On 10/10/19 00:40, Simon Ritchie wrote:
The real question, really, is why you're aiming for that level of
precision
That's what the emerging equipment does.
For 'precision' i.e. repeatability then simply monitor the indicated
position over a short time frame - where the satellites used remain
constant. The change in position is your 'precision'.
This does not take into account the corrections that are needed for each
satellite that change with time, and corrections for the atmosphere that
changes with time.
So I expect the data you collect will be worse that the actual equipment
performance due to the lack of these corrections. Unless you pay real
money then your stuck with that.
I'm just planning on showing how it can be put together, but I'd like
to be able to say with confidence that it works properly.
As to who will use it, there's the readers of this forum, or some of
them, and surveyors and architects, of course. There's also
archaeologists, because they are required to log where they find
objects, and they use GPS trackers to do it. They often leave objects
in the ground to protect them, and then come back a few years later to
have another look using new techniques. It would be nice if they knew
precisely where their target is. They would only have to dig a small
hole to find it.
Usually there are 'bench marks' that professional surveyors used (past
tense in the UK) as a stating point to do their surveys. I know where
some of the ones around me are .. but I have no UK source as I don't
know the local terminology there. These are far more numerous that the
trig points of OS.
I note your point about plate techtonics. My local archaeology group
recently re-excavated a site that was first excavated a hundred years
earlier. The records they had turned out to be quite misleading.
That was due to poor record keeping, but I guess over that time, the
UK might have moved around a bit. I recall that one end is rising and
the other is sinking.
However, when new equipment comes along, people find new uses for it.
We moved house a few years ago and I saw our Land Registry documents.
I was quite surprised at the rudimentary map that is the legal
definition of our property. I'm supposed to resolve a boundary
dispute with this? Now that land is so valuable, I can see people
demanding better, so the estate agent will walk around the boundary
with a GPS device and the result will be logged with your land
registry records.
In the future I can also see architects putting GPS coordinates on
plans, and builders using accurate GPS devices to do the initial
layout of the site. At 2 cm accuracy, they will probably have to
tweak the positions using better instruments, but if GPS speeds up the
process or makes it more reliable, they will use it.
.
An architect will work off plans, title deeds etc. They won't specify
lat/lon but the position on the land parcel, usually a distance from a
boundary.
A builder will employ a surveyor to get the thing located correctly,
unless they are certain of a boundary.
Builders work with tape measures not GPSes. They use tape measures now.
There is no improvement by going to a GPS and increased cost of
equipment and paying for the correctional data. Why would they add costs
to their business for no benefit???
Given the inaccuracy of the trig point locations, I can't even do that :(
The trig points are accurate. But need corrections applied that are time
variable. A good old school surveyor could do it...
Your equipment without corrections will not be as accurate as the trig
points.
Without corrections what you could measure is precision and that is that.
----------------------------------
Without spending the money on the corrections you may as well buy the
lower performance level equipment .. the overall result will be the same
and it should cost less.
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