What is the difference between a fixed station and a constrained station

How can I fix the latitude or longitude of a station but not both? Use the geodetic coordinate observation. To fix the latitude, set the latitude covariance NN element to be small e. Set the longitude covariance element EE deviation to be large e.

This will allow the longitude the freedom to move, but the latitude will be held virtually fixed. Allow the station, with the same name, to float during the nework adjustment. Can I combine terrestrial measurements observations with GPS and obtain high-quality results?

Terrestrial observations can be as good or better than GPS. One of the greatest advantages of GPS is no traversing is required.

The farther you must traverse in a terrestrial survey, the greater the likelihood for errors to accumulate in your network. However, if you were to measure a network using GPS or terrestrial observations in which no traversing was required, you would soon discover the terrestrial network could be as good or better than the GPS network.

Therefore, you should freely mix GPS and terrestrial measurements as needed. When using terrestrial measurements, be sure to always measure the instrument and target heights at each setup. Also, you may want to experiment with the internal refraction correction or supply zenith angles which already have a built-in correction applied by you.

Where does the number generated come from? The Chi Square Test On Variance Factor is used to test the hypothesis that the a priori variances standard deviation squared for all the observations in the network as a whole are realistic based on the adjustment.

If the a priori variances for all the observations as a whole are in agreement with the adjustment, the A posteriori Variance factor will approach 1. If the interval generated low end below 1. In this case, the A Priori Variance factor would be greater than 1. Whether or not it is significantly greater than 1.

Alternatively, on average, if each observation were adjusted by only 0. Again, whether or not it is significantly less than 1. Why should I be concerned if the a posteriori variance factor is statistically different from 1. The a posteriori variance factor APVF is an indicator for the network as a whole as to the consistency of the adjusted network, given the a priori predicted errors.

The predicted errors are represented by each observation's standard deviation or, in the case of GPS baselines, by the variance covariance matrix for each baseline. If on average, each observation is adjusted by an amount larger than its predicted error, the APVF will tend to be greater than 1. If on average, each observation is adjusted by an amount less than its predicted error, the APVF will tend to be less than 1. In either case, you may not be correctly estimating the quality of your measured observations, or you may have a few bad measurements in your survey those receiving large adjustment.

If the latter is the case, you should attempt to isolate the bad observations and possibly re-measure them, since they may be distorting your results. What is the difference between a Fixed station and a Constrained station? A fixed station is simply a constrained station which is not allowed to move during an adjustment.

In fact, the user could select constrained stations to be fixed stations in the network adjustment if he were to set each station's coordinate component standard deviations to a very small value i. If, however, the user wanted to allow a control station the possibility to move during a network adjustment rarely the case, but some folks insist on it , he would select the station to be constrained. The amount of movement would be constrained not necessarily confined by the standard deviation for each coordinate component.

For example: Suppose Joe Surveyor has several control stations in his network. Suppose further that for one of these stations he would like to allow movement during the adjustment. He could just set the station to be free, but it may move more than he wants. Alternatively, he can set the station to be constrained in 2D latitude and longitude.

By specifying a known coordinate and standard deviation for both latitude and longitude, Joe Surveyor is applying a constraint on that station. The station will be allowed to move, but will be constrained by these standard deviations. During the adjustment, the coordinate components for this station may move a bit more or less than the governing constraint.

They may not move at all if the known coordinate components for the station are accurate and the survey is of high quality. Most users do not use the constrained option, because they want their control to remain fixed without having to explicitly define small standard deviations for each fixed station component latitude, longitude and height. Some users use the constrained station in order to propagate the statistics standard deviations of the adjusted coordinates from a prior survey in which those stations are now the control in the new survey.

Others would consider those stations adjusted and good, and should be fixed for any subsequent networks tied to them. Please see the FAQ How can I fix the latitude or longitude of a station but not both for the preferred way to constrain a station using a coordinate observation. What is the purpose of the Confidence Level setting? What is the difference between a Confidence Level setting of 0. The confidence level parameter allows the user to set up the Chi Square probability scaler useful for making hypothesis tests as to the quality of the survey.

The least squares process automatically computes all statistical results at the This is why the results generated are in terms of 1 standard deviation. Many of the statistical results generated during the network adjustment give the surveyor an indicator as to the quality of the survey or portions of the survey. For example: The distance error is an indicator as to the quality of the adjusted distance between two stations. If the confidence level were set to Put another way, at the To report this, the 1 sigma results must be scaled to roughly 2 sigma.

Try changing the number to They will become more optimistic lower PPM's and higher ratios. You can also change it without re-adjusting. This can save considerable time when processing with large surveys.

Within the Residual Distribution histogram, what are the units for the Y-axis? What are the meaning of the values 0. The units along the Y axis refer to the relative frequency of occurrence for the standardized residuals.

Two independent network-station constraint approaches are considered: a GPS network fixing a single station was implemented and was followed by a second network solution in which several IGS stations were constrained. The elevation-cutoff angle was set to 0 to obtain the maximum influence of the TD model at altitudes close to the horizon. Results of the final solutions depend more on the constrained stations within the study area than on the type of tropospheric model or antenna type.

Depositar documentos Registrarse. English Contactar. Exportar a otros formatos. Resumen Accurate GPS positioning requires correct modeling of tropospheric refraction, the phenomenon responsible for tropospheric delay TD.