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How accurate is the Database posiion?


#1

Hi all

Here is a little navigational detail to mull over.

I have taken to plotting each unique summit I chase onto Google Earth. I have noticed previously that the Google plot seems to vary from the actual summit.
Today I worked Chris/F8DZY/P on F/PO-252 which is shown on th database at 43deg 21min 32sec North 01deg 13min 51sec West. When plotted the position seems to be quite a way from the summit.

If you then put the mouse on the actual summit, which you can obtain by tilting the image through 90 degrees to obtain the view from the horizon, the position is shown as 43deg 21.29min 68sec North 01deg 13.57min 85sec West.

I realise this is a meaningless question in the great order of things and the database compilers did a superb job at the outset but the discrepancy in the positions amounts to quite a few seconds. It would not make a huge difference in navigating to the summit if you put the database figures into your GPS but if you were being searched for, it makes a big difference.

Anyone have thoughts?

In passing, I am mystified by Chris signing as F8DZY but posting as F4DZY. Is it huband/wife or father/son team? I am only a newbie and have to ask these mundane questions !!

Best 73’s
David/G4CMQ


#2

In reply to G4CMQ:

Today I worked Chris/F8DZY/P on F/PO-252 which is shown on th database
at 43deg 21min 32sec North 01deg 13min 51sec West. When plotted the
position seems to be quite a way from the summit.

The positions in the database are those supplied in the relevant Association Reference Manuals, in this case the French one. When the summit lists are created, there are a variety of sources available. In many cases the position given varies depending upon the source used, and, possibly, its original intended use. In the case of the French data, I know that all of the various “suspected” summits were checked against the detailed 1:25000 scale CD-ROMs available from IGN, but there can always be the possibility of error in transcription, or even in the original map data, especially in such mountainous regions as the Alps or Pyrenees. I must also say that I have found certain discrepancies in the displayed position and/or elevation in some of the Google Earth data, and I would certainly not wish to “put my life on the line” using that source alone!!

In passing, I am mystified by Chris signing as F8DZY but posting as
F4DZY.

Chris has recently upgraded his licence class, hence the change from F4DZY to F8DZY. In order to retain his existing data within the database, he has retained the old log-in.

73 de Les, G3VQO


#3

In reply to G3VQO:

Many thanks for the information Les. Very useful. Thanks also for the explanation regarding Chris.

PS You were another one I seemed to have followed around the bands yesterday!!

73’s
David/G4CMQ


#4

In reply to G4CMQ:

Hi David

I have found altitude information read from google earth to be unreliable, also it doesn’t always get the contouring of hills correct either - for instance I have sometimes found trig points that are known to be at summits don’t appear to be when viewed in elevation.

73 de Paul G4MD


#5

In reply to G4MD:

I have found altitude information read from google earth to be
unreliable,

The height information in Google Earth comes from a separate data layer to the images. The images are flat, and are projected onto a surface computed from the terrain layer in software. The resolution of the height information is likely to be very different from the resolution of the image, so it is not a suitable tool for the determination of the precise position of a summit.