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The Albuquerque area geoidal model has been developed to aid users of the ARTGN, or any other RTK GPS systems, in the establishment of orthometric heights from GPS observations.
We currently have the model available in three formats: Generic NGS, Topcon and Trimble proprietary formats. These may be downloaded throught the links below:
GCOA2008.zip (NGS Binary .bin file type)
ABQJUL08.zip (Topcon proprietary .gff file type)
COAJUL08.zip (Trimble proprietary .ggf file type)
NOTE: Files are only zipped to make the download process work through the webpage.
The contour map shown below of the N values was developed to show the spatial extent of the model and the shape of the geoidal undulations. There is a 1.7 meter difference in the contour values from the upper right of the map to the lower left. For a closer look at the map view and/or save the pdf version from the link below and zoom into the area of interest:
The geoidal separation values (N values) were developed by differencing orthometric heights from ellipsoidal heights on six hundred Albuquerque Geodetic Reference System (AGRS) data points spread throughout the metropolitan area of the City. The names and geospatial distribution of these points can be seen by zooming into the pdf version of the map. These points had both high accuracy ellipsoidal heights derived from static gps observations as well as orthometric heights derived from many years of geodetic leveling operations. A TIN was generated from these differences. A grid of 65,000 points at three second intervals of latitude and longitude was developed and dropped down vertically over the TIN. Geoidal separation values were generated where the vertical lines from the 65,000 nodal points intersected the facets of the TIN. These 65,000 points were used as input into the geoidal model. The 65,000 N values were converted into binary files for import into user software.
PLEASE CAREFULLY NOTE the spatial extent of the model. Geoidal separation values computed along the edges and off the edges of the extents of the contour lines will be erroneous. Users will need to switch to a portion of the NGS nationwide model in areas along the edges area of the contour lines or in the area outside the contour lines.