[mapserver-users] TileIndex - accuracy and truncation ?

[Travis Kirstine]

Could it also be the resampling of the image and or an issue with the PNG
format?  I would try tiled geotiffs.


On Thu, Jun 12, 2014 at 5:47 PM, Lime, Steve D (MNIT) <
Steve.Lime at state.mn.us> wrote:

>  The world files are read internally by GDAL, not MapServer. I wonder if
> there’s a way to test this just using GDAL and take MapServer out of the
> equation completely. Is there any projection being done? That could also be
> a source of slivers. Is it possible to generate the tiles with just a bit
> of overlap?
>
>
>
> Steve
>
>
>
> *From:* mapserver-users-bounces at lists.osgeo.org [mailto:
> mapserver-users-bounces at lists.osgeo.org] *On Behalf Of *Lars I. Nielsen
> *Sent:* Thursday, June 12, 2014 9:02 AM
> *To:* mapserver-users at lists.osgeo.org
> *Subject:* [mapserver-users] TileIndex - accuracy and truncation ?
>
>
>
> Hi,
>
>
>
> For performance reasons, I've (used FME to) split a large PNG into 450
> small tiles, serving them with a Mapserver tileindex as a WMS service to a
> web solution.
>
>
>
> Howeever, white lines appear between some of the tile rows (not all) at
> some scales (not all).
>
>
>
> I've looked deeper into the WLD files for the individual tiles, and found
> that the calculations are accurate to 1/10 of a nanometer. At least if one
> uses all 10 decimals.
>
>
>
> Tiles are 2254 pixels high, and (as per the WLDs below) 6138899.3169212583
> - 0.0204375000 * 2254 = 6138853.2507962583 (almost equal to
> 6138853.2507962584)
>
>
>
> Which leads me to suspect that some sort of truncation goes on, yielding
> some sort of rounding error.
>
>
>
> Do anyone know whether the tileindex calculations truncates any of the
> values in the WLD files ? And if so, by how much ?
>
>
>
> Cheers.
>
>
>
> --
>
>
>
> A typical map picture with a white line can be seen via this link:
>
>
>
>
> http://hvmgo01.hvenegaard.dk/mswms/mapserv.exe?map=odensekkgd_wms.map&LAYERS=ASSISTENS&TRANSPARENT=true&SERVICE=WMS&VERSION=1.1.1&REQUEST=GetMap&STYLES=&FORMAT=image/png&SRS=epsg:25832&BBOX=586609.80952408,6138781.1015875,586686.0222225,6138857.3142859&WIDTH=256&HEIGHT=256
>
> Here's the WLD of the two tiles displayed in the picture:
>
>
>
> Upper tile WLD:
>
> 0.0204375000
>
> 0.0000000000
>
> 0.0000000000
>
> -0.0204375000
>
> 586620.6934394070
>
> 6138899.3169212583
>
>
>
> Lower tile WLD:
>
> 0.0204375000
>
> 0.0000000000
>
> 0.0000000000
>
> -0.0204375000
>
> 586620.6934394070
>
> 6138853.2507962584
>
>
>
> --
>
>
>
> Ps! As I wrote previously, I'm using FME to create the tiles. So I have
> little control over the actual coordinate and pixel values, and only
> specify the number of tiles I need. So manual truncation is not really a
> viable option.
>
>
>
>
>
> Kind regards / Med venlig hilsen
> Lars I. Nielsen
> ----------------------------------------------------------------
>
> Landinspektør, Senior GIS Programmør og Konsulent
> Hvenegaard Landinspektører A/S
> Rugaardsvej 55, DK-5000 Odense C
> Denmark
> Tel. +45 6313 5050
> http://www.hvenegaard.dk
>
>
>
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>



-- 

*Travis Kirstine*
*First Base Solutions I**nc*.
tkirstine at firstbasesolutions.com

140 Renfrew Dr. | Suite 100 | Markham, ON | L3R 6B3
p. 905-477-3600 ext. 301 | m. 647-534-4798
http://www.firstbasesolutions.com
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