Hi,
Oh yes, my images are always covering full mapsheets which are rectangles.
They are naturally polygons, even simple sort of, but in your case you should
use more accurate methods for finding out which images from the 2 m tileindex
file could be removed. Idea remains the same, if you know beforehand that some
images will be left under another image layer you can remove them from the
tileindex so they are not wasting Mapserver processing time. And the goal is
to have only 2 layers:
2m data shows between scale 200k to 100k
2 m data + 20 cm data combined and unnecessary 2 m images removed show between
100k and 500.
Or then you can use just the second layer as "best available image".
Same tileindex file can contain images of both resolution, and in places where
images are overlapping the one which has bigger fid (feature id) in the
shapefile will be drawn last.
-Jukka-
________________________________
Lähettäjä: Liang Jian [mailto:[email protected]]
Lähetetty: 16. marraskuuta 2009 15:40
Vastaanottaja: Rahkonen Jukka; [email protected]
Aihe: RE: [mapserver-users] performance problem with ortho images
Hi Jukka,
I'm not sure that I understand you correctly. I tried to clip 2m data
coverage by 20cm data- get some holes in 2m data index file. And mapfile setup
as follow:
2m data shows between scale 200k to 100k
2m data with holes show between 100k to 500
20cm data shows between 100k to 500.
It doesn't help. I don't think mapserver can read polygons for
tileindex. It sounds like using rectangle.
/Liang
________________________________
From: Rahkonen Jukka [mailto:[email protected]]
Sent: den 16 november 2009 13:36
To: Liang Jian; [email protected]
Subject: Re: [mapserver-users] performance problem with ortho images
Hi,
Is it necessary to show 2 m data at all in the areas where 20-50 cm
imagery is available? If not you can first make tileindex shapefiles from 2 m
images and 20-50 cm images. Open both shapefiles with for example OpenJUMP and
select and remove those polygons from 2 m shapefiles which are totally covered
by you 20-50 cm tiles. Combine the two layer, save and use the result as a
tileindex file for Mapserver.
There may be problems in the areas with overlapping images. To get the
desired image to show on top it may be necessary to rewrite the shapefile by so
that it will be ordered so that the small pixel size images will be written
last in the shapefile. Then they should be drawn on top of 2 m imagery.
If you want the show 2 m images for the whole area when zoomed far
away, prepare still the combined shapefile with covered by -images removed.
Then make two scale dependent layers under the same group. Read 2 m data when
scale is between 200k and 100k and switch then to the combined layer.
There may be better ways, this is the best I have invented this far for
our own use.
Take care of creating enough many low-resolution layers with gdaladdo
for far away zooms. Even then if Mapserver must open more than 20-40 image
files for filling the screen I would consider making a separate overview image
by mosaicing the whole area together with something like 20-50-100 meter pixel
size and using that image in the same image group.
-Jukka Rahkonen-
________________________________
Lähettäjä: [email protected]
[mailto:[email protected]] Puolesta Liang Jian
Lähetetty: 16. marraskuuta 2009 13:02
Vastaanottaja: [email protected]
Aihe: [mapserver-users] performance problem with ortho images
Hi all,
I have a problem with mapserver handling ortho images. The
situation is we have 2m data cover the whole country and 20-50cm data cover
most cities. We setup mapfiles as 2m data shows between scale 200k to 500 and
20-50cm data show between scale 100k to 500. Problem is when requirst data in
the city ranges, mapserver first read data from 20-50cm dataset and then read
from 2m dataset which is unnecessary as the 20-50cm data is enough and the best
solution is when there is no 20-50cm data, 2m data should be used instead.
Do you have any idea how to avoid the unnecessary reading?
Any suggestions will be welcome!
Thanks
/Liang
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