rec.autos.simulators

by **Brian Whitso** » Wed, 12 Nov 1997 04:00:00

I have been playing CPR for about two weeks and have generally been
impressed now that I have got the steering and the setups sorted out.
Every sim seems to have a certain learning period. However compared to
Papyrus products, the Laguna track seems too flat. I don't have an
accelerator; does that make a difference? I know that Microsoft makes a
big thing about how accurate the tracks are due to their use of GPS to
determine elevations. However every mapmaker knows that when you are
scaling drawings it is general practice to exagerate the vertical dimension
by 2 or 3 times so that the change in elevation is more evident.

Brian Whitson
Community Planner

by **Jarrod A. Smit** » Wed, 12 Nov 1997 04:00:00

> I have been playing CPR for about two weeks and have generally been
> impressed now that I have got the steering and the setups sorted out.
> Every sim seems to have a certain learning period. However compared to
> Papyrus products, the Laguna track seems too flat. I don't have an
> accelerator; does that make a difference? I know that Microsoft makes a
> big thing about how accurate the tracks are due to their use of GPS to
> determine elevations. However every mapmaker knows that when you are
> scaling drawings it is general practice to exagerate the vertical dimension
> by 2 or 3 times so that the change in elevation is more evident.

> Brian Whitson
> Community Planner

This also brings up an interesting technical point about the way they measured
the tracks w/ GPS. It is my understanding that GPS is very accurate in the x
and y dimensions (lateral measurements), but it really sucks when measuring the
z direction (elevation) since it can't process the signals of satellites on the
other side of the earth (this would be geometrically necessary to get an
accurate measurement of elevation). The result is elevations that are accurate
to scores of feet, not within 6 inches or whatever they claim they measured it
to.

I've not seen this point mentioned here and I'm skeptical about the tracks'
elevations being truly accurate. Not that it really matters. This "GPS
measured tracks" business is mostly just a gee-whiz marketing thing they can put
on the box and website IMO.

--

The Scripps Research Institute
http://www.scripps.edu/~jsmith

by **John Brown** » Thu, 13 Nov 1997 04:00:00

Hello Folks,

GPS is widely used for highly detailed surveying and mapping applications.
Typical accuracy is sub-1m. This is not the same GPS popular on aircraft and
boats, which (even in normal differential GPS mode) has a significantly
lower accuracy. These systems require local differential towers to be
installed and a typical receiver can cost $10,000. For more information,
point your browser to http://www.geowarehouse.com

--
Cheers,
John Browne
CART Team

>as a profession pilot who uses GPS ever day i can confirm that GPS is very
>inaccurate in a vertical realm, often off by 100-150+ feet plus. the
>horizontal position is only accurate to within 40-50+ feet too. with a
>military unscrambled GPS you get 75+ for vertical, and 25+ for horizontal.
>with a new upcoming technology called differential GPS you get 10+ feet
>vertical, 2+ with horizontal BUT you have to know this technology requires
>special towers placed around the countryside, something not yet in place
but
>at small test airports.

>needless to say any GPS survey will pale next to a normal site survey with
>optical equipment. this isn't to say GPS isn't a dream for us pilots.

>David Corsi - Certified Flight Instructor, Commercial Pilot

>PS: GPS in cars work because the GPS "guesses" which road your on by moving
>your horizontal position onto the nearest road in the database. that is why
>it doesn't look like your driving on the sidewalk or something even though
>the actual GPS position may place you there.

by **Jarrod A. Smit** » Thu, 13 Nov 1997 04:00:00

> On Tue, 11 Nov 1997 15:07:50 -0600, "David O. Corsi"

> >as a profession pilot who uses GPS ever day i can confirm that GPS is very
> >inaccurate in a vertical realm, often off by 100-150+ feet plus. the
> >horizontal position is only accurate to within 40-50+ feet too. with a
> >military unscrambled GPS you get 75+ for vertical, and 25+ for horizontal.
> >with a new upcoming technology called differential GPS you get 10+ feet
> >vertical, 2+ with horizontal BUT you have to know this technology requires
> >special towers placed around the countryside, something not yet in place but
> >at small test airports.

> What really matters here are the relative measurements between local
> points x,y,z on the track, not the world-coordinates of those points.
> I.e., you don't care if you can't tell if you are at 100 feet or 250
> feet absolute altitude above sea level- you only care about how much
> higher point A is than point B on the track; and if may be possible to
> calibrate your GPS measurements accordingly. It certainly is easy
> enough to do with an altimeter...

Yeah, but this is different than an altimeter. I mean that as you watch the
measurements being taken in real time, the number that GPS gives you for
elevation can fluctuate while you are _standing still_ by several tens of feet.
It's not like an altimeter where there is just the matter of calibrating it and
then reading off differences in altitude.

--

The Scripps Research Institute
http://www.scripps.edu/~jsmith

rec.autos.simulators

CPR Graphics Too Flat

CPR Graphics Too Flat

CPR Graphics Too Flat

CPR Graphics Too Flat

CPR Graphics Too Flat