Topic: Bathymetric surveys and recording NMEA

[sonarMick]

Hi, this is my first post here.

I’m an aquatic ecologist on the east coast of Australia and a keen fisho. I’ve recently acquired an 899cxi SI with the intention of habitat mapping. I’ve only had the sounder wet once so far, but it promises great things on the SI front.

But on a slightly different tack… we have some background also in hydrographic survey and with the addition of survey grade RTK GPS, which we have access to, I’d like to put together a system to combine the accurate GPS xyz NMEA stream with the ‘bird soundings to give reasonable bathymetric maps.

My first of probably many questions is…

If the GPS nmea is fed into the 899, is it possible for that accurate lat/long and GPS altitude information as well as the Sonar depth to be recorded on the SD card?

Thanks
-   Mick

[sonar2000]

Yes, the information is in the hb sentence structure for depth and lon/lat. Which is all you need for a bathymap. Several companies have programs for creating the maps. check out the site. Si generally does is not used for the maps only the depth and position.
Chuck

[sonarMick]

Thanks Chuck, I've been trawling through the site for info. I haven't got an external GPS hooked up at the moment, but I'm surprised to see that the unit has acquired a reasonable fix despite being well indoors. I notice in the GPS Diagnostic view that 'Altitude' is displayed. I've turned on NMEA output, but I can't see anywhere where the data stream can be viewed. Is it possible to see the actual output sentences?

[kucai]

you need to connect the NMEA out wire (and ground)  to a pc serial port (or USB converter thingy) on the back of a laptop. On Windows, you open hyperterminal, set it to serial port, specify connection parameters, and voila! nmea sentences!

There is also a program that I already forgot (try gpsresource.com or something which listed a lot of free programs related to gps stuff) which can filter out non related nmea sentences for you which is extremely helpful to me when I did a river survey before.

And BTW, if you are planning to do this on a boat, you are better off buying the connection wire from HB if it's cheap enough in your currency. Sure beats having to solder, tape and joint cables to make it work . 

[sonarMick]

thanks Kucai, I received my AS HHGPS connecting cable today and will connect up to a computer hopefully tomorrow. The cable came with a Y splitter cable as well but I don't think I need it. The ultimate configuration I'm trying to achieve is to:
- send GPS NMEA data from the external GPS to the 899SI so that exact positioning data is registered on this unit.
- send NMEA out from the 899SI to a laptop so that depth as well as the exact positioning data from the survey GPS is logged as the one data stream.
From what I can work out, to achieve this, I connect the survey GPS nmea out wire and its ground wire, to the green (NMEA in) and ground (black) wire respectively on my HHGPS cable - this should provide the survey GPS information to my 899SI.

If I then also connect the white wire (NMEA out) as well as the black ground wire again to the appropriate pins on my serial plug (via USB converter) for the laptop, then I should be able to access all the data?
Correct?
Does this diagram look right?
Thanks

- Mick

[Humminbird_Greg]

The wiring connections sound correct.

[kucai]

 the pro hath spokenth! 

[sonarMick]

Thanks Greg, I'll wire that up and see what happens
Regards
- Mick

[sonarMick]

So I got the data coming from the 899SI to the computer OK (no survey DGPS at this point in time, just the internal GPS antenna).

I notice from the NMEA stream that there is a consistent 4 second time gap between successive GGA sentences and there are 4 DPT sentences between every GGA (as well as other codes I'm not interested in). Admittedly, I'm just sitting inside with a very poor position fix and no transducer connected (it's pouring rain atm), so I'm not sure if this has something to do with it, but what I would like is for GGA and DPT pairs to be output as frequently as possible. The NMEA sentence sequence I was getting is:

$INGGA,094551,2851.8806,S,15335.8148,E,1,03,3.2,-3.3,M,,,,*32
$INZDA,094551,27,08,2014,10,00*5F
$INMTW,,*49
$INDPT,,*47
$INHDG,0.0,0.0,$INHDT,0.0,T*25
$INRMC,094552,A,2851.8806,S,15335.8153,E,0.2,349.4,270814,11.5,E*46
$INDPT,,*47
$INHDG,0.0,0.0,$INHDT,0.0,T*25
$INGLL,2851.8806,S,15335.8153,E,094553,A*2E
$INVTG,349.4,T,337.9,M,0.1,N,0.2,K*59
$INMTW,,*49
$INDPT,,*47
$INHDG,0.0,0.0,$INHDT,0.0,T*25
$INRMC,094554,A,2851.8801,S,15335.8153,E,0.1,349.4,270814,11.5,E*44
$INDPT,,*47
$INHDG,0.0,0.0,$INHDT,0.0,T*25
$INGGA,094555,2851.8806,S,15335.8153,E,1,03,3.2,-2.7,M,,,,*39

I realise I could use the RMC and GLL sentences to give me more frequent position data, but that's not ideal in my case as my software can only be set too look for position in one sentence.
On my old Navman years ago, I had the option to turn off the sentences I wasn't interested in (in my case HDG, RMC, GLL, VTG, MTW), which had the result of speeding up the rate at which GGA and DPT were output from the unit. Is there a s similar option with the 899SI? I couldn't find it.

Thanks

- Mick

[Humminbird_Greg]

No, there is no option to turn on or off any of the NMEA sentences individually.  With the Humminbird units it is either all on or all off.

[sonarMick]

Thanks Greg, I suspected so. Would hooking up my 899SI via ethernet improve the update frequency (i.e. the number of GGA sentences per minute) ?
If so... from what I gather the 899 is ethernet ready, but I'm not sure how to go about setting that up.

[Humminbird_Greg]

I don’t think that an Ethernet connection will speed up the GGA sentence delivery sonarMick.

[sonarMick]

OK thanks Greg,
- Mick

[xSilmarilSx]

I think NMEA protocol specofy the time frame for the update.. Like once every 4 second...

If you already have the GPS input into the sonar. The unit can do live recording on the SD card without having the need to output all the data to log on a PC..

And the unit will record the entire sonar stream. So you can check your data more precisely after the data capture. Because you will have erroneous data point you will have to erase/modify.

Check ReefMaster for your complete solution in mapping.

[sonarMick]

I think NMEA protocol specofy the time frame for the update.. Like once every 4 second...

If you already have the GPS input into the sonar. The unit can do live recording on the SD card without having the need to output all the data to log on a PC..

And the unit will record the entire sonar stream. So you can check your data more precisely after the data capture. Because you will have erroneous data point you will have to erase/modify.

Check ReefMaster for your complete solution in mapping.

Thanks for the reply. I had a sounder years ago that had NMEA sentence frequency that was dependent on how many sentences were selected for output. With just GGA and DPT, it was putting out data on about 1 second cycles. So I'm pretty sure it is brand/unit dependent.
Regarding the live recording, I have used this however, as far as I know, NMEA data cannot be recorded to an SD card. Is this right? It would be fantastic if this was possible. The reason I specifically want NMEA data, is that GPS antenna altitude is captured in the GGA sentence. (I need to subtract depth and 'ducer offset from the survey GPS altitude to give real elevation of the seabed irrespective of tides, etc.)
I've been in contact with Reefmaster. Looks like a nice program. Unfortunately it can't utilise the GPS antenna altitude info.
Regards
- Mick

[kucai]

recording NMEA was put into the 'wish list' quite a while ago.. not important enough I guess.  :(