Frustration with Elevation

[gojozoom]

Hi guys,

I do a fair bit of mountain flying hence a precise vertical profile is a key part of my flight planning process.

Here is an example of my issue: When you fly from Paraparaumu straight to Masterton you'll have to fly over Mount Hector which is 5014 feet high. According to Plan-G (using the NOAA tiles) it's only 3200 feet, so if I trust that DEM I'll end up as a crash site on the side of a mountain...

I "could" use Google Earth (that seems to have correct elevation data) but it lacks all the features provided by Plan-G.

I found free hi-res DEMs for NZ here and asked on the Plan-G forum if there is a way to import them but there was no answer.

Any ideas what to use for precise vertical profile planning?

Dan

[NZ255]

Nevermind I didn't read the question

[Fozzer]

Problems with elevation?... ....!

"Viagra" cures all!..... ...!

Paul.... ...!

[Ian Warren]

Trust you Paul !

[gojozoom]

I knew you guys would help My elevation problems are all sorted now!

Seriously now, is there any ways to extract precise elevation info from FSX itself?

[Ian Warren]

This is were we get these elevation problems across the board, Paraparumu is fixed with that little flatten , never thought to check even the Christchurch port hills , my brother fly's from there regularly with his hang glider and has full instruments least for a hang glider giving good and exact elevations, I'll get him to do check and write down alts , I then can compare them in FS , a full mesh I requires one to no the heights to compare.

This dose to be a continuing saga , how accurate are these meshs ?

[gojozoom]

I'm using ORBX NZ so it's a 10m mesh. I tested it at random mountains and valleys and it seems to be all correct. So it's all good in the sim, it's just not so good in flight-planners.

[Ian Warren]

Its not really a 10 meter mesh, sorta twisted and reason why so many airfields have these elevation issues - best example was Foxpine were with VLC the levels matched the AIP - install ORBX and that little field has rising a good 3 meters .... surprised the flight planners do pick up on these levels as your pointing out.

[toprob]

It should be an easy question to find the answer to -- where does Plan G actually get its elevation data from? Sorry I can't help, but the manual states in 'features':
Vertical Navigation profile (requires additional Digital Elevation Model(DEM) download)
...so I'd assume that you have downloaded this? I wonder what format that is in? Once you know that, it should be easy enough to figure out if it can be replaced with something more accurate.

It doesn't really make sense to me that it shouldn't be accurate enough for navigation, though, as most available data is within certain tolerances, so even a rough low-res mesh should still have accurate vertical data points. The only thing I can think of is that they squash it so much (to include the whole world in a managable download maybe?) that it becomes something like the old FS2002 mesh, where 'small' mountains became hills...

QUOTE (Ian Warren @ Oct 22 2014,3:36 PM) <{POST_SNAPBACK}>

Its not really a 10 meter mesh, sorta twisted and reason why so many airfields have these elevation issues - best example was Foxpine were with VLC the levels matched the AIP - install ORBX and that little field has rising a good 3 meters .... surprised the flight planners do pick up on these levels as your pointing out.

Although it's not entirely relevant to the question here, my understanding is that Orbx's NZ mesh is based on this data:
https://data.linz.govt.nz/layer/1768-nz-From the LINZ site:
"Spatial accuracy is nominally the same as for the LINZ source data: 90% of well-defined points are within ±22 metres horizontally and within ±10 metres vertically." So, really it is a 22 metre mesh, extrapolated to 10 metres. However, once again the vertical points should be good.
There are a few good reasons why this is extrapolated -- mainly because resolution is the only way to control which mesh is displayed, the higher resolution mesh always wins, so you can always expect that the Orbx mesh will display. The relationship to the AIP elevations is a different issue, the AIP elevation tends to be the highest point at the airfield, so it may not be the best elevation, but having a fixed elevation for an airfield certainly makes it easier to design addons for. So I prefer VLC's DEM which blends to AIP elevations, rather than chops them or places a plateau. Of course Orbx don't expect you to use non-Orbx airports, so their system helps to shut out addons which don't specifically adjust for the Orbx DEM.

[scaber]

QUOTE (toprob @ Oct 22 2014,5:00 PM) <{POST_SNAPBACK}>

It should be an easy question to find the answer to -- where does Plan G actually get its elevation data from? Sorry I can't help, but the manual states in 'features':
Vertical Navigation profile (requires additional Digital Elevation Model(DEM) download)
...so I'd assume that you have downloaded this? I wonder what format that is in? Once you know that, it should be easy enough to figure out if it can be replaced with something more accurate.

......

I, but having a fixed elevation for an airfield certainly makes it easier to design addons for. So I prefer VLC's DEM which blends to AIP elevations, rather than chops them or places a plateau. Of course Orbx don't expect you to use non-Orbx airports, so their system helps to shut out addons which don't specifically adjust for the Orbx DEM.

Good explanation Rob. Thanks for that. The other thing that occurs to me is that if you are flying so close to mountains etc that you are depending on a 3m accuracy then you are doing something seriously wrong with you separation requirements!

[emfrat]

QUOTE (scaber @ Oct 22 2014,7:19 PM) <{POST_SNAPBACK}>

Good explanation Rob. Thanks for that. The other thing that occurs to me is that if you are flying so close to mountains etc that you are depending on a 3m accuracy then you are doing something seriously wrong with you separation requirements!

Grump, Grump - isn't that half the fun?

[gojozoom]

No-no-no, I'm not looking for such crazy accuracy, but calling out the difference between the 3200 feet (downloaded DEM) and 5000 feet (ORBX) is not really nit-picking, is it?

Anyways, as Rob suggested, I'll do some research on DEM data and find out what format Plan-G takes, and convert the hi-res one to that format.

Cheers
Dan

[Ian Warren]

In the computer world you cannot kill yourself tho as hard as we try, fact is in the real world the amount off very experienced pilots and nav's flying eyeball navigation a hill suddenly pops up in front off them and getting themselves killed, so in a way the elevation levels only really affect me into airports .. I think and always give myself a good margin in FS, wonder ... that would be healthy in real life.

[gojozoom]

Yes, of course, I don't actually need precise elevation data to be able to avoid mountains in a VFR flights but you have to factor in the performance of your aircraft. Like this scenario:

You have a fully loaded DC-3 that you have to fly from A to B with a mountain range in the middle. I'd really like to know if I'll be able to climb enough to clear the mountain or I have to go around it. Now I should be able to climb 5000FT in 10 minutes and if I follow the incorrect DEM that shows 4500 feet for the mountain top where it's really 6000 feet then I end up with screaming passengers and very low FSPassengers score

Anyways, once I work it out I'll let you all know. Funnily enough, the NOAA site is down at the moment....sigh

[Ian Warren]

I got that Air Hauler program that was on special from Just flight , rather the crashing into the hills and mountains, Id rather get my plane load off cabbages to Milford Sound for that $14.805.00 check