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ZFT
10th Feb 2004, 07:27
Does anyone know what the resolution of EGPWS is? Would you expect the real geographic outline of say an island to be accurately depicted on EGPWS or would the low elevation coastal areas not be displayed?

Thanks

None
10th Feb 2004, 10:34
Just checking, but you are aware that it is not a radar image, aren't you?

McD
10th Feb 2004, 11:24
There are different makers and versions of EGPWS, with different options, so what I say here may not specifically apply to each aircraft with EGPWS. However, to answer your question: no, with basic EGPWS, you won't normally get an "outline" of an island or coastline*

As NONE says, it's not a radar depiction. Rather, it uses information from three different databases (terrain, obstacle, and airport) to give you a display.

This display will normally show terrain within 2000' below the aircraft altitude. There are other features which will show high terrain, if you're in a high terrain area, regardless of the relationship of terrain height to aircraft altitude.

*There are exceptions to this:
a) if you're flying low enough to be within 2000 of the coastline, for example, or
b) there are some types of EGPWS features/options/interface software which WILL show both water and terrain (therefore, in effect generating a depiction of a shoreline). However, I've not flown in an aircraft which uses that sort of EGPWS feature, and I don't know which airlines/aircraft do have it.

ZFT
10th Feb 2004, 14:04
None/McD,

Thanks for your replies. Yes I’m fully aware that it’s not a radar image.

Let me expand upon my problem. We have just installed a Honeywell EGPWS onto a Level D simulator.

Everything works fine but, below 2000 ft the EHSI displays an effective, but inaccurate depiction of the terrain. I am wondering whether this apparent difference between the EGPWS and the visual scene (which is modelled from Satellite data and should therefore be fairly accurate) is due to the resolution of EGPWS i.e if the resolution is say 20 feet then low lying coastlines would appear to be incorrect.

I’ve searched, but cannot find a definitive statement on vertical resolution of EGPWS and was hoping that a true 'end user' may be able to advise me.

alf5071h
10th Feb 2004, 18:01
ZFT, EGPWS simulator installations have occasionally been problematical, but not as you indicate. I suggest that you contact Honeywell via www.egpws.com. There is a very knowledgeable and helpful team there.

FE Hoppy
14th Feb 2004, 01:50
ZFT,
it depends on what egpws system you have installed.
Do you have Low Density Cyan sea level displayed?
If you do then the coastline should show as the boundary of this region. All other colours are ref. aircraft geometric alt and therefore will change with aircraft at. So the area of low density green is not the coast. If you get what I mean.

swh
14th Feb 2004, 02:18
ZFT,

The best DEM (Digital ELevation Model) that is around at the moment would be around 100 meter tiles, anything smaller than that you are getting into the military quality data, or satellite radar sounding, and that gets expensive, not only for that data, but for the storage, and processing of the large amount of data.

I was of the understanding they use something like 100 m for the open areas, and supplement this high res contour information around specific airports.

Shoreline data that most people use is called GSHHS (
Global Self-consistant Hierarchical High-resolution Shorelines) the derivatives of that dataset I would see them using would be either the high resolution (0.2 km) or interm resolution (1.0 km)

ZFT
14th Feb 2004, 07:51
Again thanks for all the responses.

I believe the answer to my original query lies within a statement from The EGPWS product spec (and I must say that Honeywell are being very helpful) which states:-

Terrain is NOT shown if it is more than 2000ft below reference altitude and/or is within 200ft (400ft prior to –218) of the runway elevation nearest the aircraft“

This would seem to indicate that coastal/island airfield would not show a too accurate coastline depiction.

Loads more reading/research to do though