questions about elevations in ORBX NZSI

[DonMunro]

Hi everyone,
I normally fly sailplanes with UKVGA (UK Virtual Gliding Assoc) and several days ago I decided to fly a task from Omarama, NZ.  (plg file is attached)
As I was flying I noticed that that the mountain terrain around me seemed to be much higher than I expected... at least to my eye.

I didn't complete the task and "landed out"... my altimeter at that point was ~4500ft and I failed to clear a ridge that Plan-G said was ~2800ft. Later on I took my A2A Cherokee out and confirmed that many of the peaks and ridges are MUCH higher than Plan-G says they are.

I have been having good discussions on the ORBX & UKVGA forums about this and today one of the ORBX guys provided me with the attached Google Earth screenshot for a peak in the Omarama area called Snowy Top.

the following is a copy of what I posted at UKVGA and ORBX
==============
I just discovered a HUGE anomaly... I created a User Waypoint in Plan-G at the coordinates for Snowy Top (from attached GE screenshot)

S 44 24.327 = -44.40545 
E 169 45.952 = 169.76588 (Plan-G needs the decimalized numbers)

Plan-G says that the waypoint's elevation is 3192 ft  GE says it's 5654 ft

Stranger still is that if I check spot elevations right around the waypoint it says 4377 on one side and 4649 on the other (1000+ feet higher than the waypoint on the peak, but still 1000+ feet lower than GE)

I then thought... this is weird. I wonder if Plan-G's elevations are screwed up everywhere.
You will be relieved to know that the Pacific Ocean and the Tasman Sea are both at 0 ft 
BUT, spot elevation checks on various lakes in the vicinity of Omarama are all over the place.
===================

I have also attached a screenshot of the Waypoint Edit screen. That's where the 3192ft came from. Does Plan-G populate that field from the database or is it for input? I tried editing that value later but it cannot be changed.

Scenery loaded: ORBX NZSI, Global, Vector and FS Ultimate. Oceania set in FTX Central.
I also use Mapbox Terrain in Plan-G
Plan-G database is freshly re-built

Questions: is this a known bug when flying in NZ? Does it have to do with ORBX add ons? Is there a remedy?

thanks and sorry for rambling on
Don

[ivanrk]

Hi

I experienced the exact same problem.  I have ORBX New Zealand and fly regularly in the South Island around Queenstown Wanaka Dunedin Milford Sound etc.  I always fly 1500' above the highest point Plan-G gives me on its map.  However I regularly crash into the mountains unless I add dramatically more to my height.  Not sure where the problem lies but certainly the altitude provided in Plan-G cannot be relied upon.  I can only assume the error is within ORBX as I would be surprised if the altitudes we have downloaded into Plan-G are wrong.

Ivan

Added:  I created a waypoint at the exact same location as your and I have an even lower height showing.  Very strange and I do not know how to fix it as I assume Plan-G must use those g type files from NOAA.  I have attached my waypoint for comparison.

[tim arnot]

Sounds like a limitation of the DEM you have installed. You could always try editing it in an image editor (Paint, photoshop etc) - it's only a greyscale bitmap.

[ivanrk]

Not sure I understand your reply.  The DEM files I downloaded are a10g b10g etc.  These are not bitmaps are they?  Are these what you are suggesting we change?

[tim arnot]

Yup. That's all a DEM is at the end of the day - a bitmap.

If you can't open it in a standard editor, here is a list of programs designed to work specifically with DEM files.
http://softwaresolution.informer.com/Application-to-Work-with-DEM-File/

[DonMunro]

Sounds like a limitation of the DEM you have installed. You could always try editing it in an image editor (Paint, photoshop etc) - it's only a greyscale bitmap.

Hi Tim,
I really do not understand this... what does "a limitation of the DEM you have installed" mean?  Do you mean that the mesh is too accurate and that it should be flattened out? That doesn't make sense to me. We don't buy hi-def scenery so that NZ can look like the UK.

Why can't Plan-G simply report the data values that are in the installed mesh?

I also have ORBX PNW loaded and have not had any difficulties with that... plenty of high mountains there.

When I do a database re-build does it "flush" all of the old values and completely re-build the database or does it only update changed values?

Should I un-install Plan-G, remove all traces of it and then re-install it?

thanks
Don

[edit] I think I understand now... "a limitation of the DEM you have installed" means the NOAA DEM that's installed. I thought that you meant the enhanced scenery DEMs that are installed in FSX. eg ORBX FTX Regions or UTX etc, etc

[tim arnot]

The mesh installed in Plan-G is 1.2km

The mesh installed in FSX is 10m

Obviously the FSX mesh is going to be much more accurate.

Plan-G has no access to the mesh inside FSX, only its own.

[DonMunro]

Hi

I experienced the exact same problem.  I have ORBX New Zealand and fly regularly in the South Island around Queenstown Wanaka Dunedin Milford Sound etc.  I always fly 1500' above the highest point Plan-G gives me on its map.  However I regularly crash into the mountains unless I add dramatically more to my height.  Not sure where the problem lies but certainly the altitude provided in Plan-G cannot be relied upon.  I can only assume the error is within ORBX as I would be surprised if the altitudes we have downloaded into Plan-G are wrong.

Ivan

Hi Ivan,
Whew... I thought this was only me  :D
I think that you have it backwards in the last sentence... it IS Plan-G... as far as I can tell the ORBX scenery agrees very closely with reality. At least what Google Earth says is reality. Also, the water level on lakes varies by hundreds of feet in Plan-G. Find a big lake and do some elevation spot checks.
Don

[DonMunro]

The mesh installed in Plan-G is 1.2km

The mesh installed in FSX is 10m

Obviously the FSX mesh is going to be much more accurate.

Plan-G has no access to the mesh inside FSX, only its own.

Oh really???
WOW, I thought that Plan-G was reading the FSX, or whatever is installed data.
hmmm... that casts a whole new light on things

So we should only rely on Plan-G for navigational information and ignore the elevation output?

Don

[tim arnot]

No. Plan-G uses the data you downloaded from NASA.

[DonMunro]

Hi Tim,
Please clarify that... when did I download data from NASA?

cheers
Don

[edit] sorry about that... old-timers memory lapse  :P 
I did install some of the NOAA DEM files when I first installed Plan-G. I just checked and the L sector (NZ/Aust) is in the Plan-G DEM folder. I am now downloading the entire set and will replace the originals... on the off chance that they are corrupted.