$BEG_SKIP ******************************************************************************* Comments can be embedded into the ASCII (Text) data file by either beginning each comment line with an exclamation point (!) or by wrapping one or more comment lines between the $BEG_SKIP and $END_SKIP keywords as is done here. !Example of a single line comment ALL file keywords begin with the dollar sign ($) and are uppercase ******************************************************************************* We have added a new Observation Conversion Tool that can be used to convert Zenith Angles and Chord (slope) Distances to Height Differences and Horizontal Distances. Standard deviations from zenith angles and chord distances are automatically propagated to height difference and horizontal distance standard deviations. One application for this tool is Trig Leveling. In the field you measure zenith angles and slope distance observations, then use this tool to convert them to 1D for vertical adjustments or traversing. TRIG LEVELING: One approach to trig leveling is to set up at an arbitrary position ('Temp1' for example) between a starting benchmark (e.g., 'AA' with known elevation) and the forward station ('BB'). Using the SAME TARGET HEIGHT at station 'AA' and 'BB', you then measure the zenith angle and slope distance to both 'AA' and 'BB' during the same setup at 'Temp1'. Instrument and target heights are not measured, since we are not interested in the elevation of 'Temp1'. Next, you move the instrument to a new arbitrary position between station 'BB' and the next station ('CC' for example) and repeat the process (measure to 'BB', then to 'CC'). This data can be entered into a COLUMBUS compatible ASCII (Text) input file, then loaded into COLUMBUS. At the bottom of this file is a sample set of data for a small Trig Leveling project consisting of a loop traverse. The starting and ending station is 'AA'. Station 'AA' has a known elevation of 170.0 U.S. feet. The elevation for station 'BB', 'CC', and 'DD' are to be determined by the survey. Station 'Temp1', 'Temp2', 'Temp3', and 'Temp4' are the arbitrary instrument setup positions. We are not interested in the elevations of these Temp locations. A Fixed Height target is used on station 'AA', 'BB', 'CC', and 'DD'. For the sample below, the Instrument and Target heights have been set to ZERO. This is due to the fact that a fixed target height was used at station 'AA', 'BB', 'CC', and 'DD'. We don't care about the resulting verticals for the 'Temp#' stations, so we do not need their Instrument Heights. If you did not follow this procedure, you would need to provide an Instrument and Target Height for each set of observations (zenith angle and chord distance). For example, You might have begun your survey by setting up on station 'AA', then measured to station 'BB', then moving forward to 'BB' and measuring to station 'CC', etc. In this scenario, instrument an target heights for all setups must be carefully measured and entered into $AZ_COMPACT records. CONVERTING OBSERVATIONS After loading the observations below into COLUMBUS, enter the TOOLS - CONVERT OBSERVATIONS - ZenCrd --> Vert/Hor Dist Tabbed dialog. Enter the approximate latitude for the project area (47.0 for this example). The Latitude is used to accurately determine corrections due to curvature and deflection of the vertical (if deflection values are provided). An approximate value (+- several minutes) will suffice for most projects. If you have any very long distances, the elevation may come into play. For most projects, a value of 0.0 will be fine. If you want zenith observation corrected for deflection of the vertical, enter the deflection values in seconds. Leaving them set to zero results in no correction. If you wish to correct the zenith angle for refraction, enter the zenith angle refraction coefficient. For information on how refraction is calculated from this coefficient, please refer to the Options chapter of the COLUMBUS user manual. If you want to provide a common Standard Deviation for all zenith angles and/or chord distances (different from what you provided in you input data (see above) then supply a Zenith SD and/or Chord SD. The measured observation SD's (chord and zenith angle) are propagated to the eqivalent Hgt Diff and Hor Dist SD's during computation. Check the "Create Height Diff Obs" checkbox. This Tells COLUMBUS to create this new observation type from the measured observations. Click on the Convert Button and COLUMBUS will present you with a list of all the Zenith Angle and Chord Distances for the current active Datum in the project. NOTE: Your active view should be "1D Vertical". No observation lines (zenith and chord) are shown, because these are not 1D observations types. Select the observations to convert, then click the OK Button. The Height Difference observations will be created and added to the current project. NOTE: The computed height difference observations are now visible in the view. A height difference observation is a valid 1D observation type. At this point you are now ready to use the new height difference observations for a 1D vertical adjustment or a 1D vertical traverse. ADJUSTMENT To perform the adjustment do the following: 1) Enter the "Select Network Stations" dialog and select ALL stations to be included in the adjustment. 2) Enter the "Select Fixed Stations" dialog and select station 'AA' to be fixed in 1D. 3) Enter the "Select Obs" dialog and select ALL observations. 4) Click on the "Start Adjustment" toolbar icon. 5) View your adjusted results by entering the various Results views. NOTE: keep the Network Processing Summary view open. You adjusted height (elevation) for station 'CC' should be 137.4376 U.S. Feet. If U.S. Feet is not the active linear units setting, simply enter the OPTIONS - UNITS dialog and change the linear units to U.S. Feet. The adjusted coordinate view will automatically be updated. This adjustment used observation standard deviations for weighting the adjustment. See the 1D Network Type setting in the OPTIONS - NETWORK OPTIONS - NETWORK SETTINGS tab. Set to 'Standard Deviation Weighted' before performing the adjustment. FINAL NOTES: 1) The results above are based on the following input values when converting the observations to height difference. Latitude: 47.0000 (positive north) Elevation: 0.0 Zenith SD: 0.0 (ignore and use those from input file) Chord SD: 0.0 (ignore and use those from input file) Defl N-S 0.0 (apply no correction) Defl E-W 0.0 (apply no correction) Refrac Coeff 0.0 (apply no correction) 2) Computed height difference observations are automatically corrected for curvature (based on the underlying geodetic model) 3) The computed height difference observation are automatically added to your current project. They have not been saved to disk. To save them to disk with the current project data, invoke the FILE - SAVE or FILE - SAVE AS command. 4) The orginal Zenith and Chord Distances are still in your project. 5) To quickly delete the newly added height difference observations (perhaps you want try adding a refraction correction), follow the steps in number six below, then perform the observation conversion again. 6) Enter the DATA - DELETE OBSERVATIONS dialog. The observations shown are for the current active Datum in the current Project. For Example: To delete one or more height difference observations, click on the Obs Type column to order all observations by observation type. Select the applicable height difference observations (Hgt Diff) to delete, then click on the OK button. Selected observations are deleted from memory only. Your project file will not be changed until you re-save the project. $END_SKIP ! BEGIN PROJECT DATA ************************************************ ! ! ! ! The exact datum used is only important if you are measuring ! long distances, otherwise just about any datum will do. ! NAD 83 parameters $DATUM NAD 83 6378137.000000 298.257222101 ! Linear units in file are in U.S. feet (U, use M if linear units ! are in meters) $UNITS U D 1 ! Opens view in 1D Vertical mode and creates height stations for ! any stations not defined by the $HEIGHT_COMPACT record below. $STATION_TYPE_FOR_OBS 1D_VERT ! Station Names can be a maximum of 15 characters in length ! Station Name; Height; Height SD $HEIGHT_COMPACT; AA; 170.0; 0.00000 ! Global standard deviation for Zenith Angles. This value will ! override any zenith angle standard deviations found in the ! $AZ_COMPACT records below. Remove, comment out, or set to ZERO ! to disable. $G_ZEN_SD 3.0 ! Global standard deviation for Chord (slope) Distances. This ! value will override any chord distance standard deviation found ! in the $AZ_COMPACT records below. Remove, comment out, or set ! to ZERO to disable. $G_CRD_SD 0.010 ! AT Station Name; TO Station Name; Azimuth; Azimuth SD; Zenith; ! Zenith SD; Chord (Slope Dist); Chord SD; Instr Hgt; Targ Hgt $AZ_COMPACT; Temp1; AA; NOOBS; NOOBS; 85.4930; 5.0; 1100.10; 0.015; 0; 0 $AZ_COMPACT; Temp1; BB; NOOBS; NOOBS; 87.1000; 5.0; 1200.30; 0.015; 0; 0 $AZ_COMPACT; Temp2; BB; NOOBS; NOOBS; 86.3015; 5.0; 825.20; 0.015; 0; 0 $AZ_COMPACT; Temp2; CC; NOOBS; NOOBS; 87.4217; 5.0; 965.15; 0.015; 0; 0 $AZ_COMPACT; Temp3; CC; NOOBS; NOOBS; 91.0030; 5.0; 500.10; 0.015; 0; 0 $AZ_COMPACT; Temp3; DD; NOOBS; NOOBS; 93.4320; 5.0; 400.10; 0.015; 0; 0 $AZ_COMPACT; Temp4; DD; NOOBS; NOOBS; 89.3030; 5.0; 650.10; 0.015; 0; 0 $AZ_COMPACT; Temp4; AA; NOOBS; NOOBS; 79.3100; 5.0; 304.25; 0.015; 0; 0 ! ! ! ! END PROJECT DATA ************************************************