Re: [boost] GIL io_new review

Subject: Re: [boost] GIL io_new review
From: Mateusz Loskot (mateusz_at_[hidden])
Date: 2010-12-09 11:09:47

On 09/12/10 15:16, Domagoj Saric wrote:
> "Mateusz Loskot" <mateusz_at_[hidden]> wrote in message
> news:4D00DA5D.3040400_at_loskot.net...
>> 1. Which raster are we taking from the True Marble Imagery?
>
> The largest one ( TrueMarble.250m. 21600x21600.E2.tif.gz 628MB) ?

Good.

>> 2. To keep things simpler, let's cut the raster to even tiles.
>> For example, tiles of 200x200 pixels
>> This will give us constant number of 11664 tiles for 21600x21600 raster.
>
> OK.

OK.

Though, GDAL itself reports the optimum block size as 512x512, see
last 3 lines:

gdalinfo.exe TrueMarble.250m.21600x21600.E2.tif
Driver: GTiff/GeoTIFF
Files: TrueMarble.250m.21600x21600.E2.tif
Size is 21600, 21600
Coordinate System is:
GEOGCS["WGS 84",
     DATUM["WGS_1984",
         SPHEROID["WGS 84",6378137,298.257223563,
             AUTHORITY["EPSG","7030"]],
         AUTHORITY["EPSG","6326"]],
     PRIMEM["Greenwich",0],
     UNIT["degree",0.0174532925199433],
     AUTHORITY["EPSG","4326"]]
Origin = (0.000000000000000,45.000000000000000)
Pixel Size = (0.002083333333333,-0.002083333333333)
Metadata:
   AREA_OR_POINT=Area
Image Structure Metadata:
   INTERLEAVE=PIXEL
Corner Coordinates:
Upper Left  (   0.0000000,  45.0000000) (  0d 0'0.01"E, 45d 0'0.00"N)
Lower Left  (   0.0000000,   0.0000000) (  0d 0'0.01"E,  0d 0'0.01"N)
Upper Right (  45.0000000,  45.0000000) ( 45d 0'0.00"E, 45d 0'0.00"N)
Lower Right (  45.0000000,   0.0000000) ( 45d 0'0.00"E,  0d 0'0.01"N)
Center      (  22.5000000,  22.5000000) ( 22d30'0.00"E, 22d30'0.00"N)
Band 1 Block=512x512 Type=Byte, ColorInterp=Red
Band 2 Block=512x512 Type=Byte, ColorInterp=Green
Band 3 Block=512x512 Type=Byte, ColorInterp=Blue

It means, size of block for best efficiency of raster I/O operations.
I will test 200x200 and 512x512 if time permits.

>> 4. Cutting TIFF to PNG involves compression. If we are interested in
>> raster access, RIO, I/O speed, perhaps we could stick to TIFF as
>> output format as well. What you think?
>
> That depends on what exactly are we trying to test here, the C++
> wrappers (e.g. io_new vs io2) and/or the backends (e.g. LibTIFF vs WIC)
> and/or something third...

Actually, that was part of my initial question.

> Are you sure the TrueMarble GeoTIFFs are uncompressed?

Yes, these TIFF (GeoTIFF in fact) files are uncompressed.
That's why the TIFF files are provided as .gz files.

The gdalinfo utility output I've provided above also does not display
any compression properties. If the file was compressed, corresponding
key-value would be reported, for example:

Image Structure Metadata:
   COMPRESSION=LZW

Here are details about this metadata:
http://gdal.org/frmt_gtiff.html

Also, Windows Explorer -> file Properties report it's uncompressed.

Best regards,
-- 
Mateusz Loskot, http://mateusz.loskot.net
Charter Member of OSGeo, http://osgeo.org
Member of ACCU, http://accu.org