N E T V A L

Description

NETVAL is a software package that provides analysis tools for evaluating GPS surveys. It is well known that traditional methods of assessing the accuracy of networks using 95% confidence regions are too unreliable for GPS. Consequently many government agencies are now developing specifications for GPS surveys following the approach advocated by Craymer, Vanicek and Wells in their "Report on Urban GPS Research Project, Phase III Ð Evaluation, Volume 3, Specifications and Guidelines" prepared for the City of Edmonton. By this approach potential contractors are required to demonstrate their ability to perform GPS surveys to a specified accuracy on a test network. NETVAL can be used to evaluate such results and to determine whether or not the required accuracy has been achieved.

NETVAL is primarily designed for use by agencies responsible for contracting out GPS surveys. NETVAL will permit these agencies to check whether a potential contractor's GPS results meet a specified accuracy. Presently the Province of Alberta and the Canadian Geodetic Survey both use NETVAL to evaluate potential GPS contractors on their test networks. In addition to validating potential GPS contractors, NETVAL can also provide a check on the accuracy of densification networks by comparing computed positions at control points with their known values.

Potential contractors can also benefit from NETVAL by checking that their procedures for GPS surveys are capable of satisfying the accuracies required by contracting agencies. This can be done prior to any validation testing by the contracting agency thereby avoiding embarrassing failures.

NETVAL evaluates both the internal and external accuracy of a 3-dimensional network using a variety of network analysis tools. The internal accuracy is based on the covariance matrix of the GPS network which is known not to be very reliable. The external accuracy analyses provides a more reliable method to assess the quality of the results by comparing them to known values established by higher order standards.

NETVAL consists of the following suite of 6 programs:

NETDAT

Converts GeoLab data files to the format required for input to the following NETVAL programs.

NETREG

Evaluates the internal accuracy of a network by computing 1-d, 2-d and 3-d absolute and relative confidence regions at a specified confidence level for all stations and station pairs. The sizes of the regions are checked against the maxima allowed by 1st, 2nd or 3rd order specifications.

NETDIF

Evaluates the external accuracy by analysing the coordinate differences between the test results and the known positions. The differences are checked against the maxima allowed by 1st, 2nd or 3rd order specifications and a variety of statistical tests are used to check the compatibility of the test results with the known positions.

NETRAN

Evaluates the external accuracy by computing datum differences such as translations, rotations and scale differences between the test results and known positions. The test network may optionally be corrected for any such datum differences for further analyses.

NETSTR

Evaluates the external accuracy by computing local distortions of the test results with respect to the known positions. The distortions are given in terms of strain parameters at each point.

PLTSTR

Graphically displays and prints the strain parameters determined by NETSTR for easy identification of distorted areas of the network. NO LONGER DISTRIBUTED DUE TO INCOMPATIBILITY WITH MODERN PC'S.

Download

netval16.zip (403 KB)

System Requirements

Documentation & Support

NETVAL_Ref.pdf (141 KB)

NETVAL is presently being distributed free of charge but without any support. Use at your own risk.