[Talk-GB] OS OpenData StreetView Tiles now available

Oliver O'Brien mail at oliverobrien.co.uk
Wed Apr 7 14:56:01 BST 2010


Just to throw more things into the mix, I have a third set of OS Street View
tiles, only z11-z15 though as my overall method's much slower :-( which was
produced using a different workflow to the first two. I'm using TimSC's
warp-gbos program that was used to rectify the Scottish Popular Edition
maps. This reprojects each source TIFF (and coverts it to JPG), it then
tiles the JPGs, choosing individual pixels where going across source image
boundaries.

I also see the characteristic kinks, but in different places. Mine seem to
be generally *worse* (i.e. do not use mine for tracing!) although this might
also be something to do with JPG compression.

For some z16s I do have, compare:
http://splintmap.geog.ucl.ac.uk/~ollie/osopendata/streetview/16/32760/21780.
jpg
and: 
http://a.os.openstreetmap.org/sv/16/32760/21780.png

It looks like the os.osm set is correcting itself every few metres - hence
those kinks appearing whereas I just have one big, horrible correction,
about 70% down the tile.

By the way you can see my set at:
http://splintmap.geog.ucl.ac.uk/~ollie/osopendata/sv/

One thing I've already noticed, over and above the minor differences between
the 900913 Street View sets, is how dramatically off the NPE maps are in
certain places - GPS traces and OS Street View generally in agreement, while
NPE can be off by ~2-300m. I redid a village last night which had been
clearly traced in NPE - it was not good at all. None of the roads were
connected to the other roads, and the GPS traces that were present for a
couple of the streets were way off. I think the OS Street View-based tracing
is now much closer to the truth.

Ollie

--------------------------------------------

Date: Wed, 7 Apr 2010 13:34:26 +0100
From: Grant Slater <openstreetmap at firefishy.com>
Subject: Re: [Talk-GB] OS OpenData StreetView Tiles now available
To: TimSC <mapping at sheerman-chase.org.uk>
Cc: talk-gb at openstreetmap.org
Message-ID:
	<t2hfd93759a1004070534k83cf578ck1b5cc71be78b531e at mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1

On 7 April 2010 12:53, TimSC <mapping at sheerman-chase.org.uk> wrote:
> In both the edgemaster's and Richard's tiles there are periodic kinks
> (about 1 pixel in size) in what should be straight lines. It is more
> obvious in Richard's tiles because they are less noisy. Any idea what is
> causing that?
>

The warping between OSGB36 (EPSG: 27700) and EPSG: '900913'.

Richard's tiles use a custom conversion script with antialiasing on
the resample. Edgemaster's tile used gdal2tiles.

I'm working on some cleaned up and pngcrush'ed tiles, but do not
expect them in the next few days. The existing tiles are more than
good enough.

/ Grant





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