[mapserver-users] How to improve raster imagery display ?

pcreso at pcreso.com pcreso at pcreso.com
Sat Sep 13 20:13:15 EDT 2008


Hi Rainer,

Firstly, are you using FastCGI? If not, implementing this may help. I assume you have indexes to all the raster images.

I'd also consider an architectural approach, where you abstract the raster data to a custom built system & access this via WMS. We have improved performance of such systems by having mapfiles access data from PostGIS databases on disparate servers rather than one congested system.

Similarly, for rasters, you may also be able to use hardware rather than software to address your performance issues by splitting your raster files up between servers, effectively a further level of tiling. With caching (as below), multiple users hitting the same region should generally hit the cache, and users hitting multiple regions will have their load spread across different servers. 

Look at http://geowebcache.org/
While it possibly integrates better with GeoServer than mapserver, it will supposedly work with any WMS server.

Given the cheap price of hardware & memory/cpu performance these days, adding a couple of multi-core boxes with a few GB of memory & a Tb drive or two each isn't a huge outlay, & Gb LAN is also cheap.



I guess when your programming skills are as bad as mine, you look at other solutions first :-)

I'm interested in hearing about your project, we are in the process of accumulating around 11Tb of aerial imagery & will be looking at ways to provide access to this.


Cheers,

  Brent Wood


--- On Sun, 9/14/08, Rainer Kalliany <rainer at kalliany.at> wrote:

> From: Rainer Kalliany <rainer at kalliany.at>
> Subject: [mapserver-users] How to improve raster imagery display ?
> To: mapserver-users at lists.osgeo.org
> Date: Sunday, September 14, 2008, 11:24 AM
> Dear all,
> 
> Yet for some months, my wife (who is the far more
> experienced programmer,
> and me (rather responsible for
> collecting/re-formatting/providing data)
> are developing a MapServer-based webGIS. Your community
> already has
> helped us several times a lot with your experience, and we
> are most
> grateful for that great support.
> 
> Now, with our project almost finished, the so far pretty
> poor performance
> in displaying raster images (aerial orthophotos at a ground
> resolution of
> 0.25 metres) is becoming a critical issue. In particular
> when several
> users want to work at the same time, what happened last
> week :-(
> 
> So far we had our orthophotos organized in a seamless grid
> of ECW-images,
> 10000 by 10000 pixel each (corresponding to 2500 by 2500
> metres on ground).
> 
>  From that dataset our MapServer produces the
> "orthophoto" layer on demand,
> at scales of 1 by 1000, 2000, 5000 or 10000. With the
> standard settings
> of 72 dpI, that renders pixels of 0.353, 0.706, 1.764 or
> 3.528 metres.
> 
> I am well aware that at least for the 10000 scale I should
> introduce
> a layer with reduced resolution. I already have prepared
> such a dataset.
> 
> But our main concern are the scales 2000 and 1000, where
> the displaying
> process is producing many dozens of tiles, each 256 x 256
> pixel .png-files.
> Along with the other layers (where the vector-data also are
> displayed by
> rasterized tiles which at least are much smaller), the
> composition of one
> screen sometimes takes up to 3 minutes !
> 
> NOW MY IDEA is to produce all those .PNGs (with their weird
> directory
> structure and naming, like
> \t-86016\l3072\t-84992l4352.png, which how-
> ever I already have understood) in advance and myself. For
> the conversion
> from ECW to PNG I might use GDAL, but without any
> resampling necessary.
> 
> I also consider raising tilewidth/tileheight from the
> standard value 256
> to 512 or even 1024 pixels.
> 
> Now my question is, if that is a good idea or not.
> 
> If you disagree with me: Do you have some alternative
> proposal ?
> 
> If you think my planned approach basically is a good one,
> do you have
> any supporting advices, on issues I possibly did not
> consider ?
> 
> THis is becoming a dcisive isuue for the success of our
> whole project,
> and therefore we will be most grateful for any hint !
> 
> With kind regards,
> 
> Rainer & Susanne Kalliany
> 
> 2008-09-13, 23:25 UTC
> -- 
> DI. Rainer Kalliany - rainer at kalliany.at
> 
> TeFiS - www.tefis.at
> Technische und forstliche Informationssysteme (Forstliche
> Software, GIS)
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> Ingenieurbüro für Vermessungswesen (Photogrammetrie,
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> 
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> 
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