Chapter 4 in ASDAR book GeoTiff question
On Sat, Jun 29, 2013 at 11:11 PM, Hodgess, Erin <HodgessE at uhd.edu> wrote:
Dear GEO-phytes I am working through the ASDAR book (which is TOTALLY amazing), and I have a question about something in Chapter 4, please: We are looking at a GeoTiff file, and get the following warning message at the end.
GDALinfo("70042108.tif")
rows 1200
columns 1320
bands 1
lower left origin.x 174.2
lower left origin.y -37.5
res.x 0.0008333333
res.y 0.0008333333
ysign -1
oblique.x 0
oblique.y 0
driver GTiff
projection +proj=longlat +datum=WGS84 +no_defs
file 70042108.tif
apparent band summary:
GDType hasNoDataValue NoDataValue blockSize1 blockSize2
1 Float32 FALSE 0 1 1320
apparent band statistics:
Bmin Bmax Bmean Bsd
1 -4294967295 4294967295 NA NA
Metadata:
AREA_OR_POINT=Area
TIFFTAG_RESOLUTIONUNIT=1 (unitless)
TIFFTAG_SOFTWARE=IMAGINE TIFF Support
Copyright 1991 - 1999 by ERDAS, Inc. All Rights Reserved
@(#)$RCSfile: etif.c $ $Revision: 1.11 $ $Date$
TIFFTAG_XRESOLUTION=1
TIFFTAG_YRESOLUTION=1
Warning message:
statistics not supported by this driver
I was wondering about this since GeoTiff is one of the supported drivers.
Some geospatial image formats store 'statistics' of their data in themselves - things like the mean and variance of the data - are kept in little metadata chunks so that software doesn't have to loop over the data and compute it whenever needed. The warning message is just saying that the GeoTiff driver in GDAL doesn't support this kind of metadata. If GDAL has to get say, the mean value of a band, it will have to loop over and compute it rather than just getting the number from the metadata statistics block. Thomas Adams doesn't get this message - either he's got a different version of the GDAL library that does handle statistics metadata, or he's got a different version of sp or rgdal (wherever GDALInfo comes from) that doesn't bother warning you. Either way, it doesn't really matter! Barry