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Old Apr 24, 2012, 01:54 AM
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Sweden, Stockholm County, Sollentuna
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Software to analyze altimeter data?

I have bought Fly Dreams altimeter from Hobby King (http://www.hobbyking.com/hobbyking/s...dProduct=22630) and am very happy with it. It is a rather cheap altimeter, but it does what it is supposed to do in every way. The only tiny little drawback is the PC-software, which is adequate, but doesn't excell. As you can see in the attached screendump the software has automatic peak-find, it has manually adjustable "time-bars" which lets me measure time-distances. It has a tool to set marks on the curve, which eases reading height-differences.

All this is fine when analyzing a few flights, but I was out flying yesterday and had a lot of rather short flights. To analyze those with FlyDreams tool is quite cumbersome, so my question is: Can anyone recommend any (freeware) software to analyze flight data?

What I need from the software is:
  • It should be able to read comma separated values (FlyDreams software can export to csv-file)
  • It should be able to plot the curve
  • It should allow me to mark two points on the curve and would then report Xdiff, Ydiff and gradient

I don't have access to Matlab, but I do have Scilab. I tried to write a function to perform the analysis, but it became rather obvious that I'm not skilled enough to do it. Is that the best way to go? Or are there other softwares out there that are more suitable for this rather simple analysis?

I look forward to any hints or advices

/Stefan
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Old Apr 24, 2012, 03:26 PM
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You get what you pay for ...
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Old Apr 24, 2012, 05:33 PM
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Have you tried Excel? I know it will do the first two but I would have to play with it a bit to see of it would do the third, but I'm willing to bet it will.
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Old Apr 24, 2012, 06:04 PM
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Originally Posted by Windrider53 View Post
Have you tried Excel? I know it will do the first two but I would have to play with it a bit to see of it would do the third, but I'm willing to bet it will.
Excel will likely do what you want ... but these aren't the most basic charting exercises so it will take some experimentation I suppose.
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Old Apr 26, 2012, 04:09 AM
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Originally Posted by Windrider53 View Post
Have you tried Excel? I know it will do the first two but I would have to play with it a bit to see of it would do the third, but I'm willing to bet it will.
I have never used used any interactive plotting in Excel (is there such a mode?), nor have I ever programmed any excel-macro, so the start-up is a bit too high for me. Besides, I'm mostly running Linux, but I guess OpenOffice/LibreOffice have everything Excel has....

There is a program called QtiPlot that does what I want, but it is still a little bit too much manual labour to get the figures I want.

Yesterday I began (once again) writing a Scilab-script. So far I've managed to:
  • Read the csv-file
  • Plot the curve
  • Let the script wait for two mouseclicks and thereby selecting a subsection of the curve
  • In that subsection find the local maximum (maximum height) and maximum climb-rate.

Still left to do is:
  • Find a good algorithm for computing minimum sink-rate
  • Learn how to draw annotations in the graph for Max-height, max-climb and min-sink
  • Write some logic to let the user repeat the subsection-selection
  • .
  • .
  • .
  • Learn how to read the fda-file


I'll let you all know when (if?) the script gets in a shape good enough to share.

/Stefan
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Old Apr 26, 2012, 05:32 AM
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Originally Posted by SBS_Pilot View Post
I'll let you all know when (if?) the script gets in a shape good enough to share.

/Stefan
If you get this in a user friendly form there are other altimeters that produce csv files that need better software for viewing results. I for one am interested in seeing what you come up with.
Thanks
Kerry
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Old Apr 26, 2012, 09:02 AM
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Old Apr 26, 2012, 11:53 AM
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Originally Posted by rc4fun View Post
If you get this in a user friendly form there are other altimeters that produce csv files that need better software for viewing results. I for one am interested in seeing what you come up with.
Thanks
Kerry
I can try to adopt the script to more datafiles than the FlyDream-format. You are very welcome to upload a file of your own here, so I get more test data. If you do - please state which data is in each column (unless it's the trivial case with only two columns).
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Old Apr 26, 2012, 01:40 PM
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Originally Posted by SBS_Pilot View Post
I have never used used any interactive plotting in Excel (is there such a mode?), nor have I ever programmed any excel-macro, so the start-up is a bit too high for me. Besides, I'm mostly running Linux, but I guess OpenOffice/LibreOffice have everything Excel has....

<SNIP>
/Stefan
Excel will plot graphs of your altitude profile with no programming whatsoever. It will also allow you to mark points manually, but it gets a little more involved for more sophisticated functions - - - but still do-able. I wouldn't characterize Excel graphing as "interactive plotting". If you want "automatic" (i.e. no manual intervention) graphing for each set of data, an Excel macro will likely be required. Check around the web for one - it may already be done.

I have no experience with OpenOffice, but I'll bet if you dig around on the web you will find information to help.
Curt
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Last edited by CurtissP40; Apr 26, 2012 at 01:45 PM.
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Old Apr 27, 2012, 04:11 PM
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It turned out that the code I originally wrote wasn't unnecessary easy to expand to a more automatic analysis, so I rewrote it. And, of course, I accidently deleted it! And to make things worse I had worked in my temp-directory, which I haven't any back-up on. And the final blow was that since I am on a Linux-system, a deleted file is deleted.

So I have to begin from the beginning once more, but I hope it will go faster this time because I am now aware of some of the pitfalls along the way...

Anyway. I began to thinking of a few things that I have taken for granted until now:
  • How to define climb rate?
  • How to define sink rate?
  • How to define launch and landing?

When measuring manually I inspect the curve and drav a line where the curve is steepest (climb) and flattest (sink), but when automating that just isn't sufficient. Instead, this is my current approach:

I define a window-size, currently 5 seconds. At any given time T, the climb rate is ( height(T) - height(T-5) ) / 5. That calculation is repeated for every sample from launch up to maximum height, and the highest value is reported.

I do in the same way for sink-rate, but the window is 10 seconds and the timerange is from max-height plus ten seconds down to landing.

The FlyDreams Altimeter reports height as height above sealevel (i think) and not height above ground. At least that is what I think it does. I am getting 80m when the plane is prepared for launch, but I have no idea what the actual height above sealevel is at my local field.

Anyway, I try to correct that by calculating the median height of the first recorded 10 seconds and subtract that value from the recorded heights.

To detect a launch I look for when the height is above a treshold, currently set to 2 meter. A landing is detected when the height is below that treshold.

Here is a slight problem. In my testdata, the recorded height ripples a little bit, say +/- 2 meter. If I have the launch/landing treshold too low I may detect false landings when the pilot has restarted the motor very close to the ground. The measured flight-time will also be a little bit too short, especially on the occasions where the plane has had a very shallow glide on the last part of the landing. On the other hand: if the treshold is too low I will detect a few false launches when the values ripples above the treshold.

I look forward to any comments on this. Also please upload one or two csv-files to test the algorithms on.

/Stefan
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Last edited by SBS_Pilot; Apr 27, 2012 at 04:13 PM. Reason: Corrected the definition of sink-rate.
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Old Apr 27, 2012, 05:33 PM
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Google Earth will give ASL if you hover your mouse over your field it will display at the bottom right.
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Old May 05, 2012, 02:35 AM
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Originally Posted by SBS_Pilot View Post
What I need from the software is:
  • It should be able to read comma separated values (FlyDreams software can export to csv-file)


/Stefan
Hi

Can you please help me locate csv export option in FlyDream SW ? I can't find it.
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Old May 05, 2012, 02:37 AM
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OK, just found it.
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Old May 05, 2012, 03:47 AM
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Originally Posted by razkent View Post
OK, just found it.
It's well hidden, isn't it?
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Old May 05, 2012, 07:25 AM
dare to thermal
Mannheim, Germany
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checkout logview
http://www.logview.info/vBulletin/
You can alos contact the devolpers directly for help.

Bernd
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