[mapserver-users] preparing orthos for Mapserver?

[Rahkonen Jukka]

Hi,

Have also definitely a try with JPEG compressed tiffs. You can save 90% of the disk space with nominal effect on speed and quality, but that depends on your hardware and imagery.  It is still worth testing. The command to use is 
gdal_translate -of GTiff -co tiled=yes -co compress=JPEG -co photometric=YCBCR 

For overviews use 
gdaladdo -r average -ro --config COMPRESS_OVERVIEW JPEG --config PHOTOMETRIC_OVERVIEW YCBCR 

With or without -ro is a matter of taste. By using internal overviews you will save a bit more space because external overviews have some ballast but if you want to archive images sometimes you can discard the external overviews and save some disk space by that time.

Tiffs are not as hopeless than plain JPEGs of PNGs and images do not need to be read totally into memory. 
Untiled tiffs are usually written in stripes so for reading a box from an arbitrary place inside the image it is enough to read all the scan lines which intersect that box. It is still more data than what is needed with tiled images. 

There are also clever tiff readers which can read fast, let's say, every 10th row and column from uncompressed tiff and create an subsampled, nearest neighbour subsample in-the-fly. I have used one such in the 90's and Intel 386 computers could handle pretty well uncompressed tiffs of size 10000x10000 pizels without overviews. I think that GDAL can't do that kind of selecting and this is more nice-to-know stuff from the stone age. What to remember is that tiles and overviews are essential for GDAL and Mapserver.

-Jukka Rahkonen-
________________________________________
Stephen Woodbridge wrote:

> On 10/4/2013 3:45 PM, Worth Lutz wrote:
>> I have a question on preparing a set of orthophoto tiff files for use
>> with MapServer.
>>
>> The orthophotos are 10,000 x 10,000 pixels with 6 in. resolution.
>>
>> Currently I have a tile index pointing to these files.
>>
>> I’m wondering about internal tiling and overlays. Should I process these
>> tiles with gdal to internally tile each one and add internal overlays.
>>
>> I’m thinking that the overlays would be more useful that the internal
>> tiling based upon the size of the current tiles.

> Yes, you should do both of these. The internal tiling is very important
> when you access a very small part of the image so you do not have to
> pull the whole image into memory just to access a small part of it.

> The overlays are import when you are zooming out so you do not have to
> resample on the fly.

> -Steve W

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