[Mapserver-users] Gdaladdo

[Omry Yadan]

Frank,
By high zoom I meant zoomed in.
For zoom out, the performance is relatively alright, but some times I get
very poor time for zoom in.
I think it's a specific zoom that cause me the problems...
Maybe the zoom where I get the image around the real maximum resolution,
with little scaling.
Does it make sense?


-----Original Message-----
From: Frank Warmerdam [mailto:warmerdam at pobox.com] 
Sent: Tuesday, October 21, 2003 5:08 PM
To: Omry Yadan
Cc: mapserver-users at lists.gis.umn.edu
Subject: Re: [Mapserver-users] Gdaladdo

Omry Yadan wrote:
> As I suspected...
> I did not properly benchmark MapServer yet, but I noticed that sometimes
> image generation takes much more time for images in high 'zoom'.
> As long as 8-9 seconds some times, compared to 1-1.5 second for other
maps..
> Why do you think that is? Any suggestions how to improve it?

Omry,

There are many factors that could account for that.  I assume by "high zoom"
you mean "zoomed out", is that right?  Is this primarily working with ECW
rasters?

Even though the ECW technology supports efficient extraction of reduced
resolution images, I don't think that the GDAL ECW driver takes proper
advantage of this capability.  I imagine that is why overview generation
is relatively slow.

If server disk space isn't a big issues I would suggest converting the
ecw files to GeoTIFF and building overviews.  Alternatively we could look
at improving the ECW driver in GDAL to be optimized for MapServer use, but
I don't have the time or unfunded inclination to work on that at this time.

Best regards,

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