[OSM-newbies] projection question in Hawaii

[David Groom]

> ----- Original Message ----- 
> From: "Randy George" <rkgeorge at cadmaps.com>
> To: <newbies at openstreetmap.org>
> Sent: Thursday, April 02, 2009 3:49 PM
> Subject: Re: [OSM-newbies] projection question in Hawaii
>
>
>
> Hi,
>
> Perhaps the island is offset. This test case lets me show OSM over
> VE: http://www.web-demographics.com:8087/ The offset appears consistent
> around the Island. Yahoo and VE align. Also the intersection locations 
> align
> on Google Earth
>
> The cyan tracks in this test are from GPS:
> http://www.web-demographics.com/Exacter/test.html and you can use the 
> infor
> check map click to get the GPS record behind any of the points.
>
> The offset seems consistent around the coast.
> dx= -0.002608
> dy = 0.003020
>
> randy
>

>From when I worked on the improving the coastline data around Hawaii I got 
the impression that the TIGER import was offset from reality.

http://wiki.openstreetmap.org/wiki/TIGER_fixup#Accuracy:_Offset_from_reality

However not being based on HI I had no way of confirming this with actual 
GPS measurements.  Your track data seems to confirm the offset, and I would 
suggest that all data imported from TIGER needs shifting.

I'm not aware of an easy method of achieving this shift however.  A similar 
problem existed on Guam, and I advised that importing the island into JOSM 
and dragging all the data would allow the correction, but I think that for 
HI the size of the data might swamp JOSM.

David

> -----Original Message-----
> From: newbies-bounces at openstreetmap.org
> [mailto:newbies-bounces at openstreetmap.org] On Behalf Of swanilli
> Sent: Wednesday, April 01, 2009 6:49 PM
> To: newbies at openstreetmap.org
> Subject: Re: [OSM-newbies] projection question in Hawaii
>
> Maybe this is evidence of a wider problem with Pacific Islands that
> are close to the International Dateline.
>
> I have noticed that the location for the country tags for both Fiji
> and Tonga are a long way from their true location.
>
> For Fiji the country is located on OSM at
> http://www.openstreetmap.org/?lat=-28.08334&lon=-179.99&zoom=15. This
> is probably a typing error (someone hit tie 2 key instead of 1) and
> probably was meant to be
> http://www.openstreetmap.org/?lat=-18.08334&lon=-179.99&zoom=15 which
> would put it in the middle of the Fiji group of islands).
>
> I would have fixed these errors except that I don't know how to move a
> country.
>
> Any suggestions on how to fix this?
>
>
>
> 2009/4/2 Iván Sánchez Ortega <ivan at sanchezortega.es>:
>> El Miércoles, 1 de Abril de 2009, Randy George escribió:
>>> I also checked against Google Earth by locating LL -155.136552,
> 19.68534
>>> on OSM and on GE. GE shows this point at the road intersection of Akolea
> Rd
>>> and Kaumana Dr, while in OSM it's shifted off the road?
>>>
>>> I assume I am doing something irregular. Are the OSM tiles
>>> sphericalmercator EPSG:900913? Or some other EPSG?
>>
>> Yeah, OSM uses 900913 for rendering. Internally (for editing) it uses
>> unprojected WGS84 (AKA EPSG:4326).
>>
>>
>> Maybe the OSM data for that zone is just wrong (badly surveyed, maybe?)
> and
>> needs to be fixed. Have you checked (with a GPS) that zone?
>>
>>
>> Cheers,
>> --
>> ----------------------------------
>> Iván Sánchez Ortega <ivan at sanchezortega.es>
>>
>> Un ordenador no es un televisor ni un microondas, es una herramienta
> compleja.
>>