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Re: [Paparazzi-devel] Altitude unit in different messages


From: Felix Ruess
Subject: Re: [Paparazzi-devel] Altitude unit in different messages
Date: Mon, 25 Jun 2012 15:52:15 +0200

Hi Henri,

Thanks to Stephen Dwyer's efforts we could get rid of the initialization hack in NPS. (Due to ground interaction issues it had to be initialized in the air so there was a hardcoded fake hover for initialization).
The jsbsim timestep is now automatically decreased if you are close to the ground which solves the issue of totally crazy values on the ground (also no more bounces).
See https://github.com/paparazzi/paparazzi/pull/222

This and the wp altitude fix is all merged into the release preparation branch v3.9 as well as master...
I would recommend to update/pull in the latest v3.9

Cheers, Felix

On Mon, Jun 25, 2012 at 3:45 PM, Henri Pierre <address@hidden> wrote:
Hi Felix,

That's really cool. I'll have a look to that fix and keep you updated.

Regards
Henri


2012/6/22 Felix Ruess <address@hidden>
Hi again,

I guess you are using NPS, since I found a bug there, is fixed in https://github.com/paparazzi/paparazzi/commit/e84cabf85ab2e0bce19813e6b02f5db14ba9b97f

Cheers, Felix


On Fri, Jun 22, 2012 at 12:42 AM, Felix Ruess <address@hidden> wrote:
Hi Henri,

which simulator? The fixedwing jsbsim one or NPS for rotorcrafts?

Cheers, Felix


On Wed, Jun 20, 2012 at 12:09 PM, Henri Pierre <address@hidden> wrote:
Hi Felix

Ok, so we agree about the difference between altitude in hmsl and altitude in a local frame.

My second question was about an issue I'm facing :
I'm using jsbsim in San Francisco airport which is at sea level. While sending a "MOVE_WAYPOINT x y 50"
message, I receive from server a "WAYPOINT_MOVED x y 4.875853". Try other values, the altitude I get on WAYPOINT_MOVED
is always more or less 10 times less than what I sent...

Example :
MOVE_WAYPOINT 2 2 37.6152257511 -122.356442213 150   ->  WAYPOINT_MOVED 2 2 37.615224 -122.356438 14.875854

Any idea ?

Henri



2012/6/19 Felix Ruess <address@hidden>
Hi Henri,

- The difference beetween altitude in hmsl and altitude in a local frame should be more or less
constant. Right ?

Depends what you mean by more or less... first off the local reference frame is only valid once it has been initalized. The local reference frame can also be reset e.g. via flighplan Geo init block or by calling NavSetGroundReference directly.
Also keep in mind that the local coordinate system is a flat (LocalTangentPlane) system: so the further you go away the bigger your altitude difference will be (the earth and hence hmsl is not flat ;-)

 
- WAYPOINT_MOVED message seems to be the corresponding "echo" of the MOVE_WAYPOINT message. x, y are
longitude and latitude (as in MOVE_WAYPOINT) but altitude seems not to be in hmsl but in local frame ? RIght ?

As I posted previously the WAYPOINT_MOVED and MOVE_WAYPOINT have geodetic coordinates (lat/long/hmsl).
There are no x,y fields, but lat/long... see conf/messages.xml
 
- Is there a way to know which coordinate system is used on each message param ?

Should be mostly obvious from the field names of the message definitions as said above:
WAYPOINT_MOVED, MOVE_WAYPOINT: gedetic
WP_MOVED_ENU: local tangent plane in EastNorthUp
WP_MOVED: UTM coordinates

Cheers, Felix

 
2012/6/13 Felix Ruess <address@hidden>
Hi Henri,

it's not the unit, but the coordinate system that is different.
Also there are always different possible altitude definitions.
See http://paparazzi.enac.fr/wiki/Altitude_definitions

MOVE_WAYPOINT has the position in (geodetic) lat/lon and altitude in hmsl (height above geoid).

WP_MOVED_ENU has the position in a local EastNorthUp frame.
This local tangent plane coordinate system is usually initialized to have it's origin at the vehicle position at startup.
The INS_REF message contains the origin of this reference frame.

Cheers, Felix

On Wed, Jun 13, 2012 at 3:18 PM, Henri Pierre <address@hidden> wrote:
Hello

I face the following issue on the altitude unit :

I send a
Gcs MOVE_WAYPOINT 2 3 37.6148529053 -122.356140137 50    (as describe in message.xml, the altitude is 50 meters)

Server send to uav
SIM_NPS sent  '2 WP_MOVED_ENU 3 17338 37381 1259   ( altitude is 1259 * 0.0039063 = 4.918)

which is 10 times less than what I sent.

Is there a bug or did i do something wrong ?


Regards
Henri

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