A 4.130Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE
I don’t have any inside knowledge if the US government is going to shut down again this year. But I do know if there is a shutdown like there was in October 2013 I am going to have a hard time grounding surveys without the National Geodetic Survey’s OPUS products. One never knows what the government might do!
While there are several free alternatives to OPUS (see the OPUS alternatives sidebar), unfortunately none return NAD83-2011, NAVD88 orthometric results.
Normally I use the online HTDP and GEOID 2012A tools at the NGS website to transform coordinates but these tools were unavailable during the last shutdown. We certainly cannot count on them during the next shutdown.
Standalone versions of these programs exist, now is the time to download them–before the next catastrophe. If the government does not shut down, you won’t need them. If the government does shut down then, you will be able to operate in a pinch without OPUS.
What To Download
There is complete list of direct links to download at: http://goo.gl/5qptq9. Here is a summary of the tools and data:
HTDP: Transforms between `IGS08 current epoch’ and `NAD83-2011 epoch 2010.’
INTG: You need to report your observed points using orthometric NAVD 88 vertical datum however all of the alternative services report only ellipsoid heights. INTG combined with the latest Geoid12A grid files will allow you to transform a NAD83 framed ellipsoid height to NAVD88.
SPCS83: This tool will convert geographic (Latitude/Longitude) coordinates to State Plane Coordinates.
Datasheets: Each month a single ZIP archive file is updated with a full set of data sheets. If you routinely use data sheets, having a local copy can be a lifesaver.
Using These Tools On A Sample Observation
I won’t lie and tell you that the stand alone tools are as convenient as OPUS. They are DOS tools and data entry is tedious. But they do work, and if you need them you will be glad to have them.
Let’s work through an example by submitting a 2-hour occupation to both AusPOS and OPUS. We can then use HTDP, INTG and SPCS83 to convert the IG08 coordinate from AusPOS to NAD83 and then we can compare the converted coordinates with the OPUS output.
I choose to use a two-hour file from a site just south of the Great Salt Lake that was collected November 5, 2014.
Submitting this file to AUSPOS yields this solution:
See PDF
Next use the HTDP.exe program to transform to NAD83-2011 2010. My responses are highlighted in yellow:
See PDF
Mark Silver is an Electrical Engineer, a topographic map collector, and a longtime vendor of GPS products.
Sidebar:
Some OPUS Alternatives
(direct links provided at http://goo.gl/5qptq9)
AUSPOS: Geoscience Australia
www.ga.gov.au/bin/gps.pl
CSRS-PPP: Canadian Spatial Reference System, Natural Resources Canada
webapp.geod.nrcan.gc.ca/geod/tools-outils/ppp.php
GAPS: University of New Brunswick
gaps.gge.unb.ca/indexv520a.php
magicGNSS: GMV
magicgnss.gmv.com/ppp/
CenterPoint RTX: Trimble Navigation
www.trimblertx.com/UploadForm.aspx
RTX provides NAD83 framed results, but does not return an orthometric height.
The JPL APPS tool is omitted as it has an output issue.
The Scripts Orbit (SOPAC) SCOUT tool is currently unavailable.
A 4.130Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE