For GPS/GNSS tech-weenies only

You were warned in the title of this thread. If you're not a GPS/GNSS tech-weenie, what are you doing here still?

The BBC has published an article about the launch of a new European "GNSS" satellite with a new hydrogen maser atomic clock on board. EDIT: DOH! Here's the forgotten link: Atomic rhythms give precise fix. (For you non-GPS/GNSS tech-weenies who are still with us, "GNSS" is Euro-speak for "GPS," used to show their independence from you-know-whom.) The clock will facilitate one-meter precision, instead of the several-meter precision that we generally see in outdoor handheld receivers.

In addition to the news about the clock, the article provides a pretty good description of how a GPS -- oops, "GNSS" -- receiver works. (Except it leaves out the role of a datum. You can learn about datums at the Map Datums article on MapTools.com.)

sardog1 said:

The BBC has published an article about the launch of a new European "GNSS" satellite with a new hydrogen maser atomic clock on board. (For you non-GPS/GNSS tech-weenies who are still with us, "GNSS" is Euro-speak for "GPS," used to show their independence from you-know-whom.) The clock will facilitate one-meter precision, instead of the several-meter precision that we generally see in outdoor handheld receivers.

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BBC link?

GNSS=Global Navigation Satellite System
GPS=USA GNSS. Currently operational.
Galileo=European GNSS. Has had political and funding problems. Now projected to be operational ~2013.
Glonass=Russian GNSS. Currently has insufficient satellites in orbit.
(There are more in the works.)

http://www.ngs.noaa.gov/CORS/Newsletter/042308.pdf
http://en.wikipedia.org/wiki/Satellite_navigation_system

The European Galileo system has often been misleadingly advertised. Its PR compares its projected future performance with the current performance of GPS. By the time Galileo is actually operational, the performance of GPS will have improved and the performances are expected to be similar. The two systems have been designed to be inter-operable so the satellites can be used together.

In addition to the news about the clock, the article provides a pretty good description of how a GPS -- oops, "GNSS" -- receiver works. (Except it leaves out the role of a datum. You can learn about datums at the Map Datums article on MapTools.com.)

Click to expand...

Actually, the datum is a minor issue for the GPS. Much of the internal computation is done in ECEF (Earth-Centered, Earth-Fixed) coordinates. The final results are then converted to a datum for user display.

Also the current error budget (http://www.edu-observatory.org/gps/gps_accuracy.html, Table 2) shows the ionosphere, not the satellite clock to the the largest source of error. In the future, dual frequency (civilian) operation will enable to GPSR to reduce the ionospheric error (Table 4). (Higher accuracy is currently obtained by DGPS (Differential GPS) or post-processing with measured rather than predicted satellite info. Survey grade accuracy also adds carrier phase processing.)

There is also a tutorial at http://www.gpsinformation.org/dale/theory.htm,
and a list of tutorials at http://www.edu-observatory.org/gps/tutorials.html

Doug

Talk about weenies -- posts a new thread and leaves out the link to the mentioned article. (See the fix above.)

(Actually, the datum is an issue for folks who aren't aware of its importance in matching GPS receiver and map, or matching GPS receiver and a list of waypoints. I threw in the link to alert the uninitiated to this. When I have completed my master plan to convert the U.S. to UTM from lat/lon, it will be a bigger deal.)

DougPaul said:

The European Galileo system has often been misleadingly advertised. Its PR compares its projected future performance with the current performance of GPS. By the time Galileo is actually operational ...

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Given its profound political (read: funding) problems I wonder whether "... assuming it becomes operational ..." might be more accurate

DougPaul said:

In the future, dual frequency (civilian) operation will enable to GPSR to reduce the ionospheric error (Table 4). (Higher accuracy is currently obtained by DGPS (Differential GPS) or post-processing with measured rather than predicted satellite info.

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NOAA is working on providing post-processing to help reduce the ionospheric error as well. Those satellites have been an absolute boon to ionospheric research.

Mohamed Ellozy said:

Given its profound political (read: funding) problems I wonder whether "... assuming it becomes operational ..." might be more accurate

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Originally the idea was to use commercial money which would be paid back by charging users. Pretty hard to do with equivalent service available free from the USA.

After failure to achieve agreements and slipped deadlines, they have switched to EU/government funding.

We shall see what happens...

Doug

jniehof said:

NOAA is working on providing post-processing to help reduce the ionospheric error as well. Those satellites have been an absolute boon to ionospheric research.

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DGPS reduces the errors due to unknown ionospheric delay because it uses a local reference GPS to obtain reference values for the signal arrival times. The errors in these values are very similar for two close GPSes. (WAAS is a coarse form of DGPS.)

Dual frequency operation allows the GPSR to measure the ionospheric delay because it is different at each frequency in a predictable way.

Current GPSes use a model to estimate the ionospheric delay, but are unable to measure it.


Agreed: by operating a GPS at a known location and using the changes in the signal have been very useful for atmospheric/ionospheric research. Kind of an inversion of the more common satellite-borne sensors--the signals come from the satellites and are measured on the ground.

Doug

Some of us pseudo-geeks can almost understand some of this stuff

To the GPS wizards and weenies

Is there a way to convert from GPS to GIS?

Using ArcGIS I put the GPS data into Excel, save as a .dbf and open the dbf shapefile with ArcGIS

Yes. If you have access to a GIS and you're running Windoze, your best bet is DNRGarmin, freeware from the Minnesota Department of Natural Resources. If you're on a Mac, GPSBabel and LoadMyTracks are good shareware; MacGPS Pro is better but costs a little money.

Yes, in general you can import GPS data into a GIS.

I've never used one so I have no recommendations. Info on free GIS may be found at http://www.freegis.org/.

For those not up on their acronyms:
GIS=geographic information system
General info at http://en.wikipedia.org/wiki/Geographic_information_system

Doug

Puck said:

To the GPS wizards and weenies

Is there a way to convert from GPS to GIS?

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by GIS do you mean a shapefile? if so then what the others said. I use ExpertGPS (http://www.topografix.com) with the GIS option pack, it's not free but a lot easier to use than DNRGarmin or GPSBabel. For GIS viewers I use TatukGIS (http://www.tatukgis.com), but that's fairly rare -- most of the time ExpertGPS does what I want.

Thanks for the responses. I have not had time to dive into them.
My situation, I was given GIS coordinates and need to convert to GPS.
It is for a bird survey on Ammonusuc Ravine Trail. Once I get the locations I will confirm with my GPS

This is what I have;
1. 44.26606 x -71.32457
2. 44.26724 x -71.32644
3. 44.26724 x -71.32875
4. 44.26682 x -71.33127
5. 44.26655 x -71.33371

Puck said:

This is what I have;
1. 44.26606 x -71.32457
2. 44.26724 x -71.32644
3. 44.26724 x -71.32875
4. 44.26682 x -71.33127
5. 44.26655 x -71.33371

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Oh -- that looks like just latitude & longitude. The first column is latitude (decimal degrees N) & the second is longitude ("-" sign means decimal degrees W)

Puck said:

Thanks for the responses. I have not had time to dive into them.
My situation, I was given GIS coordinates and need to convert to GPS.
It is for a bird survey on Ammonusuc Ravine Trail. Once I get the locations I will confirm with my GPS

This is what I have;
1. 44.26606 x -71.32457
2. 44.26724 x -71.32644
3. 44.26724 x -71.32875
4. 44.26682 x -71.33127
5. 44.26655 x -71.33371

Click to expand...

Those are just lat and lon for some points.

GPSBabel can convert them into waypoints in a GPS-software (eg .gpx) file format. If you know .gpx file format, you can also just hand edit them into the file. (Produce a .gpx file from your software and take a look--it is a text-based xml format.)

If you only have 5 points, you can easily enter them through Mapsourse if you have a Garmin GPS or enter them on the front panel of the GPS itself.

Doug

I m not well versed in this area. The points did look like they had the lat and long in degrees but the rest of the digits were not min and sec.

I have the Garmin Mapsource software so I will see what I can do. Thanks for the help.

Puck said:

I m not well versed in this area. The points did look like they had the lat and long in degrees but the rest of the digits were not min and sec.

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Lat and lon are commonly represented in any of 3 formats:
ddd.ddddd (used here)
ddd mm.mm
ddd mm ss.ss

(In all cases, the number of digits to the right of the decimal point can vary.)

Make sure you match datums. (GPS native is WGS-84 and .gpx files are WGS-84).

Doug

As long as we are somewhere near this topic: a new release of GPSBabel just came out (v1.3.5). http://www.gpsbabel.org

Doug

Puck said:

Thanks for the responses. I have not had time to dive into them.
My situation, I was given GIS coordinates and need to convert to GPS.
It is for a bird survey on Ammonusuc Ravine Trail. Once I get the locations I will confirm with my GPS

This is what I have;
1. 44.26606 x -71.32457
2. 44.26724 x -71.32644
3. 44.26724 x -71.32875
4. 44.26682 x -71.33127
5. 44.26655 x -71.33371

Click to expand...

Ahh, the answer you got from me had nothing to do with your actual need.

Your question appears to ask, "How can I convert this list of five locations, currently expressed in latitude and longitude, into something I can use in my GPS receiver?" The simplest solution, given the very short list you have, is to put them into your GPS receiver one at a time, as new "waypoints" (Garminese for individual locations identified by coordinates.") Any handheld GPS receiver is capable of doing this. Look in the manual for "Mark Waypoint" and/or "Create Waypoint" or the analogous term for your brand of GPS. Be sure that you know the datum used to create the list and use the same datum in your GPS receiver before you start entering the lat/lon coordinates. (This becomes a much bigger deal if your question is actually the next one.)

If your question actually asks, "How do I convert this list of lat/lon coordinates into UTM coordinates?" -- that's easy. Again, be sure that you first set the datum on the GPS receiver to match the datum used for the original list. Then enter all locations with their respective lat/lon coordinates. Then change the "position format" to UTM (aka UTM/UPS, aka Universal Transverse Mercator.) Be very, very sure that you don't enter the coordinates first and then change the datum.

("GIS" is "geographic information system," which is a way of relating spatially-referenced data in layers on a map. In the old days, your teacher (well, mine at least) pulled down acetate layers on wall-mounted maps to show how rivers and towns were related to each other spatially. These days, it's done on a computer -- with the capacity to show you where bald eagles nest in Maine, or what your neighbor paid for his house and how big his master bedroom is. "GPS" is "global positioning system," a way of locating places accurately and precisely using orbiting satellites and a specialized computer/radio receiver/clock known as a GPS receiver. GPS data can be used in a GIS. And data created in a GIS can be transferred into a GPS receiver to take into the field.)