I have seen the HARN acronym but never knew what it was. We will check into
it.
I just re upped our annual subscription to the VRS system...
-----Original Message-----
From: Brian Webster
Sent: Wednesday, May 6, 2020 10:14 AM
To: 'AnimalFarm Microwave Users Group'
Subject: Re: [AFMUG] Elevation question
Does the USGS have any HARN stations in your region? You could use those
instead and they should be free. Might just require you to occupy the point
longer because they might be farther away.
Thank you,
Brian Webster
www.wirelessmapping.com
-----Original Message-----
From: AF [mailto:af-boun...@af.afmug.com] On Behalf Of ch...@wbmfg.com
Sent: Wednesday, May 6, 2020 12:10 PM
To: AnimalFarm Microwave Users Group
Subject: Re: [AFMUG] Elevation question
$600/year here in Utah...
-----Original Message-----
From: Mark Radabaugh
Sent: Wednesday, May 6, 2020 9:57 AM
To: AnimalFarm Microwave Users Group
Subject: Re: [AFMUG] Elevation question
Josh,
In Ohio ODOT has a statewide RTK system set up that you can get free access
too. It’s accessible over the internet so as long as your GPS receiver can
connect to your phone to make the data connection to the state RTK system
you can use the data.
ODOT built if for their own use but make it available to the public to use.
I believe in some locations they will set up a 900Mhz or similar repeater
system to broadcast the data but most of the time they just use cellular
data links.
Mark
On May 6, 2020, at 11:37 AM, Brian Webster <i...@wirelessmapping.com>
wrote:
https://en.wikipedia.org/wiki/Real-time_kinematic
Real-time kinematic (RTK) positioning is a satellite navigation technique
used to enhance the precision of position data derived from
satellite-based positioning systems (global navigation satellite systems,
GNSS) such as GPS, GLONASS, Galileo, NavIC and BeiDou. It uses
measurements of the phase of the signal's carrier wave in addition to the
information content of the signal and relies on a single reference station
or interpolated virtual station to provide real-time corrections,
providing up to centimetre-level accuracy.[1] With reference to GPS in
particular, the system is commonly referred to as carrier-phase
enhancement, or CPGPS.[2] It has applications in land survey, hydrographic
survey, and in unmanned aerial vehicle navigation.
Thank you,
Brian Webster
www.wirelessmapping.com
From: AF [mailto:af-boun...@af.afmug.com] On Behalf Of Brian Webster
Sent: Wednesday, May 6, 2020 11:33 AM
To: 'AnimalFarm Microwave Users Group'
Subject: Re: [AFMUG] Elevation question
High end stuff. I never trust any consumer grade GPS device altitude
readings. I have seen them off by as much as 300 to 400 feet. High end GPS
devices rely on either a real time data link to ground reference stations
or they post process the data back at the office. This is a process where
you time sync your data with the ground reference stations, calculate the
timing difference based on your location distance from the ground control
points. The ground control points have a known coordinate and altitude.
They then compare the GPS readings at their point for those time reference
points you process against. They calculate the correction factor from the
GPS against the known point, then also correct your data based on the
distance/time from the ground station and correct your data. For older GPS
units you sometimes had to occupy a point for a longer period of time
based on your distances from the control points.
High end GPS units can also do RTK or real time kinematic data collection.
This is done by either having a GPS base station controller that is real
time data linked to ground control stations or that the rover unit has the
real time data connectivity. They do all the above processing steps in
real time, no post processing after the field work is done. Depending on
the equipment and setup, there are time requirements to have the
instrument on point to achieve the desired level of precision. Depending
on the type of work, faster systems are desired when you are doing things
like having to stand in traffic to map every manhole and gas valve. Other
uses that are slower can be fine if you can leave it on a tri-pod or
bi-pod for 30 seconds or longer. Slower systems are preferred by workers
getting paid prevailing wages ;-)
Thank you,
Brian Webster
www.wirelessmapping.com
From: AF [mailto:af-boun...@af.afmug.com] On Behalf Of Josh Luthman
Sent: Wednesday, May 6, 2020 11:17 AM
To: AnimalFarm Microwave Users Group
Subject: Re: [AFMUG] Elevation question
local Geoid data set loaded
Is this something most GPS radios would have? Or just higher end ones?
Josh Luthman
Office: 937-552-2340
Direct: 937-552-2343
1100 Wayne St
Suite 1337
Troy, OH 45373
On Wed, May 6, 2020 at 10:36 AM Brian Webster <i...@wirelessmapping.com>
wrote:
OK here is what I learned from my brother.
You want to use the Geoid values, however you also want to make sure you
have the Geoid model loaded in to your Trimble R8 GPS. (for those not
paying attention that is a survey grade instrument with cm accuracy).
The geoid numbers are tied to the map projection you are using and they
are also tied to the GPS ground stations you are connected to 9necessary
for the cm grade accuracy). The Ellipsoid values assume that the earth is
perfectly/mathematically round. Geoid values correct for the fact that it
is not perfectly round and the reason why your GPS needs the local Geoid
data set loaded before you take readings. You do have the Geoid data for
your area loaded don’t you?
For radio mobile you will want to use the Geoid height converted to
meters.
Is there LIDAR data for the area in question? It might be easier just to
use a value from that. Might also be nice to convert the LIDAR to a file
format for Radio Mobile and use all that data (going to need a lot of disk
space though).
Thank you,
Brian Webster
www.wirelessmapping.com
From: AF [mailto:af-boun...@af.afmug.com] On Behalf Of ch...@wbmfg.com
Sent: Tuesday, May 5, 2020 2:12 PM
To: af@af.afmug.com
Subject: [AFMUG] Elevation question
I have a pretty good GPS receiver. Trimble R8 with a Yuma data collector.
Normally we use it only for lats and longs.
It is corrected in real time with a cellular data modem and a RTK/VRS
ground station network.
Yesterday we did a shot from a hill that did not exist when shuttle radar
data was taken. It was way off in elevation.
So we took a shot from our parking lot and compared it with what we think
we know to be the altitude as well as our cell phones and google earth.
Turns out the R8 has an ellipsoid height as well as another height
associated with the northing and easting values.
The second one seems to be more in line with what I was expecting.
The local dealer sent me a drawing showing this. (attached)
So now I am super confused. Not sure what number to use when working with
Radio Mobile. Do I add the geoid height to the ellipsoid height?
Was hoping Brian Webster may know or others may know. Googling google
earth elevation talks about different versions of geoid. Not sure if
their elevations are geoid elevations or not.
So, rather than dig into it any more I am taking the lazy approach and
posting the question here.
--
AF mailing list
AF@af.afmug.com
http://af.afmug.com/mailman/listinfo/af_af.afmug.com
--
AF mailing list
AF@af.afmug.com
http://af.afmug.com/mailman/listinfo/af_af.afmug.com
--
AF mailing list
AF@af.afmug.com
http://af.afmug.com/mailman/listinfo/af_af.afmug.com
--
AF mailing list
AF@af.afmug.com
http://af.afmug.com/mailman/listinfo/af_af.afmug.com
--
AF mailing list
AF@af.afmug.com
http://af.afmug.com/mailman/listinfo/af_af.afmug.com
--
AF mailing list
AF@af.afmug.com
http://af.afmug.com/mailman/listinfo/af_af.afmug.com
