GPS Navigation Software

[Jlawsen]

I've tried just about all the freebie GPS nav apps out there for a Windows platform and some of them are pretty good but none of them are sophisticated enough to allow any type of modeling. The Navionics stuff doesn't allow for the use of GPS reciever input nor does Map Create 7 (LEI). Google Earth will take input from my GlobalSat antenna via NEMA 183 and it's o.k. but there's no current contours for lakes.

My goal is to find a software product that will adjust the depths and shore line based on current elevations vs. when the last available Hydrologic data was derived.

USGS has several modeling pieces that will work but as is typical the number of pieces is organized in a manner that makes it impossible to find the right piece without trying them all. That takes a lot of time and I only have 3 pcs at my desk right now to do comparisons with.

If all else fails I'll just write the software myself but I thought maybe someone here might know of a off the shelf product that would work for me.

If you havent already figured it out what I'm try to do is predict the depths of fixed underwater hazards and then display it visually so you can see that rock pile that is 6' under in the spring and exposed in the late fall.

 

[tx1961whaler]

Re: GPS Navigation Software

Don't know if this is what you want, but it does have depth offset capability
http://www.humminbird.com/leading_innovation/cartography-gps-maps.aspx

 

[JB]

Re: GPS Navigation Software

Hmmmmm. Maybe you are overthinking this problem.

Most depth reading charts give a depth below some arbitrary water surface level (when the readings were taken). Most GPS receivers are capable of displaying elevation (above sea level) for a given waypoint or fix, including the surface of the water you are on. Seems to me that it would be a simple matter to relabel the charts giving elevation above (or below) sea level of bottom features. Your PC could then ask the GPS what the current elevation of the water surface is and display bottom feature depth below that real-time elevation reading.

Is that what you are after? A lot of very basic arithmetic for your 'puter, but a given chart could be converted in a few milliseconds.

 

[Jlawsen]

Re: GPS Navigation Software

JB & TX I have the navionics platnum and I can do the math and figure out how deep the lake is now. What I want to do is create a 3d model that uses the current water level elevation and then uses the current USGS data to show the new shoreline and depths.

In reality I want a lazy man's up to the minute 3D map that will show a hazard warning for any new fixed underwater hazards that have occured due to lake level changes. The Fathometer/GPS elevation method works great to gather real time hydrographic data and I will be doing a lot of that during my 2 month fishing trip that starts next week.

So here's the scenario - Day 1, Boats at the dock: Get current elevation samples from at least 3 GPS units from different manufacturer. My sources are Lowrance HDS 8 Head unit built in GPS, Lowrance 4000 GPS Reciever, Global Sat ND100S USB GPS receiver. Do the math for the corrections from top of the receiver to the water. Do the math and get the average elevation from all three. Take the survey elevation from the nearest monument and subtract it from my corrected elevation to get the difference between the USGS topo map elevations at the time they were created (1992).

Go fishing and run Sonar in the record mode.

Get back to cabin with two nice 3-4lb trout, clean the fish, have lunch, run the sonar log viewer and extract the data. (priorties are important here).

Now I can use all that data to correct the depths, mark the new shorline, update the new hazards, etc.

The point is that this is all data that can be collected in real time. Since that is true and it's pretty much basic math. Any computer can do it with the right software. Taking it a step further to 3D rastor graphic rendering would not be extremely difficult since the coordinate mapping is also present in the GPS sentence. The fixes from the birds are still only accurate to 15 meters with a single gps so you have to take larger samples and from multiple sources to get an average that is accurate enough to navigate in tight situations. With the three receivers and a 2 minute sample I can get within 1 meter. If I had 3 LS-4000 (5 samples a sec) I could do it in about 5 seconds when stationary. That's a long time when your trying to keep a boat away from submerged objects like when navigating a narrow channel.

Would it not be sweet to take the data the you already have, plug it in, let the GPS receiver and fathometer do their thing and when finished, produce a reasonably accurate and up to date map.

I know, no matter how well it works, there's still no substitute for common sense and sharp eyes. I won't loose sight of that.

Thanks for the repsonses.

 

[dolluper]

Re: GPS Navigation Software

USB depth finder.....to printer

 

[bruceb58]

Re: GPS Navigation Software

Most GPS receivers are capable of displaying elevation (above sea level) for a given waypoint or fix, including the surface of the water you are on.

Problem is that GPS is very innacurate in the vertical direction. Could be over 60 feet off.

 

[JB]

Re: GPS Navigation Software

Problem is that GPS is very innacurate in the vertical direction. Could be over 60 feet off.

All GPS fixes are three dimensional, Bruce. Inaccuracies are pretty much the same in all directions. The more satellites contributing to the fix, and the presence of a WAAS corrector signal, the more consistent the fix.

I monitor elevation with my Garmin 276C when traveling and the elevation readings seem more consistent than the lat-lon. I don't remember the actual figures, but when crossing the continental divide in CO several years back, the GPS agreed with the sign by the road within 3 feet.

 

[bruceb58]

Re: GPS Navigation Software

All GPS fixes are three dimensional, Bruce. Inaccuracies are pretty much the same in all directions. The more satellites contributing to the fix, and the presence of a WAAS corrector signal, the more consistent the fix.

They aren't.
http://weather.gladstonefamily.net/gps_elevation.html

General rule is that vertical accuracy is 3 times what horizontal is do to the geometry of the angle of the GPS satellites.

Just do a google search on it. It is explained very clearly.

Check out the manual on your GPS. It will usually state what the difference in accuracy is. WAAS will make it better but it will still be worse than horizontal. WAAS can get the accuracy down to a couple feet in horizontal but it will still be around 10 feet vertical.

 

[Jlawsen]

Re: GPS Navigation Software

WAAS enabled GPS recievers can provide 1-1.5m accuracy. That's what the Gov tested it at but ... You need a aircraft quality GPS reciever to achieve that. WAAS was developed to support the aviation industry which is now using GPS/WAAS for navigation and even precision auto pilot landings. The more channels that you receiver is capable of receiving the better the fix will be. When you combine the GPS/WAAS enabled recievers output with that of a calibrated fathometer you altitude accuracy can be within a few inches. You can further refine the altitude to within 1 or 2 inches if you calibrate your GPS software using the known distance to the center of the earth. The North America location is in Quebec.

This is not the final verdict by any means but I've contacted the Fugawi Software development team and they are going to stage the software developers kit (SDK) on the FTP server for me on Monday. Delorme balked at the idea but Fugawi welcomed it. My C++ skills are a little rusty but it won't take me long to get back up to speed.

I ran a test yesterday while in the driveway and it became obvious that my setup was indequate. The theory was good but the equipment variations were far enough off that it had my boat on top of the neighbors garage at one point. At that rate it would have taken hours to gather enough data to produce the accuracy level that I want to get to.

I just ordered a NEMA 2000 to PC adapter and three Garmin 18x PC GPS/WAAS recievers. That should give me everything from my Lowrance NEMA 2000 Network including the structure scan sounder plus the three Garmins. I can even strip off the SmartCraft data if I want to. If I wanted to spend a big chunk of money on this pet project I'd opt for aviation grade systems and I may end up going that route. The decision I would need to make in order to convince myself to spend that kind of money would be if the end result is a marketable product or not. That's currently not in my plans but not totally shelved either.

Once I get it all configured and working the first goal will be to get the averaged correction factors and do it in a timely manner. When I have those tested and am confident in their accuracy, the system should run on a single GPS/WAAS reciever with Fathometer (Fish Finder Sonar) input.

 

[JB]

Re: GPS Navigation Software

They aren't.
http://weather.gladstonefamily.net/gps_elevation.html

Pseudo scientific gobblydegook, Bruce. What that really explains is that sea level is not always where the math expects it to be, because the earth is not a perfect sphere. In terms of distance to the center of the earth the GPS is more accurate than the maps.

I agree that the phenomenon does introduce apparent errors in elevation vs sea level at certain locations, but not in elevation vs earth center. Those errors are in the charts because sea level varies in distance from earth center.

If we were more interested in true location, in 3 dimensions, we would reference the position to earth center, not earth surface. We are, however interested in earth surface for ground based and low altitude travel. Any fix, however, must be within the GPS sphere, which is limited to an average of about 1200 miles above the surface of the earth.

 

[Jlawsen]

Re: GPS Navigation Software

Here's a link to wikipedia

http://en.wikipedia.org/wiki/Apogee

When it comes to altitude, this is the problem with inexpensive GPS recievers and inadequate software. I called a friend of mine that i used to work with at Naval Satellite Operations Center in Pt. Mugu, Ca. He's sending me the correction data that they use for the commercial aviation industries systems. The timing is in the GPS sentence so that's not a problem. If you know where the bird is at a specific point in time and apply the correction accordingly then the vertical portion becomes easier to stabilize. If you can stabilize it in a reasonable amount of time then it becomes usable. My LMS4000 stabilizes in about an hour if I don't move the boat. On a cold start it runs from 185 up to 210 and then repeats it but each time its slower until it starts knocking a foot off of each end and finally ends up at 195' which is correct according to corrected elevation off the monument in the street.

 

[bruceb58]

Re: GPS Navigation Software

Pseudo scientific gobblydegook, Bruce.

JB, it just a geometry issue coupled with the inaccuracies of the GPS system.

Figured you would understand this concept but apparently I was mistaken.

Maybe you should check out the technical bulletin from the gps.gov site:
http://www.gps.gov/technical/ps/2008-SPS-performance-standard.pdf
It talks about the accuracies between horizontal and vertical. Its a pretty heavy read so you may not understand all the gobblydegook.

 

[Jlawsen]

Re: GPS Navigation Software

JB, it just a geometry issue coupled with the inaccuracies of the GPS system.

Figured you would understand this concept but apparently I was mistaken.

Maybe you should check out the technical bulletin from the gps.gov site:
http://www.gps.gov/technical/ps/2008-SPS-performance-standard.pdf
It talks about the accuracies between horizontal and vertical. Its a pretty heavy read so you may not understand all the gobblydegook.

Bruceb58, WAAS brings us to 1 meter horizontally and 1.5 meters vertically. The reasons there is a 1.5 meter vertical error are many. But since none of the reasons for error are constants the key is in the sample rate. You wil at some point be high and at some point be low. The average between the two over time will eventually give you the correct elevation. How long that takes is the problem. WAAS is considered adequate for an aircraft to land on autopilot without ILS. My quest is to be able to accurately show fixed submerged hazards such as rock piles, etc when a lakes elevation changes. If I turn on my GPS/WAAS reciever and let it gather data for an hour I have proven that I can get a very accurate vertical, far better than 1.5 meters.

In most cases the lakes that I want to map will not have a major elevation change while I'm navigating them. My system would not work if the lakes were effected by tidal changes and may be somewhat inacurate during periods of high winds when water gets moved from one end of a lake to the other. The later can often take more than a day to correct itself.

If you want to continue to argue this that's fine. I can see that my input is no longer desired here so I'll abandon this post and go elsewhere.

 

[bruceb58]

Re: GPS Navigation Software

OK..so assuming you have 1.5M error which is close to 5 feet. So your error when you are recording your data can be +5 feet one day and -5 feet another day for a delta of 10 feet from one day to another. Isn't a 10 foot delta going to be an issue?

My understanding is that commercial aircraft are not using GPS to autoland planes. If you have a link that shows this is not true I would be interested in seeing it. They are using it for approaches only.

 

[JB]

Re: GPS Navigation Software

I don't really disagree with the explanations, Bruce; I just disagree with couching them in such complicated terminology. I do agree with the warning screen that says don't use this for navigation. The warnings sound like the long list of why you shouldn't use this drug we are advertising.

Yes, geometry. No matter how many satellites are involved, all are above a horizontal plane. You could write an unintelligible book with 13 letter words to explain that, but not make it any simpler.

 

[Jlawsen]

Re: GPS Navigation Software

OK..so assuming you have 1.5M error which is close to 5 feet. So your error when you are recording your data can be +5 feet one day and -5 feet another day for a delta of 10 feet from one day to another. Isn't a 10 foot delta going to be an issue?

My understanding is that commercial aircraft are not using GPS to autoland planes. If you have a link that shows this is not true I would be interested in seeing it. They are using it for approaches only.

Actually they are but they do not use GPS alone to accomplish it. The biggest problem that they needed to overcome was how to provide the corrections rapidly enough. The what if scenarious (risk management) showed that there was no way you could use it to auto land a plane because of the multitude of split second corrections that may be needed. However, the scenario changes when you add in laser guidance which is now augmenting GPS assited auto pilot landings. GPS sort of becomes a buzz word at that point.

In the scenario I am attempting to accomplish, the critical element is elevation and without laser refrences to known fixed elevations it may in fact be impossible to get close to perfection. However, the more data you can average the more accurate you become. My current estimate is about 15 minutes of data if I have at least two WAAS birds available. This would establish an elevation that is near enough to real time to re-draw a map and mark obvious and potential hazards. There will be times when the map shows exposed rocks and they are actually beneath the surface but the hazard will exist nonetheless.

 

[bruceb58]

Re: GPS Navigation Software

You don't understand how WAAS works if you think mutiple WAAS sattelites help you. The WAAS sattelite purpose is to send corrections due to Ionospheric errors and GPS sattellite positon errors. They get their info from ground stations and each WAAS sattelite is transmitting the same error correction signal.

So how far are you from one of the ground correction stations?

 

[JB]

Re: GPS Navigation Software

We have also overlooked the fact that "up to 1.5M error" can be anything from ZERO error to 1.5M, meaning that most of the time the error will be less, sometimes a lot less, than 1.5M. This would account for my own real world observations seeming to be a lot more accurate (or at least repeatable) than the worst case scenario all the geometric and atmospheric gymnastics suggest.

 

[bruceb58]

Re: GPS Navigation Software

Here is an interesting test one guy ran:
http://www.doylesdartden.com/gis/gpstest.htm

http://home.comcast.net/~dmilbert/handacc/accur3.htm
Look like he was seeing 11 feet vertical error with WAAS.

http://www.nstb.tc.faa.gov/reports/PAN77_0412.pdf
Go to page 21 for WAAS enabled GPS error for the last quarter.

 

[Jlawsen]

Re: GPS Navigation Software

You don't understand how WAAS works if you think mutiple WAAS sattelites help you. The WAAS sattelite purpose is to send corrections due to Ionospheric errors and GPS sattellite positon errors. They get their info from ground stations and each WAAS sattelite is transmitting the same error correction signal.

So how far are you from one of the ground correction stations?

WAAS is often thought of as a ground reference and I've actually seen info on the internet that would lead one to believe that the ground stations gather all the information and transmit if via HF and I saw one report that said that they were at all major airports and if you were near enough to an airport you could use it.

In reality the ground stations gather specific geographically local information and also get data from other birds such as the ionosphere montioring birds that my former employer (NAVSOC) manages. The WAAS data is protected and transmitted directly to the WAAS birds who then offer that information back to WAAS capable GPS receivers where it is applied. You cannot get data directly from a WAAS ground station.