ardupilot goes into the water Part 6

From the numbers to the pictures.

We took all the NMEA data from 10ths (feeled thousands) of test-drives and concatenated them into one big file, we then converted to the UTM/depth representation as mentioned in the previous episode.

This file was finally fed into a MatLab script, that produced a 3D image, where the depths are represented as colors, ranging from red to blue. Red was 0m and blue the maximum depth of this (shallow) lake with about -11m. MatLab does an automatic adaption of the colors and the axes in this case. In the first run, the x and y data (resp. Easting and Northing of UTM) were also plotted in blue color. The derivated picture looked like that.

This is not very spectacular, because the whole picture is covered with blue lines.

The next one is without them:

This Picture shows the color-of-depth-representation only, and the aspect ratio is now about to be correct. (sorry, these are only screenshots)

This "Pizza Margherita with blue Curacao"-like JPEG will later on be the overlay for the Google-Earth representation.

But first, a 3D view of the lake:

This view is from below, looking up, so the "deep-Spots" in the lake are better visible. The spikes on the right side are depth-artifacts, coming from the launch-point, where the sonar transducer hit the ground.

There are three "deep" holes in the lake, they go down to about -11m, but the rest is in 3-5m range covered with waterplants, which gives a "billowing" effect in the orange and red area.

I think this view can be improved by changing the color scheme and putting a grid over it. (some new project for Jochen...).

Now back to Google Earth.

In GE, there is an overlay feature, that lets you mix the GE view with a picture. Now we have a picture, but how putting it all together getting it matched in terms of size and aspect ratio?

First of all, i activated all tracks, that we have produced in the past (the GPS Vizualizer thingy - you remember?). This will give us a picture like that:

Then, we activate the Overlay function in GE and take the picture with the blue lines as overlay. After adjusting the transparency, we can see both pictures. And then we can tear,push,shove and move the picture until it matches the tracks. This overlay we keep. Then, we do the same with the other picture (The Pizza-view) and take the overlay, we created before as a reference. So we arrange an overlay over an overlay over an overlay. Quite strange, but it works. This last overlay is THE overlay. If we save it as a .KMZ (not .KML!!!). We can distribute it to anybody who wants a quick pizza-service on Google earth.

So it looks like, before the matching of the overlays:

This is the picture it looks like, when all is done.

I try to provide the .kmz file here as a reference. (i splitted up the picture and the depth legend, so the legend can be placed anywhere.

Gurrensee_TP.kmz

Back to reality:

We tried it out on the next weekend-dive we had in the lake. We took the course from the launch-point to the "big-hole" on the leftmost side from Google-earth (the ruler-function), adjusted our compasses to that course and we hit the hole exactly!

Theory and practice in perfect match - that´s rare.

This was the Past. On my first blogpost on this site, a member (Tom) gave me a link to a swedish company which provides a software that does all the above with a few mouseclicks and the 3D representation looks even better. I tried the demo in the last days and it looked good. I think i will spent the 99 Euro-bucks and try it out.

Is anybody out there who has eventually experience with that Software?

It is called DrDepth: http://www.drdepth.se/

This is not the end of the story...

I think there will be another episode. Maybe you remember the oscillations on the plots? The solution to that will be posted next.

Here is a sneak preview:

Fighting with the Integrator, the NMEA parser bug, and a new platform...

Bye bye fire-brigade ship have a nice stay on the cellar shelf with Ken.

Harald, myself and a colleague made many surveys of very large reservoirs in Nigeria using rapid and lightweight methods in the mid-90s. One important piece of information in these surveys was the shoreline survey. This was done by a walkround with a handheld GPS or from satellite imagery (maybe Google) or 1:50,000 mapping. The waters along the shorelines of the reservoirs were often inaccessible due to reeds and the like and there were many creeks and tributaries that needed some compensation in voulme calculations. So some idea of the shoreline gave the reservoir model a better shape. Our work was for hydrological studies to route floods through the reservoirs and determine capacity. In large catchment reservoirs it is surprising how seemingly little effort was made by the consultants who designed the reservoirs to determine the actual impounded volumes. It was no less surprising that some of our surveys were tweaked or rubbished by such consultants to justify the construction of unecessary dams/

For that work and for much of the marine survey work I have done since I have used Golden Software's Surfer. DrDepth seems more intuituitive that Surfer and I will be downloading the demo to try it out. Surfer is quite flexible in terms of data input formats and that will be something I will be looking at and it does have many nice features for analysis and presentation.

Cheers,
Mike

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Comments

Harald Molle April 6, 2010 at 11:02am

@Mike,
Yes, you may be right. I also think, that a model-sized ship is not able to survive a longer journey on the sea.
Too high waves and the wind will make it impossible. Anyway, If you take the model with a bigger ship to the area of survey, and use the small ship as a robot, small "squares" of water may be surveyed (about 1k * 1km). The advantage of a robot-like ship is, that the straight-line behaviour is better than with a bigger (manually operated ship), assumimg friendly enivronmental conditions.
And the CO2-Emission figures will also be much better tham with a dinghy h:-)

The hull speed of the fire brigade-ship was indeed the problem. with about 1, length, i was close to the theoretical limit, which was about 5.5km/h.

Therefore (and for better stability), i built the Catamarane, which is described in the next Episode.
With that ship i also reached a "limit" at some 5.5km/h. Maybe, a better shaped hull will make it better.
Mike April 6, 2010 at 2:52am

Harald, other than as a exercise I dont think that a small UAV model is ideal for surveying large bodies of water. For the cost of a small dinghy and outboard you would have a much more stable platform and if you are going to use the UAV on a large body of water then you are going to need a recovery vessel anyway - just in case. You will also need to have a couple of guys on standby and for much longer as due to the very low hull speed of the model it will take much longer and require more man hours. The advantage of the model boat system is, in my opinion, for small ponds and calm waters. I have a video somewhere from about 5 years ago of a larger model boat (I think around 8' LOA) fitted with RTK and a multi-beam sounder and even that was intended for calmer and smaller waters.

What kind of speeds are you getting from your present model?
Harald Molle April 5, 2010 at 5:49am

At the moment there is no compensation, the data is taken as it is. The cone of the transducer is 30° (have to read the manual to verifiy if its really true). The DrDepth software i will test in the next days has a compensation feature for that. The actual measurements were done on a very shallow lake, so the wobbling of the ship sould not be a problem.
Lake constance is already on the list :-), but i think there will be some legal issues cleared up first, before launching a UAV into this lake.
The crossing of the Lake between Überlingen and Wallhausen should be possible with no problems with the actual battery capacity and speed. Maybe one day...
OpticalFlow April 5, 2010 at 5:31am

Hi. Nice work and makes for nice reading.

Do you compensate for the longer path when the boat tilts and rolls and the sonar doesn't look straight down ? (I guess the emitted beam would be at an angle ? But maybe the echo sounder it is just a point source and depth is measured by the time of the first return signal ?)

When will you profile Lake Constance ? :-)
Harald Molle April 5, 2010 at 5:06am

Hi everybody commenting my blog.
Thanks for the various hints regarding the vizualization software. I will have a closer look if business lets enough time in the next weeks.
The Software will surely be made available, but i have first to make some cleanups, that will it make better readable and/or adaptable to other users.
bigkahuna April 4, 2010 at 5:56pm

Harald, will you be sharing details about how your autopilot system is set up and perhaps your code? I'm considering a similar project, although I may opt to hack a commercial boat autopilot like the Navico TP10 instead.
Mike April 4, 2010 at 3:29pm

Harald, myself and a colleague made many surveys of very large reservoirs in Nigeria using rapid and lightweight methods in the mid-90s. One important piece of information in these surveys was the shoreline survey. This was done by a walkround with a handheld GPS or from satellite imagery (maybe Google) or 1:50,000 mapping. The waters along the shorelines of the reservoirs were often inaccessible due to reeds and the like and there were many creeks and tributaries that needed some compensation in voulme calculations. So some idea of the shoreline gave the reservoir model a better shape. Our work was for hydrological studies to route floods through the reservoirs and determine capacity. In large catchment reservoirs it is surprising how seemingly little effort was made by the consultants who designed the reservoirs to determine the actual impounded volumes. It was no less surprising that some of our surveys were tweaked or rubbished by such consultants to justify the construction of unecessary dams/

For that work and for much of the marine survey work I have done since I have used Golden Software's Surfer. DrDepth seems more intuituitive that Surfer and I will be downloading the demo to try it out. Surfer is quite flexible in terms of data input formats and that will be something I will be looking at and it does have many nice features for analysis and presentation.

Cheers,
Mike
Zak April 4, 2010 at 9:28am

Awesome. Keep up the good work.
3D Robotics

Chris Anderson April 4, 2010 at 9:19am

Ah, now I see. I was confused by the blue at the shore. Makes perfect sense now...
Harald Molle April 4, 2010 at 8:34am

Hi Chris
The marketing title should be "Google-Lake"
we can try to sell this name to the Google guys for tons of money!
The color scale should be right.

deep is blue is bottom

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