DMEX97
DMEX97 is a companion product derived from
MEXICO97.
The geoid is a
surface of constant potential which conforms to sea level in an average
sense. Deflections of the vertical are the slopes associated with the
Earth's equipotential layers. The deflection of the vertical is the
departure a plumb bob would take from vertical defined by an ideal
ellipsoidal Earth. These quantities are typically a few arc seconds,
but can reach an arc minute of departure.
Deflections are used to relate the orientation of a locally-leveled
instrument, such as a theodolite, to a spatial reference system.
Important uses are corrections to zenith distance (vertical angle)
measurements, and the conversion between astronomic and ellipsoidal
azimuths (the Laplace correction).
The DMEX97 model is a high resolution deflection of the vertical model
covering the region 14-33N, 119-86W. It has been prepared in cooperation
with the Instituto Nacional de Estadistica, Geografia e Informatica
( INEGI).
The DMEX97 deflection model has been designed specifically for
Mexico. Due to data coverage and computational issues, one will find
differences between DMEX97 and DEFLEC96 in regions of overlap.
The below image (and others on this page) represent the computational
area of DMEX97, not the released area.
PC Software
Full Size Image, DMEX97 Model (e/w component)
Images of Terrain, Gravity, Geoid, and Deflections
Geoid, Gravity, Deflection, and Data Coverage Grids
Frequently Asked Questions
On-Line Papers
The Geoid Research Page
Got a question?
RETURN to the NGS Home Page.
