U/W Video Survey Overlay

[DennisS]

I'm preparing to do some reef surveys using a towed camera. I've seen quite a few units that will overlay GPS lat, lon, SOG and COG on the video tape in the $200-300 range. I am looking for a unit that will overlay a second NMEA sensor-Depth along with the GPS sentences on the tape

Here's an example of the single sensor GPS interface

http://www.icircuits.com/prod_osd_main.html This has a unit that will do GPS but no provision for a second input to get depth on the videotape

Does anyone know of a stand alone overlay interface that will take two sensors and is priced in the hundreds, not thousands.

 

[Bill51]

From what I understand, NEMA data streams can be combined with a simple hub and all data from all devices will be available simultaneously. The issue I see is getting the on-screen circuit to not ignore the depth data, and that’s going to be something programmed into the display decoder.

 

[ChrisA]

From what I understand, NEMA data streams can be combined with a simple hub.

It looks like the "geostamp" will do the job for you assuming that you first combine the NEMA data outside of the geostamp. But NO. NMEA data can NOT be combined with a "hub". It is a little harder thanthat. For practical purposes NMEA is just 1200 baud ASCII serial data. A combiner has to read two streams into a small queue and then empty the queues into a third output stream. Smarter combiners can be programmedto filter data from each stream.

You can buy these from several source for on the order of a couple hundred bucks or less but if you have a small computer with enough serial ports writting the software is not total rocket science.

Go to google and enter two words "nmea combine" without the quotes and you will get many hits. Here is one of them that is well known http://brookhouseonline.com/index.htm There are others

One other option is to remember that modern digital video camers record "time code" on the tape. Every frame will have the date, time and frame number recored on it. If you record the NEMA data to a computer you can match it up later.

 

[Bill51]

CruzPro makes a strong little combiner as does Noland Engineering and it will also output to standard RS232 to a computer for cleaning up or modifying the data. This could be handy if your overlay device ignores for instance depth but has another field you aren’t using you can send depth to it as something else. Both units are under $250.

I haven’t used any yet but I understand some of the newer GPS units have multiple NEMA ports on them and they have a limited combiner/multiplexer function built in as well. I think it was one of the Garmin units that the GPS has a separate NEMA input for depth and it outputs a combined data stream on it’s NEMA output channel.