EB85A GPS data

[pseddon 1]

I am trying to write an application to monitor the output from an EB85A GPS but am not sure as to the format of the Speed, Altitude and Heading data.

The manual says:

Speed x.xxx knots

Course over ground xx.xxx degrees ref north

Altitude xx.xxx metres above mean sea level

As my GPS is reporting my altitude at 147.4 I am not sure what the manual means and how the data will vary as we go from say 0m to 5000m.

Can anyone help interpret the manual for me and tell me what I can expect for each of these data sets?

regards Peter

[Mr.RC-Cam 121]

Can anyone help interpret the manual for me and tell me what I can expect for each of these data sets?

The data you see is relatively useless if you are statically testing it on the bench. To see good examples of what happens to the data, jump in your car (have someone do the driving), and watch the data as you travel around. As they say, a picture is worth a thousand words.

As my GPS is reporting my altitude at 147.4 I am not sure what the manual means

The altitude is referenced to mean sea level. If you want to reference the reported altitude value to your current ground location then your host needs to subtract the value it measures while still on the ground. This can be automatic at power up (and after satellite lock), or the user could be instructed to press a button to zero the altitude. BTW, your host's code should allow for negative altitude values to be reported.

[ThomasScherrer 0]

the EB85 is known to repport zero speed and/or zero height for 5-10 sec.

in special situations, like flying arround like crasy with rapid changing speed and direction and height

within a relative small area, you need a wild combat wing and skils :-)

but even I can do this.

it will go back to normal opperation if you fly nice for a short while.

[FPVProject 0]

So can I assume that the Course Over Ground reading is useless while stationary ? How do people determine their initial heading when starting ? Are they just moving slightly and calculating bearing from the 2 coordinates ?

Thanks

[Mr.RC-Cam 121]

Course data is not valid until a GPS is traveling. There is a minimum speed that must be maintained (a few kph) to ensure accuracy.

[FPVProject 0]

So what is the best way to determine inital heading using only a GPS ? I am thinking about this in terms of waypoint navigation. Obviously a bearing and distance is better than checking the current coordinate in relation to the given coordinate ( which I imagine would cause a side to side/hammerhead type response).

If you'd prefer me to start a new thread Mr RC.Cam let me know.

[ThomasScherrer 0]

you dont need initian bearing.

we dont use the bearing in the IFOSD we display and repport it.

to calculate home distance, direction, we use first good lock position,

and compare it with actual position and flight direction is calculated using gps positions,

also the slower you move the more jitter in % you will have, that actually apply to several of the gps parameters,

but worst is the heading readout.

[Kilrah 2]

So what is the best way to determine inital heading using only a GPS ?

You don't. You just start in a random direction, which will allow you to get a heading reading, then correct your direction according to it.

[FPVProject 0]

you dont need initian bearing.

we dont use the bearing in the IFOSD we display and repport it.

Can you elaborate Thomas, why don't I need initial bearing/heading at point A if I want to determine bearing from A to B ?

You don't. You just start in a random direction, which will allow you to get a heading reading, then correct your direction according to it.

So far the gps seems to be +- 5m so I assume the 2 positions needed to determine heading would need to be greater than 5m ? What sort of distances have you found to be required Kilrah ?

[Mr.RC-Cam 121]

From what I can recall, none of us here have ever bothered to know the initial heading/course bearing at the moment of launch. Frankly, that requirement is very unusual. However, if it is essential in your application, then you will need to add appropriate compass hardware to your installation. A ready to use tilt-compensated digital compass with a host interface is very expensive (budget $300-500). BTW, some affordable Garmin handheld GPS devices have a digital compass in them (but they are not tilt compensated).

Since your member name is FPVProject, and you are at a hobby site looking for advice, I will assume your application is hobby R/C aerial FPV. In that case, you will be taking off under R/C control and at some point after launch you will require accurate heading data. In a nutshell, it is MUCH simpler to just ignore the heading data at the instant of the launch. Within a second or two the data will be just fine. That's how its usually done.

BTW, if your FPV project involves a ground vehicle then the concept is the same. However, if the vehicle's travel speed is just a couple kph then overall GPS accuracy will be problematic. YMMV.

So far the gps seems to be +- 5m so I assume the 2 positions needed to determine heading would need to be greater than 5m ?

The heading accuracy improves with ground speed. Under 3-4 kph (approx) the data may not be reliable. Once you get past a fast walking speed the heading/course data will be suffciently accurate to satisfy an FPV application. If the GPS stops moving, the heading data will be useless.

The best thing to do is to just setup a simple mobile test and try the GPS module out. You will soon see what it will do under different travel conditions.

Edited March 28, 2008 by Mr.RC-Cam

[Kilrah 2]

I've actually just observed that on my new phone's integrated GPS, in a train the first update after start (~1 second) was already within 5° of the value that would be displayed a few seconds later when the speed had become higher. I'd say as soon as you get to about 5km/h the heading is accurate enough for most uses. As an excample, when walking it also works pretty well.

[FPVProject 0]

Thanks for your detailed response Mr.RC-Cam. Perhaps I should have stated first bearing ? as opposed to first. I have looked at the sparkfun compass modules, but I figured that the easiest and most likely way people people were determining heading was by coordinates (just wanted to check ).

While FPV is certainly the main aim of this project, I am also interested in exploring the other areas that the onboard equipment will allow.

This is something I've wanted to do for years and now I finally have the money to do it. I must say since I first started looking into this type of project it's come a long way. It's great to see that many others are also interested in this field and that there are communities such as this one willing to help one another in doing so.

Eventually I would like to move to aircraft but initially this will devoloped on an RC Buggy.

Don'y worry there will be plenty of driving to come

Thank you for your advice so far (an expect many more questions to come )