[time-nuts] question about Thunderbolt geo acuracy

[Jim Lux]

On 5/11/12 5:23 AM, swingbyte wrote:
s disappointing!
>
> I need to measure the height of my house floor to be above the flood
> plane contour. I might have a look at some dted from work. Might have to
> pay a real surveyor to measure the height datum.
> Thanks for all the info though guys
>

for that, you need a real surveyor who can provide a "legally accepted" 
measurement.  Someone who can
a) know from the flood level definition what vertical datum they are 
using (probably NOT something normal in the geodesy world)
b) knows the legalities of establishing the difference

The mechanics of surveying (leveling in this case) are straightforward 
to learn.  The legalities and local practices in documentation are not. 
  This is what getting a Land Surveyor's license is all about.

There's also a question of what the legal height of your house is, 
relative to the property (from a flood insurance standpoint).  They 
might have some arbitrary offset in the rules. Sort of like how baseline 
electrical power consumption is actually about 2/3 of the expected 
minimum consumption in the area for a given size house and appliances 
(e.g. nobody is likely to consume less than baseline)

There are some mortgage servicers, by the way, who take property 
addresses that have been geolocated and FEMA flood plain definition maps 
to determine whether you definitely don't, definitely do, or just might 
need flood insurance.  The maps change (as does the geolocation). From 
what I understand, about 3-5% of the properties scanned require some 
sort of manual intervention (maybe the address doesn't geolocate, or 
it's right on the line, or)