measurements taken

It may be the case that you only have one measurement for the horizontal angle and/or the vertical angle and/or the slope distance. If you only have one estimate for a value then you cannot determine a standard deviation for that value. The station errors table accounts for this by allowing you set rules so that instead of basing the order on all three standard deviations, you can just base the order on the standard deviations that can be determined. Alternatively it allows you to set default station order values in this case.

In general the station orders table calculates orders corresponding to the standard deviations (where they exist) of each of the horizontal angle, vertical angle and slope distance measurements and then compares these orders with the orders of the backsight and setup stations. The new station order is then assigned to be the lowest ranking of all these orders. For example, if the backsight and setup stations were "2nd" order and the station errors table determined the standard deviation of the horizontal angle measurements to be "1st" order, the standard deviation of the vertical angle measurements to be "1st" order, and the standard deviation of the slope distance measurements to be "2nd" order, then the new station order would be "2nd" ie the lowest ranking of all these five orders.

The following situations in Surpac where new stations are created correspond to the generic "creating a station by a standard pickup" case:

Data recorder single face pointings to new stations
Data recorder multiface pointings to new stations
Surface traversing
Underground traversing
EDM survey
Stadia survey
Two wire stadia survey
RDS survey

Creating a station by resection

For this situation you can set up rules for the new station order based on:

The value of the x coord standard deviation of the new station
The value of the y coord standard deviation of the new station
The value of the z coord standard deviation of the new station
The number of stations to which resection observations where made (Note: This is the same irrespective of whether you have done a single face or double face resection, eg if you have done a single face resection to three stations or a double face resection to three stations, "the number of stations to which resection observations where made" is still three.)

In general the station orders table calculates orders corresponding to the standard deviations of each of the x, y and z new station coords and then compares these orders with the orders of all the fixed stations in the resection. The new station order is then assigned to be the lowest ranking order of all these orders. For example, if the lowest ranking order of all the fixed stations in the resection was "2nd" and the station errors table determined the standard deviation x station coord to be "1st" order, the standard deviation of the y station coord to be "1st" order, and the standard deviation of the z station coord to be "2nd" order, then the new station order would be "2nd" ie the lowest ranking of all these orders.

Adjusting a station by a 3D survey network adjustment

For this situation you can set up rules for the new station order based on:

The value of the x coord standard deviation of the new station
The value of the y coord standard deviation of the new station
The value of the z coord standard deviation of the new station
The total number of direction, distance, horizontal angle and vertical angle observations that involved that station as a backsight, setup or foresight

In general the station orders table calculates orders corresponding to the standard deviations of each of the x, y and z adjusted station coords and then compares these orders with the orders of all the fixed stations in the adjustment. The new station order is then assigned to be the lowest ranking order of all these orders. For example, if the lowest ranking order of all the fixed stations in the adjustment was "2nd" and the station errors table determined the standard deviation x station coord to be "1st" order, the standard deviation of the y station coord to be "1st" order, and the standard deviation of the z station coord to be "2nd" order, then the new station order would be "2nd" ie the lowest ranking of all these orders.

Adjusting a station by a 2D survey network adjustment

For this situation you can set up rules for the new station order based on:

The value of the x coord standard deviation of the new station
The value of the y coord standard deviation of the new station
The total number of direction, distance and horizontal angle observations that involved that station as a backsight, setup or foresight

In general the station orders table calculates orders corresponding to the standard deviations of each of the x and y adjusted station coords and then compares these orders with the orders of all the fixed stations in the adjustment. The new station order is then assigned to be the lowest ranking order of all these orders. For example, if the lowest ranking order of all the fixed stations in the adjustment was "2nd" and the station errors table determined the standard deviation x station coord to be "1st" order and the standard deviation of the y station coord to be "2nd" order, then the new station order would be "2nd" ie the lowest ranking of all these orders.