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adhawkins
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It's something like 'Kemble to Cranfield'. Ok, I obviously won't be doing that much, I'll try to get it from the file name. Andy
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Tim Dawson
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I can't remember what's in the name tag. Is it a friendly description of the route? If so, I expect SkyDemon is looking up whatever waypoints lie close to the start and end positions of the flight log.
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adhawkins
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Group: Forum Members
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Ok, seems like I had the right idea then. Finally, where does it get the text that it puts in to the 'name' tag of an exported GPX file? Is that parsed from the filename also?
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Tim Dawson
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The filename itself should include the start time on old files. Failing that, we use the creation time.
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adhawkins
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Returning to this after a holiday with another question. The first line of most of my GPX files is something like: #START=20130810122930 This is easily parsed into the start time of the file. However, I've found some old files that don't have this line, but the timestamps within the file still start at zero. SkyDemon know when this flight started if I open it, presumably it's getting this from the timestamp in the filename? This timestamp doesn't assume seconds, so I have to assume they're zero. Is this the correct approach? Andy
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adhawkins
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Excellent Tim, thanks for confirming that. Andy
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Tim Dawson
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Fields are:
Elapsed time (milliseconds)
Position
Track (degrees true)
Speed (knots)
Altitude (feet)
Vertical Speed (feet/min)
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adhawkins
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Ok, getting there I think. All looks good, but for some reason my latitude calculations don't quite match up with SkyDemon's, I'm often one or two digits off in the 6th decimal place. I don't think that's significant, but I can't understand why! I've attached 3 files, one .flightlog file which is the source. Then there's a GPX file (the one without ADH in the name) that is the file converted using SkyDemon. Finally another GPX file (with ADH in the name) which is converted using my utility. If you look at the first latitude in the file, in the source file it's: N514241.70 Which is 51 degrees, 42 minutes, 41.7 seconds north. I'm converting this to decimal degrees using: decdeg = deg + mins/60 + secs/3600 and I get 51.711583333333333333333333333333, which I round to 6 decimal places to get 51.711583. However, the measurement in SkyDemon's GPX file is 51.711580. This trend follows throughout the file on the latitude fields, but the longitude fields (converted in exactly the same way) tend to be correct. Anyone offer any suggestions as to what I might be doing wrong?
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adhawkins
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Thanks for that Steve, seems to agree with my findings from reading the file. I've found the GPX spec, and also looked at the GPX files that SkyDemon generates, so should be Ok now to proceed with the conversion. My aim will be to produce a file that's near identical to the one SkyDemon generates when it does the export. Would be nice if Tim could just confirm our findings, particularly in terms of units used.
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stevelup
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Field 3 is the heading (a trip from Oaksey to Oaksey started and finished with it reading 23 for me, and the runway is 22) Filed 4 appears to be in kts (my climb out is reading 65-75, cruise 115-120 and approach 55-60 - all of which are correct assuming it was a calm day) Field 5 is definitely in feet (my start and end readings for the above trip are 270 and 272 ft)Field 6 appears to be vertical speed - in that the start of the trip has positive numbers, the end of the trip has negative numbers, and the middle is mostly zero. The null range on this seems sticky - it doesn't report slight deviations, only significant ones. To convert to GPX, all you need are the co-ordinates and altitude - and possibly the timestamp?
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