esri-grid-formatqgis
I have been trying to open Esri grid format (*.adf) files in QGIS. I can display the raster set itself, however, the appropriate attribute data fails to join the spatial dataset.
Can QGIS display the full source raster for ArcGIS?
Or is it a 'proprietary' format that can only be fully displayed in ArcGIS?
The .adf file is one component of an Esri GRID 'file', much like the .shp is one component of a shapefile. The other component files generally aren't or don't need to be accessed individually. If you can load that w0001.adf file and see the raster image, I suspect you're seeing all the data. I opened/added the file in Arc with no issue. In looking at the attribute table for the raster there, there's just a second, coded, numeric value field - you won't see the text strings describing what those coded values are (that info is listed in the metadata).
The data appears to be in three formats: a .mdb in ./Data/, a .tif and some txt files in ./Interchangeable_format/, and an Arc/Info binary coverage in ./GISfiles with a raster layer called wise30sec_fin.
Both the tif and the Arc/Info coverage can be read by R or QGIS via the underlying GDAL library. The tif appears to be just integers that will need to be used for lookups, but the Arc/Info coverage includes those and is a bit richer too, so I'll use that...
Use the raster package to read it in:
> library(raster)
> r = raster("./wise30sec_fin/")
> r
class : RasterLayer
dimensions : 16753, 43201, 723746353 (nrow, ncol, ncell)
resolution : 0.008333333, 0.008333333 (x, y)
extent : -180, 180.0083, -55.98333, 83.625 (xmin, xmax, ymin, ymax)
coord. ref. : +proj=longlat +datum=WGS84 +no_defs +ellps=WGS84 +towgs84=0,0,0
data source : /home/rowlings/Downloads/wise_30sec_v1/GISfiles/wise30sec_fin
names : wise30sec_fin
values : 0, 32156 (min, max)
attributes :
ID MU_GLOBAL MUGLB_NEW COVERAGE CODE CLIMATE_CO NEWSUID COUNT
from: 0 0 0 0 Y-0 502784485
to : 32156 31111 32156 5 C C-32156 WD30032156 51
VALUE30SEC
0
32156
Note this hasn't actually read it into memory because of its size. R will get bits of it as needed, and we have to be careful not to read it all into memory unless we have a lot of memory. You may struggle to process the whole raster in R, so crop it to your study area if you have one.
Note the raster is a single band, and has a set of attributes. This is a data frame that links integer values in the raster to attribute values. Lets look at the first few, by using levels on the raster. The raster is a single band, so we get the first attribute table by extracting with [[1]]:
> levels(r)[[1]][1:4,1:5]
ID MU_GLOBAL MUGLB_NEW COVERAGE CODE
1 0 0 0 0
2 2 2 2 4 A
3 36 36 36 4 B
4 37 37 37 4 A
So to get the information for a location, get the value of the raster at that location and that's the ID in the attributes table:
> r[5000,7000]
4713
> subset(levels(r)[[1]], ID==4713)
ID MU_GLOBAL MUGLB_NEW COVERAGE CODE CLIMATE_CO NEWSUID COUNT
1999 4713 4713 4713 4 D D-4713 WD40004713 8522
VALUE30SEC
1999 4713
Now I can read in one of the data files and look up in that with the NEWSUID code:
> data = read.table("./Interchangeable_format/HW30s_wD1.txt",head=TRUE,sep=",")
The data is one row shorter then the attribute table, so its possible one NEWSUID code is missing:
> dim(data)
[1] 16413 55
> dim(levels(r)[[1]])
[1] 16414 9
and its the empty string which I guess is code for the sea.
Anyway, we can now select the values from the data file since we know the NEWSUID value at r[5000,7000]:
> subset(data, NEWSUID=="WD40004713")
NEWSUID NofComponents SoilUnits Layer PROP_aw MiscUnits PROP_misc
12604 WD40004713 1 GLm100 D1 100 0
Drain DrainProp DrainNum DrainMin DrainMax TopDep BotDep CFRAG CFRAG_std
12604 P 100 2 2 2 0 20 1 1
So that's the fundamentals of looking up data values given the raster and some data. You can do all sorts of clever things like adding the data to the levels(r) but I think the best thing to do might depend on what you actually want to end up doing with the data - if its just sampling at a few points you might want to do something different to if you want to create a whole load of global maps of a quantity in the data files.
There's a useful answer on manipulating raster level attributes here:
but watch out - some of those things might try and load the whole raster into memory and that might be pretty slow or hang your computer.
Alternatively, using exclusively the files in ./Interchange_files, the tif file stores pixel values, which are in the .tsv file, where you can lookup NEWSUID values to look up in the data file. Again, the large size stops me wanting to do this for the whole raster but everything is well-named.
Best Answer
Qgis uses gdal to access .adf rasters, Arcinfo Binary Grids (note: .adf files are also used for Arcinfo vectors). Reading the reverse engineered Arc/Info Binary Grid Format description page one sees
So, no Qgis probably can't read Arcinfo raster attributes. That document was written a long time ago though, so perhaps things have changed.
I don't have access to a vat-enabled raster right now so can't test, but I surmise the structure outlined in the Raster dataset attribute tables Arcgis help is likely quite similar to the vat.adf structure, for those wishing to plug the hole in the format description and perhaps extend the gdal aigrid format driver.