[Talk-ca] Map Error

Bégin, Daniel Daniel.Begin at RNCan-NRCan.gc.ca
Mon Oct 25 13:48:06 BST 2010


Hi all,

I would agree with Gordon, it looks pretty much like an artifact left over after the NAD27->NAD83 conversion. These artifacts were corrected when the map were digitized but obviously not in this case.  

Sam, this does not happen across the country along the NTS border lines.  You find edge match problems due to differences in time of aerial photography, aerial photography interpretation, and so on, but not the NAD27->NAD83 conversion.

About GeoBase NHN data, it should be the same because, as explained before, they all come from the same source.


However, the QC team is already having a look and I will get back to you soon.
Thanks,

Daniel




-----Original Message-----
From: talk-ca-bounces at openstreetmap.org [mailto:talk-ca-bounces at openstreetmap.org] On Behalf Of Sam Vekemans
Sent: October 25, 2010 00:40
To: gordon at pinetree.org; Bob Dustan
Cc: talk-ca
Subject: Re: [Talk-ca] Map Error

Hi,
Yes.  Thats most likely correct.  This happens across the country along the NTS border lines.
You might want to check the GeoBaseNHN data, as it could be better.
(since its organized in water basins)[1]

Then we can go 1 level deeper, into the Land Information Ontario
dataset.   A WMS layer is available [2] as well as the source shp
files.  (I do have direct access to it (via a data warehouse loginID)

[1]
wms layer for JOSM  (found on this page
http://wiki.openstreetmap.org/wiki/Geobase/NHN_-_OSM_Map_Feature)
http://wms.cits.rncan.gc.ca/cgi/wms_en.cgi?map=/export/wms/mapfiles/rhn/geobase_rhn.map&version=1.1.1&service=WMS&request=Getmap&layer=HYDRO_AGGREGAT&format=image/png&STYLE=default&layers=GEOBASE_RHN_NHN&

[2]  http://wiki.openstreetmap.org/wiki/Land_Information_Ontario#Data_Access_-_WMS_Layers
You'll have to dig... i'm not exactly sure where the river WMS is..
but i do remember seeing it.  The Ontario servers are considerably slower than NRCan, so you'll need to be patient :)

You might want to try using  Merkaartor, as it can handle WMS layers alot better.
http://wiki.openstreetmap.org/wiki/Merkaartor

Cheers,
Sam

P.S.   great to hear from another Ibycus Topo user :)   One of my
projects is to make a better version of it, now that more data is
available.   I don't know if Dale Atkin is planning on doing the same
at some point.


---
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On Sun, Oct 24, 2010 at 2:16 PM, Gordon Dewis <gordon at pinetree.org> wrote:
> Interesting. I wonder if it's an artefact left over after the NAD27->NAD83 conversion.
>
>  --Gordon
> -----Original Message-----
> From: Bob Dustan <bob.dustan at gmail.com>
> Sender: talk-ca-bounces at openstreetmap.org
> Date: Sun, 24 Oct 2010 14:30:45
> To: talk-ca<talk-ca at openstreetmap.org>
> Subject: [Talk-ca] Map Error
>
> Hi,
>
> I was importing CanVec data for 031E07 and noticed what appears to be 
> an error in the map.  A section of the Oxtongue River seems to be 
> repeated nearby in 031E06.  In OSM you can see it at:
>
> http://www.openstreetmap.org/?mlat=45.317&mlon=-79.0&zoom=15&layers=M
>
> If you use JOSM or Merkaator to view this area and enable the NRCan 
> WMS, you'll see that the error is also in the WMS version of the map.
>
> The error also appears in "The Atlas of Canada" (Toporama) web site at:
>
> http://atlas.nrcan.gc.ca/site/english/maps/topo/map?layers=nodata_ntdb
> _50k%20north_arrow%20other_features%20million_grid%20t50k_grid%20grid_
> 50k_3%20roads%20hydrography%20boundary%20builtup%20vegetation%20popula
> ted_places%20railway%20power_network%20manmade_features%20designated_a
> reas%20water_features%20water_saturated_soils%20relief%20contours%20to
> ponymy%20contour&scale=1400000.000000&mapxy=1281552.5697346777%20-2736
> 73.4692181579&map_layer[northarrow]_class[0]_style[0]=ANGLE%20-14.5876
> 61326428645&mapsize=750%20666&urlappend=
>
> The error also appears in the Ibycus map.
>
> Also, if you look north along the boundary between these 2 map 
> sections, you will see other discrepancies.
>
> I have topo maps of the area that I bought at least 10 years ago.  
> They appear to be scans of paper maps.  When I line up the 2 map 
> sections, everything lines up (roads, rivers, elevation lines, etc.).
>
> It seems to me that some errors (albeit fairly minor) were introduced 
> in the digital form of the map.  Then the errors were propagated to CanVec.
>
> Is there a way to get the map corrected?
>
> Bob
>
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