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Help with my coordinates


#1

having difficulty editing / entering my location in sotawatch for summit distances / degrees. used ordsvy / javascript tried but wayout.

my NGR SO034061


#2

In reply to GW0VMZ:

Hi Alistair

I use http://www.archaeoptics.co.uk/coordinate-converter it seems to work well.

According to it your NGR translates to -3.3994, 51.7448

73 de Paul G4MD


#3

In reply to GW0VMZ:
Or according to google earth 51.7457 & -3.3986
Dont forget 6 fig NGR correct to nearest 100m
Steve.


#4

In reply to G4MD:
thanks paul, and steve inky job done
vmz


#5

In reply to G4MD:

I use http://www.archaeoptics.co.uk/coordinate-converter it seems to
work well.

A note of caution: this converter appears to be using the OSGB36 datum. This corresponds to the lat/long marked on OS maps, but for SOTAwatch, Google etc you want WGS84. The discrepancy will be of the order of a hundred metres; barely significant with a six figure reference but definitely worth worrying about with an 8 figure reference.

The most accurate online converter I know of is at

http://gps.ordnancesurvey.co.uk/etrs89geo_natgrid.asp

This uses the OSTN02 model and is error free by definition. Unfortunately it does not understand grid letters but requires full coordinates.

I routinely use GPS Utility (www.gpsu.co.uk) which to 4 decimal places got the right answer: 51.7452N 3.4006W.


#6

In reply to M1MAJ:
hi martin tried your coordinates local summits appear ok but new york for instance shows 232 degs from my qth when it should be 291 degs aprox on telnet and javascript and is about right if my memory serves me correctly from my dx days …


#7

In reply to GW0VMZ:

hi martin tried your coordinates local summits appear ok but new york
for instance shows 232 degs from my qth

I observe the same effect. I suspect the bearing calculation on SW2 is wrong.


#8

I tend to use http://www.carabus.co.uk/jscalculators.html

For conversions.


Stewart G0LGS


#9

The distance given by SOTAwatch is wrong too. I think Jon needs to check the code - it’s clearly not right as it stands.


#10

In reply to M1MAJ:

thanks for your assistance martin i had tried many times and used some of the advised web sites / programmes carabus / ordsvy etc as advised in these posts but i also noticed distances appeared wrong too . ( the kilometers for S AFRICA appears to be somewhere near IF it was given in miles instead)maybe there’s a clue there ?

73s gw0vmz


#11

In reply to GW0VMZ:

Hi,

This feature uses a very crude calculation that was done when we were just using grid references for the UK. I would have thought it will be way, way out when used for anything over a few hundred km.

I haven’t looked at it for a couple of years. I’ll take another look at some point and see if I can make something a bit more sophisticated.

73, Jon


#12

In reply to GM4ZFZ:

I’ll take another look
at some point and see if I can make something a bit more
sophisticated.

There are plenty of sites with suitable formulae, and even sample code. Search terms like “great circle distance bearing” will find them. However you have to be careful to find one that is numerically stable as well as mathematically correct. Some code that gives good answers for long distances can be very dodgy when the distances are short, and vice versa. The Wikipedia article has some useful background.

What language is this written in?