QA Using LeastSquares Adjustment 
What is a LeastSquares Adjustment ■ When you have multiple (redundant) measurements to compute an unknown value, a leastsquares adjustment might be appropriate to get the best estimate of the unknown value (using all these measurements). ■ For example, when you measure a few time a linear distance, a simple average will provide you the best estimate for this distance. It turns out that this simple average is a leastsquares. ■ In GNSS, when you establish a network of points, you may observe a multiple of vectors connecting all these points, which makes the calculation of the best position for each of these point a complicated task. ■ The leastsquare adjustment is the solution to this problem. 
What is Redundancy in a Network of Vectors? 
LeastSquares Adjustment Parameters Basic parameters of the network adjustment are set under Tools > Options... > Network tab. ■ You can adjust your network through a “Fixed Stations” mode or a “Weighted Stations” mode. To switch between modes, look in the ‘type of adjustment” dropdown list; ■ You can set a confidence level of the error ellipses; ■ Select the representation mode (3D or 1D+2D); ■ You can toggle summary sections to customize the adjustment summary; ■ Finally, you have control on the display of error ellipses in the Plan View (site ellipses or vector ellipses). 
Site Positions before Adjustment Before the adjustment, you have access to a list of all your positions in Analysis > Survey Sites > PostProcessed Coordinates. 
Here is a simple rule to follow when in doubt: the network should be adjusted if the number of new point (unknown point) is less than the number of baselines (excluding vectors between known points), that means a ratio < 1. 
Type of Adjustment
Fixed Station mode Coordinates of reference site (site with known coordinates) are held fixed in the adjustment. The software assumes the coordinates are errorless. If they are not accurate, final positions will be biased (as well as their statistics). You can use as many fixed station as you want.
Note: The following modes are recommended for advanced users only.
Fixed Station with Auxiliary Parameters mode Coordinates of reference sites are held fixed in the adjustment (a minimum of 3 references is required to use this mode). The software assumes the coordinates are errorless. Three rotations and one scale value are estimated along with station coordinates (this information is useful when the reference network is not well aligned WGS84).
Weighted Station mode Coordinates of reference sites are not held fixed in the adjustment. A level of uncertainty is attached to each reference sites to reflect their nonperfect accuracy. This is done through sigmas (standard deviations) that can be entered in the Site Editor (Edit Sigmas). 
Note that the solution type and standard deviations are not displayed if the site is connected to more than one baseline. 
Site Positions after Adjustment After the adjustment, you have access to a list of all your positions in Analysis > Survey Sites > PostProcessed Coordinates. The site standard deviations are now displayed. 
How to Adjust your network Once all your baselines are processed, go to Tools > Process Manual > Adjust Network to adjust your network according to the reference sites used and the selected adjustment parameters. Least squares results can be seen under Analysis > Network Adjustment which gives you access to the Network Adjustment Summary and the Network Adjustment Residuals. 
Article: 000030 Related Products: EZSurv Last Update: 20170330 20:05:44 
Document information 
