Re: [Talk-ca] GPS inaccuracy

[Pierre Béland]

Tom

Here is  an initialization procedure to assure you will diminush the inaccuracy 
of measurement by your GPS.  Before starting to record, you open your GPS, 
place it on a spot without moving it for at least five minutes. This will give 
time to the GPS to communicate with various satellites and better estimate your 
position.  After this, the Satellite page should report a precision around 
three meters. But as Daniel said before, this is theoric and not what you will 
obtain.


 
Pierre 



>
> De : Tom Taylor 
>À : "Connors, Bernie (SNB)" ; 
>"talk-ca@openstreetmap.org"  
>Envoyé le : Lundi 19 novembre 2012 10h29
>Objet : Re: [Talk-ca] GPS inaccuracy
> 
>I will do a resurvey in the way you suggest. It was really disappointing to 
>find I couldn't trust my GPS at all (well, I did some mental adjustment of 
>waypoints to place building entrances), and being off by a constant amount for 
>4 km certainly makes one suspicious.
>
>A bit to the north, my GPS survey of some footpaths behind a school matched 
>Bing nicely. It would be really interesting to find some sort of disconnect in 
>between.
>
>Je manquais de la courtoisie envers les francophones qui suivent cette liste. 
>En sommaire, j'ai tracé une piste de longueur totale environ 4 km, mais l'a 
>trouvé toujours environ 10 metres à l'ouest des entités déja presents sur la 
>carte et les images Bing. Je vais faire un autre sondage pour mieux comprendre 
>la situation.
>
>Tom Taylor
>
>On 19/11/2012 8:37 AM, Connors, Bernie (SNB) wrote:
>> Tom,
>> 
>> The transmission lines would not affect your GPS accuracy.  I agree
>> with Pierre that you could repeat the track and see if the two tracks
>> are similar.  Another thing you could do is identify several
>> identifiable points in the Bing Imagery such as the intersection of
>> two sidewalks, the corner of a sports field, etc.  Go to those points
>> and use your GPS to record a waypoint and use position averaging with
>> about 3 minutes of recording to get a more accurate location and then
>> compare those waypoints to the Bing imagery.  Position the Bing
>> imagery so they match up with your waypoints and then look at your
>> GPS tracks top see how they line up with the Bing Imagery.
>> 
>> Bernie. -- Bernie Connors, P.Eng Land Information Infrastructure
>> Unit, SNB bernie.conn...@snb.ca
>> 
>...
>
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Re: [Talk-ca] GPS inaccuracy

[Richard Weait]

On Sun, Nov 18, 2012 at 10:43 AM, Tom Taylor  wrote:
> I had a frustrating experience last night, sorting out an area in my
> neighbourhood. I laid down a GPS track totalling some 4 km. The whole track
> was about 10 meters to the west of the Bing and Canvec data already in
> place. North-south accuracy varied, but wasn't anywhere near so bad.
>
> It doesn't seem worth uploading my track, though maybe I should investigate
> some more.

"Chin up, Buttercup!"  :-)

Don't be frustrated by that result.  EVERY source we use for mapping
will "lie" to us in one way or another.  Our GPSes will vary due to
atmospheric conditions, local interference or reflections, satellite
positions (yes, really), placement of the GPS device in your car or
backpack, etc.

Aerial imagery can be offset, badly referenced, out of date, distorted, etc.

External digital sources can be offset, badly referenced, out of date,
simplified counter to our requirements, just dead wrong, etc.

Our own survey observations can suffer from typo / spell-o errors,
poor handwriting (my fav. :- ) ), mapper distraction / confusion, etc.
 Our own survey photos can suffer from limited resolution,
under-/over-exposure, insufficient contrast, badly-timed truck
blocking the address, etc.

But.  Even with all of those errors we can consider all of our
available sources and improve the map.  Learning the limitations and
error modes of your GPS will only help your mapping over time.  Grab
another similar trace on another day and compare them.  It's fun.

Happy mapping,
Richard

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Re: [Talk-ca] GPS inaccuracy

[Connors, Bernie (SNB)]

Different models of GPSr have different types of antennas.  The two most common 
types that I am aware of are:

1. Patch antenna (e.g. Garmin eTrex models).  The patch antenna in the eTrex 
models gets its best reception when the LCD screen is parallel to the ground.

2. Quadrifilar antenna or Quad Helix antenna (e.g. Garmin 62 models).  The 
Quadrifilar antenna in the 62 models gets its best reception when the LCD 
screen is perpendicular to the ground.

If you have a GPSr you can easily test which type of antenna you have.  Go 
outside and turn on your device and then display the satellite page that shows 
the bar graph of the signal strength for each satellite that is being tracked.  
Wait until you are tracking several satellites.  Now move your GPSr from a 
horizontal position to a vertical position and watch what happens to the bar 
graph.  In testing I did between 2003 and 2007 it was quite easy to see the 
bars shrink or grow depending on which way you held your GPSr.

In a smart phone the GPSr may share an antenna with the cellular radio or 
Bluetooth radio.  The antenna design is most likely NOT optimized for GPS 
reception.  In other words you should not expect the GPSr in a smartphone to 
perform as well as a dedicated GPSr device.

Bernie.
--
Bernie Connors, P.Eng
Land Information Infrastructure Unit, SNB
bernie.conn...@snb.ca



-Original Message-
From: Harald Kliems [mailto:kli...@gmail.com] 
Sent: Monday, 2012-11-19 11:44
To: Tom Taylor
Cc: Connors, Bernie (SNB); talk-ca@openstreetmap.org
Subject: Re: [Talk-ca] GPS inaccuracy

Other things you could do: check if the Canvec data has been moved after being 
imported. As I've said, Bing imagery can be improperly aligned, but not 
everybody is aware of that. So it's possible that a well-meaning mapper has 
moved the Canvec data to match the imagery.
Did you check your GPS devices accuracy reading? While they shouldn't be taken 
too literally, they do give some indication of what's going on (IIRC Garmin 
devices unfortunately do not write the accuracy reading into the GPX file). You 
could also try to improve result by making sure the GPS is in an ideal 
position: This usually means:
device parallel to the ground, with as little obstruction of the upward line of 
sight. Putting it on top of a backpack or your handlebar bag if you're riding a 
bike works best.

 Harald (who tends to get pretty good data with his Etrex Vista Hcx but not so 
much with his smartphone)

On Mon, Nov 19, 2012 at 10:29 AM, Tom Taylor  wrote:
> I will do a resurvey in the way you suggest. It was really 
> disappointing to find I couldn't trust my GPS at all (well, I did some 
> mental adjustment of waypoints to place building entrances), and being 
> off by a constant amount for 4 km certainly makes one suspicious.
>
> A bit to the north, my GPS survey of some footpaths behind a school 
> matched Bing nicely. It would be really interesting to find some sort 
> of disconnect in between.
>
> Je manquais de la courtoisie envers les francophones qui suivent cette 
> liste. En sommaire, j'ai tracé une piste de longueur totale environ 4 
> km, mais l'a trouvé toujours environ 10 metres à l'ouest des entités 
> déja presents sur la carte et les images Bing. Je vais faire un autre 
> sondage pour mieux comprendre la situation.
>
> Tom Taylor
>
> On 19/11/2012 8:37 AM, Connors, Bernie (SNB) wrote:
>>
>> Tom,
>>
>> The transmission lines would not affect your GPS accuracy.  I agree 
>> with Pierre that you could repeat the track and see if the two tracks 
>> are similar.  Another thing you could do is identify several 
>> identifiable points in the Bing Imagery such as the intersection of 
>> two sidewalks, the corner of a sports field, etc.  Go to those points 
>> and use your GPS to record a waypoint and use position averaging with 
>> about 3 minutes of recording to get a more accurate location and then 
>> compare those waypoints to the Bing imagery.  Position the Bing 
>> imagery so they match up with your waypoints and then look at your 
>> GPS tracks top see how they line up with the Bing Imagery.
>>
>> Bernie. -- Bernie Connors, P.Eng Land Information Infrastructure 
>> Unit, SNB bernie.conn...@snb.ca
>>
> ...
>
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Re: [Talk-ca] GPS inaccuracy

[Brent Fraser]

Tom,
Your results are not unusual.  A newer handheld navigation-grade 
receiver has an accuracy of 3 to 5 meters at best (older ones without 
WAAS have an accuracy of 10 m).  Slowly changing (over hours) 
atmospheric effects can introduce an systematic offset into your 
coordinates of 3 to 5 or even 10 meters.


And as others have pointed out, the positional [in]accuracy of Bing and 
Canvec could exceed 10 meters.


Best Regards,
Brent Fraser

On 11/19/2012 8:29 AM, Tom Taylor wrote:
I will do a resurvey in the way you suggest. It was really 
disappointing to find I couldn't trust my GPS at all (well, I did some 
mental adjustment of waypoints to place building entrances), and being 
off by a constant amount for 4 km certainly makes one suspicious.


A bit to the north, my GPS survey of some footpaths behind a school 
matched Bing nicely. It would be really interesting to find some sort 
of disconnect in between.


Je manquais de la courtoisie envers les francophones qui suivent cette 
liste. En sommaire, j'ai tracé une piste de longueur totale environ 4 
km, mais l'a trouvé toujours environ 10 metres à l'ouest des entités 
déja presents sur la carte et les images Bing. Je vais faire un autre 
sondage pour mieux comprendre la situation.


Tom Taylor

On 19/11/2012 8:37 AM, Connors, Bernie (SNB) wrote:

Tom,

The transmission lines would not affect your GPS accuracy.  I agree
with Pierre that you could repeat the track and see if the two tracks
are similar.  Another thing you could do is identify several
identifiable points in the Bing Imagery such as the intersection of
two sidewalks, the corner of a sports field, etc.  Go to those points
and use your GPS to record a waypoint and use position averaging with
about 3 minutes of recording to get a more accurate location and then
compare those waypoints to the Bing imagery.  Position the Bing
imagery so they match up with your waypoints and then look at your
GPS tracks top see how they line up with the Bing Imagery.

Bernie. -- Bernie Connors, P.Eng Land Information Infrastructure
Unit, SNB bernie.conn...@snb.ca


...

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Re: [Talk-ca] GPS inaccuracy

[Harald Kliems]

Other things you could do: check if the Canvec data has been moved
after being imported. As I've said, Bing imagery can be improperly
aligned, but not everybody is aware of that. So it's possible that a
well-meaning mapper has moved the Canvec data to match the imagery.
Did you check your GPS devices accuracy reading? While they shouldn't
be taken too literally, they do give some indication of what's going
on (IIRC Garmin devices unfortunately do not write the accuracy
reading into the GPX file). You could also try to improve result by
making sure the GPS is in an ideal position: This usually means:
device parallel to the ground, with as little obstruction of the
upward line of sight. Putting it on top of a backpack or your
handlebar bag if you're riding a bike works best.

 Harald (who tends to get pretty good data with his Etrex Vista Hcx
but not so much with his smartphone)

On Mon, Nov 19, 2012 at 10:29 AM, Tom Taylor  wrote:
> I will do a resurvey in the way you suggest. It was really disappointing to
> find I couldn't trust my GPS at all (well, I did some mental adjustment of
> waypoints to place building entrances), and being off by a constant amount
> for 4 km certainly makes one suspicious.
>
> A bit to the north, my GPS survey of some footpaths behind a school matched
> Bing nicely. It would be really interesting to find some sort of disconnect
> in between.
>
> Je manquais de la courtoisie envers les francophones qui suivent cette
> liste. En sommaire, j'ai tracé une piste de longueur totale environ 4 km,
> mais l'a trouvé toujours environ 10 metres à l'ouest des entités déja
> presents sur la carte et les images Bing. Je vais faire un autre sondage
> pour mieux comprendre la situation.
>
> Tom Taylor
>
> On 19/11/2012 8:37 AM, Connors, Bernie (SNB) wrote:
>>
>> Tom,
>>
>> The transmission lines would not affect your GPS accuracy.  I agree
>> with Pierre that you could repeat the track and see if the two tracks
>> are similar.  Another thing you could do is identify several
>> identifiable points in the Bing Imagery such as the intersection of
>> two sidewalks, the corner of a sports field, etc.  Go to those points
>> and use your GPS to record a waypoint and use position averaging with
>> about 3 minutes of recording to get a more accurate location and then
>> compare those waypoints to the Bing imagery.  Position the Bing
>> imagery so they match up with your waypoints and then look at your
>> GPS tracks top see how they line up with the Bing Imagery.
>>
>> Bernie. -- Bernie Connors, P.Eng Land Information Infrastructure
>> Unit, SNB bernie.conn...@snb.ca
>>
> ...
>
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Re: [Talk-ca] GPS inaccuracy

[Tom Taylor]

I will do a resurvey in the way you suggest. It was really disappointing 
to find I couldn't trust my GPS at all (well, I did some mental 
adjustment of waypoints to place building entrances), and being off by a 
constant amount for 4 km certainly makes one suspicious.


A bit to the north, my GPS survey of some footpaths behind a school 
matched Bing nicely. It would be really interesting to find some sort of 
disconnect in between.


Je manquais de la courtoisie envers les francophones qui suivent cette 
liste. En sommaire, j'ai tracé une piste de longueur totale environ 4 
km, mais l'a trouvé toujours environ 10 metres à l'ouest des entités 
déja presents sur la carte et les images Bing. Je vais faire un autre 
sondage pour mieux comprendre la situation.


Tom Taylor

On 19/11/2012 8:37 AM, Connors, Bernie (SNB) wrote:

Tom,

The transmission lines would not affect your GPS accuracy.  I agree
with Pierre that you could repeat the track and see if the two tracks
are similar.  Another thing you could do is identify several
identifiable points in the Bing Imagery such as the intersection of
two sidewalks, the corner of a sports field, etc.  Go to those points
and use your GPS to record a waypoint and use position averaging with
about 3 minutes of recording to get a more accurate location and then
compare those waypoints to the Bing imagery.  Position the Bing
imagery so they match up with your waypoints and then look at your
GPS tracks top see how they line up with the Bing Imagery.

Bernie. -- Bernie Connors, P.Eng Land Information Infrastructure
Unit, SNB bernie.conn...@snb.ca


...

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Re: [Talk-ca] Import des limites administratives, municipalités du Québec

[Fabian Rodriguez]

-BEGIN PGP SIGNED MESSAGE-
Hash: SHA1

On 12-11-18 10:08 PM, Pierre Béland wrote:
> Merci Dega.
>
> J'ai effectivement l'intention de rejoindre les contributeurs via
l'historique et l'identifiant de chacun.
N'oubliez pas de les inviter à s'inscrire à cette liste, et à se rendre
visibles sur:
http://wiki.openstreetmap.org/wiki/Category:Users_in_Quebec
[...]
> Les sites qui traitent de données libres entretiennent également cette 
> confusion. Ils n'informent
pas adéquatement sur la portée des licences actuelles. Par exemple, le
site http://capitaleouverte.org/ fait la promotion des données libres et
présente la licence PPDL. Celle-ci est vraiment une licence de données
libres. En contradiciton avec ces principes, on vent en première page la
publication de données par la ville de Québec, sans nuances, sans
indiquer les restrictions contenues dans la licence. On mentionne un
groupe de villes qui ont toutes des licences avec restrictions :
> Québec avait un retard, elle est maintenant «à la page» en rejoignant,
entre autres, Ottawa, Edmonton et Montréal, qui publient aussi des
données ouvertes.
>

Je serais intéressé à corriger le tir et informer les intéressés à ce sujet.

Est-ce qu'on pourrait consolider l'information que tu as sur ces
restrictions pour les présenter de manière cohérente et claire?

F.


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Re: [Talk-ca] GPS inaccuracy

[Gregory]

Who said Bing and/or Canvec are accurate?


On 18 November 2012 19:31, Tom Taylor  wrote:

> Mostly the buildings were two stories only. A high-voltage transmission
> line runs behind them, the width of the buildings and more away, but maybe
> it had some effect.
>
>
> On 18/11/2012 11:23 AM, Pierre Béland wrote:
>
>> Tom
>>
>> You can try to repeat the experience with this same GPS and compare your
>> results.
>>
>> I dont know if this is the case for your. In urban areas, the tall
>> buildings are obstacles to Satellilte signal. This increases the inaccuracy
>> of GPS measurement. If you are close to a tall building, you wont receive a
>> good signal from that direction. Your position is calculated with a
>> principle of triangulation. You
>> need to receive the signal fo at least three satellites. And results are
>>   far better with four.
>>
>>
>>
>> Pierre
>>
>>  ...
>
>
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o...@livingwithdragons.com
http://www.livingwithdragons.com
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Re: [Talk-ca] Import des limites administratives, municipalités du Québec

[Pierre Béland]

Bruno,

C'est effectivement le chemin du combattant.  

Si nous obtenons le droit de publier avec licence ODbl, il devrait être 
possible de déposer une copie sur Mapcraft. Quelle est l'utilité de déposer ces 
limites sur Mapcraft?


 
Pierre 



>
> De : Bruno Remy 
>À : Pierre Béland  
>Cc : "talk-ca@openstreetmap.org" ; dega 
> 
>Envoyé le : Dimanche 18 novembre 2012 22h32
>Objet : Re: [Talk-ca] Import des limites administratives, municipalités du 
>Québec
> 
>
>Merci Pierre, pour ces précisions et informations.
>
>On avance dans le bon sens... même si le chemin est long et difficile.
>Une idée en passant: on pourrait aussi déposer une version "allégée" du 
>fichier OSM lorsqu'il sera terminé (sans les relations, ou bien juste les MRC) 
>sur le site de MapCraft : cela permet un découpage pour un travail 
>collaboratif sur différents projets. Un exemple vaut mille mots ;) 
>:http://mapcraft.nanodesu.ru/pie/109
>
>
>Bruno Remy
>Le 2012-11-18 22:09, "Pierre Béland"  a écrit :
>
>Merci Dega.
>>
>>
>>J'ai effectivement l'intention de rejoindre les contributeurs via 
>>l'historique et l'identifiant de chacun.
>>
>>
>>
>>Tout comme le ministère de la sécurité publique, la SQ doit utiliser les 
>>données produites par le MRNF. C'est le MRNF qui a le copyright.
>>
>>
>>Vendredi, j'ai fait à nouveau une demande au site de données libres du 
>>gouvernement du Québec. Je leur ai demandé de nous donner exceptionnellement 
>>l'autorisation d'importer la Base de données géographiques et administratives 
>>à l’échelle de 1/1 000 000 du MRNF dans la base de données OpenStreetMap et 
>>de les publier souslicence ODbl.
>>
>>
>>L'avantage de ces données, c'est que c'est un jeu cohérent qui comprend 
>>municipalités, territoires non occupés et territoires autochtones et les 
>>codes / MRC et régions administratives. Frank Stegging a déjà converti ce jeu 
>>de données au format OSM. Le fichier OSM comprend également les relations.  
>>Il sera facile ensuite de produire les relations MRC et régions 
>>administratives.
>>
>>
>>Comme le disait Richard Weait récemment, la ville de Vancouver a entrainé les 
>>autres municipalités à la dérive. Tous publient avec ces mêmes licences 
>>restrictives. Les gouvernements et
 municipalités disent vouloir suivre le mouvement OpenData.  On énonce de beaux 
grands principes tels que Transparence, Collaboration, Participation. 
Cependant, on ne donne pas aux citoyens les moyens de réaliser de tels projets.
>>
>>Les sites qui traitent de données libres entretiennent également cette 
>>confusion. Ils n'informent pas adéquatement sur la portée des licences 
>>actuelles. Par exemple, le site http://capitaleouverte.org/ fait la promotion 
>>des données libres et présente la licence PPDL. Celle-ci est vraiment une 
>>licence de données libres. En contradiciton avec ces principes, on vent en 
>>première page la publication de données par la ville de Québec, sans nuances, 
>>sans indiquer les restrictions contenues dans la licence. On mentionne un 
>>groupe de villes qui ont toutes des licences avec restrictions : 
>>
>>Québec avait un retard, elle est maintenant «à la page» en rejoignant, 
entre autres, Ottawa, Edmonton et Montréal, qui publient aussi des 
données ouvertes. 
>>
>>
>>Pierre 
>>
>>
>>
>>>
>>> De : dega 
>>>À : talk-ca@openstreetmap.org 
>>>Envoyé le : Lundi 29 octobre 2012 9h30
>>>Objet : [Talk-ca] Import des limites administratives, municipalités du Québec
>>> 
>>>Le 5 octobre 2012, Pierre Béland a écrit
 C'est
 pourquoi je propose d'arrêter l'import et la modification
 des limites administratives de municipalités, arrondissements, etc.
 et d'en discuter sur cette liste avant de poursuivre le travail.
>>>
 Pour le travail d'import, il me semble souhaitable de centraliser ce 
>>>travail.
 Je suis expérimenté dans le traitement de telles données.
 Si les collaborateurs du Québec sont d'accord, je pourrais  me charger du 
>>>travail d'import. 
>>>
>>>Je suis à l'origine du tracé des limites de La Prairie.
>>>Je l'ai fait, à l'époque (2008), pour expérimenter le logiciel de navigation 
>>>navit. Ma référence était une carte imprimée provenant de la ville.
>>>J'ai aussi utilisé des cartes de la Sûreté du Québec pour tracer les limites 
>>>de St-Faustin-Lac-Carré.
>>>Je n'ai pas de problème à retirer mon tracé pour que tu puisses le remplacer 
>>>par une version plus précise.
>>>
>>>Je propose qu'on en
 fasse une activité de formation. Il faudra clairement 
>>>identifier les balises nécessaires et la façon de créer les relations.
>>>Je crois que tous ceux qui ont créé/édité des limites administratives 
>>>doivent 
>>>en être informés. Mais, à ma connaissance, les contributeurs québécois ne 
>>>lisent pas talk-ca, probablement à cause de son orientation très anglo. Par 
>>>contre, il serait simple d'exporter la liste de tous ces contributeurs de 
>>>limites et de leur envoyer un courriel.
>>>Si tu ne ré