When you are proficient with n4ce and using your own data, this exercise may take literally a matter of seconds. We’re going to work slowly, but you will very quickly see how observations are handled in n4ce and how simple it is to display a reduced survey graphically.
Exercise 1. Processing a Survey File
We’ll be importing survey observations into n4ce from an external LOG file, form a traverse adjustment and display the reduced survey graphically. Other survey file formats are available including DBX (Leica) and EXP (AiC) and XPad Raw.
In n4ce, focus on Observations, right click and Select Import then navigate to the Desktop Icon called n4ce Support Files and select the ..\Training folder. File of type will be LOG by default.
- Highlight the file CPD2.LOG and select Open.
- n4ce will automatically recognise the file format from the header it contains and load the LOG file into the Observations folder, with sub folders for each instrument setup.
- Focus on Observations. This will display a list of available surveys, their source, the number of setups and the data/time they were imported in the right-hand Display Window, as shown below.
- Now focus over the survey AIC_TRAV. n4ce displays information regarding the setups contained within the survey including station name, instrument height, type of observation, number of readings from each station and the last date/time they were edited.
- Move the focus to the folder containing the first setup, Setup A.
This Grid behaves in much the same way as a standard spreadsheet, you can change the entries in cells, group select, cut and paste readings, search and replace etc. The display of observations themselves is hopefully self-explanatory. Each row contains a reading consisting of the standard Code, Number, Tgt Ht etc.…
The Easting, Northing and Height columns are grey and empty. This is because the survey has not yet been reduced.Note: Control observations (back-sight and fore-sight) have a -99 Pnt# reading and are shaded a deep yellow colour. This is so that they may be more easily tracked among the masses of standard observations.
Before moving on make a note of the following:
- Each instrument setup has at least one backsight reading, which is the first reading in the Grid. In the case of a Traverse n4ce assumes foresight as the final control reading in the grid.
- If multiple control readings are taken to a station, n4ce will take the first reading as being on Face Left and reduce the rest of the reading to this station, to this face, then calculate a mean.
- This meaned angle will be used in reductions unless the Average Backsight is unchecked during reductions. In this case, only the first RO reading is used. See later.
- Before we start to process this raw survey data, there are some defaults which it would be prudent to check out.
From the Settings menu select Observations. The Survey Instrument Settings dialog box appears, shown below.
This dialog box allows you to configure n4ce to all possible methods of recording observations in the field. Once set these defaults will not need to be changed.
Errors could ensue if they are altered indiscriminately. Cancel this dialog box.
Select Corrections from the Settings menu. The Survey Observation Corrections dialog box appears, as shown below. Apply corrections with care!
- Before we calculate a traverse or reduce the survey observations, it would be wise to check which corrections n4ce is set up to use.
Three corrections are possible during any adjustment and survey reduction. Only corrections with a ticked box next to them will be applied during these processes, which are:
- OS UTM Scale or fixed Scale Correction.
- Mean Sea Level Correction.
- Curvature and Refraction.
Note: Always check these Settings during Adjustments and Reduction. If you are working with GPS control we would suggest you tick OS UTM scale factor correction if you are working with distances over 0.5km.
Although we won’t use Curvature & Refraction corrections in our calculations, check this box. Once checked, the Curvature and Refraction correction become active, as shown above.
The Earth’s Radius and Coefficient of Refraction are constant in the UK. These constants are used to correct the vertical angle on long sights. Press Cancel to leave the settings as they were.
We can now process the traverse and reduce the observations, to produce point coordinates. Right click over the AIC_TRAV (CPD2) folder and select Traverse. This will start the Traverse Wizard.
The left vertical split windows identify the instrument setups. The exercise is to move setups from the left to right windows, in the order of the traverse.
Note with the BS and icons and buttons it is possible to switch BS and FS readings.
You can process nested traverses by moving individual readings from the left to the right windows using the left < and right > buttons, identifying each traverse separately.
The Auto extract button instructs n4ce to read ahead, threading its way through the traverse matching BS and FS readings until it satisfies a finish criterion or runs out of stations.
If the last FS points to the First Station this creates a Closed or Loop Traverse. If the FS points to a Known Station this creates either a Control or Pipe Traverse. Otherwise Open is assumed.
Pressing the Next button takes us to the Pre-Adjustment stage of the wizard. Positional misclosures are calculated based on the type of traverse and the Start and End coordinates before angle misclosures have been distributed, equally between instrument setups.
Enter new values for Station A (1000, 2000, 100) using the TAB key to move between fields and see the pre-adjusted coordinates change. Set the Bearing to 45.0000. This is between the 1st and last Stations.
Note: Angles are DEG.MMSS and not decimal degrees.
Press Next to enter the final stage in the Traverse Wizard and selecting the method of adjustment. Bowditch and Transit are supported.
A full least square variation of coordinates option is available. Also, look for the GPS Link Traverse. Results of the traverse calculation are displayed in a table and can be displayed in a Report later. Three reduction options are available, simply check the most appropriate.
The Traverse Report will summarise how the survey observations are used in calculations. You will note in the example here that multiple sightings are meaned, with the spread of Hz Angles shown in brackets. See below.
Having completed the Traverse calculations, the process enters the Reduction mode.
The Reduction Dialog Box shows a summary of each instrument setup and reports on their Status. An RO Review provides a comparison between the Final Coordinates and those calculated from RO Readings.
These differences are also compared to Tolerances and flagged in the Status. A warning will be given if these are exceeded.
Note: There are three check options, bottom right. These include Reporting, Averaging BS and Reducing Derived stations.
- If Average BS is not checked only the first RO reading will be used in reduction calculations as opposed to a mean of multiples.
- If Reduced Derived is checked any forward or side shots to stations will be ignored and will not appear in the Stations folder.
An iterative reduction process is used that forward calculates station coordinates, before they are needed. This helps where stations setups are occupied before they are referenced. If Reduced Derived is not checked then this iterative process is not applied.
If station Status is Unknown the OK button will be greyed out and you will not be allowed to continue.
The Status will be acted upon as follows:
- Known stations have been manually entered in the Stations
- Adjusted stations are those whose co-ordinates have been calculated as part of a traverse adjustment.
- Derivable stations can be deduced from Known or Adjusted In this survey I2 is such a station. It is derivable because it was taken as a control shot from A, which is a known station.
- Unknown are stations for which n4ce has no information regarding their position, thus preventing a successful reduction.
To complete the reduction process, press the OK button.
Move the focus to Station A on the Project Tree. The Display Window will now show coordinates in the grey area of the grid. Editing the observations will ripple through and update these coordinate values.
Note Items is grey cells can't be edited directly, but can if you right click over the row and select Properties.
n4ce has also amended the Stations folder to reflect the results of the traverse adjustment. The grid view will change to that shown below.
Cells whose values are either Derived or Adjusted are shaded grey to signify that they may not be directly edited. In other words, n4ce is preserving the traverse connecting the stations together. Only those cells shaded magenta may be manually edited.
Note If the magenta cells are edited however, then the Traverse and or Reduction must be regenerated. There is no ripple through effect here.
The next stage then is to view the survey graphically. Focus the folder containing the survey AIC_TRAV and select a graphics Icon. A picture of the survey will now appear, centred and based on its extents. To change the background colour to white press Background Icon.
A special Icon bar has been provided for Display. It includes options to turn the background colour from black to white, tool tips, show complex lines as solid lines, show real point sizes, text displays, stations, control legs and radials. See later.
This graphics “Quick View” allows you to explore the survey, using the Query Icons. These are found in the Query Icon Bar and Query menu.
Query Distance between Points, and
The Zoom Icon bar has numerous options for turning layers on/off, redraw, extents, zooming and panning. A zoom history is also here. Hot keys for zooming are identified in the Zoom menu.
The last icon on the Display Icon bar will show radial lines, in different colours, identifying the station source and detail surveyed.
Individual station radials can be displayed be selecting station from the Display Window, as shown below.
The Icons with a T control the display of text, from none to boxed outlines to save time with redraws. Some text is drawn in integer units so what you see on the screen may not translate in plots or a AutoCAD DWG/DXF file.
As you zoom in you may see the text jump in size. The boxed viewing options can help here as they display the correct size. It’s particularly useful when plotting Tables to see if the text fits withing defined margins.
Whilst on the question of text, be aware that the text is drawn at real size, in mm to whatever object scale you are using for a graphics view. This scale is shown in the Zoom icon bar. In the View menu or by pressing hot keys [ALT]+[V]. AutoCAD uses ground units so this scale is important when transferring between n4ce and AutoCAD, using either DXF or DWG.
Summary of Exercise 1
To recap briefly on what we have learned during this exercise.
The Project Manager has been used to import and present a LOG file, containing raw survey data in Hz Angle, Vt Angle and Sl Distance format. By using different points of focus on the Project Tree, different presentations of data were seen.
A traverse was extracted from control data stored in the survey. Control is highlighted with a -99-point number, with a BS at the beginning of a set of observations and a FS as the last reading in an Observations Grid.
A Traverse Wizard was used to process control stations. Prior to reducing the survey, reference was made to Observation and Correction Defaults. The Status of Stations was discussed.
The survey was viewed both in grid (spread sheet) and graphics form with reduced coordinates. We call this Duality of Display and Edit. n4ce can edit and display data in either grid format or graphically, with updates to the complimentary view.
Not fully discussed but highlighted here are the Query options. The Query Point option can be used as a mini editor, allowing changes to ANYTHING that appears in a white background. This is really useful for adding and editing point attributes.
Finally, greyed off items are tied to other processes and can’t be edited directly. If you want to change items here, you must use the Properties option. The example shown here is for Station Coordinates.
Changing Properties of Stations
Features shown here in graphics come from coded points related to the Survey Code Table which is discussed later.