[time-nuts] Lady Heather's Fat Client

Bruce Griffiths bruce.griffiths at xtra.co.nz
Thu Dec 10 02:37:14 UTC 2009


As far as I can tell from the Thunderbolt documentation the location is 
reported in WGS84 coordinates.
One then has to correct for the Geoid separation to get height above MSL.

My thunderbolt reports an altitude of +65m whereas google earth and my 
M12+T both report a height of +43m.

Bruce

Bruce Griffiths wrote:
> For more detail see:
> http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA407319&Location=U2&doc=GetTRDoc.pdf 
> <http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA407319&Location=U2&doc=GetTRDoc.pdf> 
>
>
> Bruce
>
> Bruce Griffiths wrote:
>> More accurately (pun intended) the GPS receiver first calculates the 
>> height above the ellipsoid that approximates the earth's surface and 
>> then uses a geoid separation table to calculate the height above MSL.
>> Due to storage constraints the geoid separation table may necessarily 
>> be inaccurate.
>>
>> Bruce
>>
>> John Miles wrote:
>>> That graphics library is 95% post-consumer fiber at this point. :(  
>>> It's
>>> good for rapid development and porting work but as you can tell it's 
>>> pretty
>>> rough around the edges.
>>>
>>> Every time I run a survey on a Thunderbolt here, it seems to want to 
>>> find
>>> itself at the bottom of the lake.  Bruce pointed out in an email 
>>> that what
>>> GPS considers "altitude" isn't necessarily the same as what terrestrial
>>> mapmakers mark as sea level, so maybe that's what's happening.
>>>
>>> -- john
>>>
>>>> -----Original Message-----
>>>> From: Mike Naruta AA8K [mailto:aa8k at comcast.net]
>>>> Sent: Wednesday, December 09, 2009 4:12 PM
>>>> To: John Miles; time-nuts at febo.com
>>>> Subject: Re: [time-nuts] Lady Heather's Fat Client
>>>>
>>>>
>>>>
>>>> Oh, I thought it was my PC.
>>>> Neat John, we like recycled code.
>>>>
>>>> The KE5FX remote access is fun too, works well.
>>>>
>>>> I'm surprised that your antenna receives so well,
>>>> being at -7.6 m.  Doesn't it get wet?
>>>>
>>>>
>>>> (I know; I'm just trying to be funny)
>>>>
>>>>
>>>> Mike - AA8K
>>>>
>>>>
>>>>
>>>> John Miles wrote:
>>>>> Hi, Mike --
>>>>>
>>>>> Correct, that's not a bug, and it won't change unless/until the
>>>> program is
>>>>> rewritten with a new graphics library.
>>>>>
>>>>> In fullscreen mode there's no window border, so the 1024x768
>>>> display surface
>>>>> can accommodate the 1024x768 client area.  When you hit F11 to
>>>> go back to
>>>>> windowed mode on a machine with a 1024x768 desktop, there's no
>>>> room for the
>>>>> window border and caption bar that surrounds the client area, so the
>>>>> graphics system has to downsample the client area to fit.
>>>>>
>>>>> Back when the graphics library was written, in an era when 33
>>>> MHz processors
>>>>> were still common, it was much faster to downsample by factors
>>>> of two than
>>>>> to incrementally shrink the image to fit.  So you will always
>>>> get the tiny,
>>>>> cramped display window in cases where you request a resolution in 
>>>>> window
>>>>> mode that can't fit on the desktop.
>>>>>
>>>>> -- john, KE5FX
>>>>>
>>>
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>>
>>
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>
>
>
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