The steps you've listed below are correct for maximizing performance when
viewing the raster at (or around) the native resolution of the data. However,
as you've found out, the performance can still be poor when trying to view the
entire dataset.
The basic rule is that your application (mapserver?) should not have to open
more than 4 to 8 raster files to render the view. With that in mind (and since
disk space is not a problem), create "layers" of the raster dataset at different
scales, say a factor of 2, until you have only one image.
For example, if the resolution of your original data is 1 meter per pixel, your
layers would look like the following. Note the first eight layers are handled
by the internal overviews you created with gdaladdo.
Pixel Map Scale:
Size: 1:n
----- ------
1 m 4,000
2 8,000
4 16,000
8 32k
16 64
32 128
64 250
128 500
Additional External Layers
256 1m
512 2m
1024 4m
2048 8m
4096 16m
To create the additional external layers, use GDAL's gdalbuiltvrt to create a
VRT file of the original dataset. You can then use gdal_retile.py or Maptiler
to build the layers.
Best Regards,
Brent Fraser
Edi KARADUMI wrote:
I have read many strategies for raster performance, but i still have
problems with my case. The posts that i have read explain the strategie,
but are not very detailed. Im new to mapserver so i have problems
implementing them. My case is:
-about 6000 tiles that form the map
-170mb each tile
-aproximately 1.2T of iamges
-i have 10T HD and i think disk space is not a problem for me
-tile format is TIF
-tile size 9375x6250 pixels
The strategy i have implemented and the problems i have
-First i divided the tiles in 60 folders, to increase the performance in
disk seek/read.
-Than i transformed source files into internally tiles with the command
gdal_translate -of GTiff -co "TILED=YES" original.tif tiled.tif
-i used gdaladdo to add internal pyramids
gdaladdo -r average 2 4 8 16 32 64 128
-Created a tileindex using
gdaltindex -write_absolute_path MapAll.shp
//server/Maps/Subfolder1/*.tif
-Created a spatial index .qix file
shptree MapAll.shp
-than added the layer to the mapfile without the .shp extension so the
application can use the .qix
as you may know, i have very slow performance when i zoom out and im
stucked here. As i have read i should make a copy of the tiles with
reduced resolution. Merge the tiles together and use min/max scale to
show different layers in different scales. the min/max scales i zoom
in/out are 100/1200000. Now my questions are
- How can i calculate the scale where i should create another layer of
the tiles, or i shoud see it with some tests?
- how much should be the resolution of the new layer?
- is there any tools or program to merge the tiles? merging 6000 tiles
with the gdalwarp by writing the command by myself is frustrating
- how many tiles should i merge together to create the new layer? (how
many tiles should have the new layer) i know that in each zoomscale its
better to appear only one tile but i dont know how to calculate it
- the tiles that i should merge are the originals or those with internal
tiling and overviews?
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