The California Surveyor - CLSA
The California Surveyor - CLSA
The California Surveyor - CLSA
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HPGN Relation to State<br />
Plane Coordinates<br />
All points within the HPGN will be<br />
recognized as a basis for SPC as<br />
defined in the Public Resources Code<br />
dealing with the <strong>California</strong> State<br />
Plane Coordinate system. <strong>The</strong> latitude<br />
and longitude positions of all<br />
HPGN points will have NAD83 state<br />
plane coordinate values assigned<br />
to them.<br />
HPGN Positional Accuracy<br />
<strong>The</strong> National Geodetic Survey's geometric<br />
relative positioning accuracy<br />
standards for three-dimensional surveys<br />
using space system techniques<br />
are broken down into four levels or<br />
categories of order as follows:<br />
• Order A 3mm+l: 100,000,000.<br />
Used for global & regional geodynamics<br />
(i.e., plate tectonics movements)<br />
and deformation measurements<br />
(i.e, seismic movement).<br />
• Order AA 5mm+l:l0,000,000.<br />
Used for NGRS "primary" networks;<br />
regional & local geodynamics; seismic<br />
measurements.<br />
• Order B 8mm+1:1,000,000. Used<br />
for "secondary" networks; connections<br />
between the "primary" NGRS<br />
network; local geodynamics; seismic<br />
measurements; high precision engineering<br />
surveys.<br />
•Order C<br />
1st 1cm + 1:100,000<br />
2nd-I 2cm + 1: 50,000<br />
2nd-II 3cm + 1: 20,000<br />
3rd 5cm + 1: 10,000<br />
Used for meeting mapping;<br />
land information; engineering<br />
requirements.<br />
Figure 1<br />
<strong>California</strong> HPGN Station Placement<br />
<strong>The</strong> <strong>California</strong> HPGN project was<br />
designed to produce a level of accuracy<br />
of at least Order B as defined<br />
by the FGCS (Federal Geodetic Control<br />
Subcommittee) specifications.<br />
FGCS Order B specifications stipulate<br />
that the vector components of<br />
each station within the network shall<br />
have a minimum accuracy of 8mm +<br />
1:1,000,000 at the 95% confidence<br />
level. For example, at 40 mile spacing<br />
(about 60 km) the expected accuracy<br />
is 8mm + 60mm = 68mm (0.22<br />
feet) for each of the components of<br />
the resultant vectors. <strong>The</strong> procecedures<br />
used to establish the <strong>California</strong><br />
HPGN, however, were intended<br />
to guarantee accuracies as close to<br />
Order A as defined by the FGCS as<br />
was practical. In other words, stations<br />
within the <strong>California</strong> HPGN will<br />
have coordinate values assigned to<br />
them which will be at least 10 times<br />
more precise than those currently<br />
assigned to existing 1st order NGRS<br />
network stations.<br />
HPGN Stations Relation<br />
to NGS Triangulation<br />
Stations<br />
Satellite data was collected on at least<br />
one NGS horizontal control station<br />
(usually 1st order but occasionally<br />
2nd order) within a one degree by<br />
one degree area throughout the entire<br />
length of the state simultaneously<br />
with data being collected on surrounding<br />
HPGN stations. This was<br />
enough to tie the existing NGRS<br />
reference network into the HPGN.<br />
Those NGS points that were occupied<br />
concurrently with the HPGN<br />
points will be assigned revised<br />
N AD83 coordinate values at the same<br />
time the NAD83 coordinate values<br />
for the newly established HPGN<br />
points are published (the middle of<br />
May 1992). <strong>The</strong> ties that were made<br />
between the existing NGRS reference<br />
network and the newly established<br />
HPGN will enable NGS to determine<br />
the amount of adjustment (if any)<br />
that will be necessary to the remaining<br />
16,000 or so 1st, 2nd, and 3rd<br />
order stations within this network.<br />
A least squares adjustment will be<br />
performed at a later and as yet unspecified<br />
date which will be used to<br />
Fall 1992 <strong>The</strong> <strong>California</strong> <strong>Surveyor</strong> 11