I have a variety of raster files from the exact same study area including different values (hourly mean radiant temperature). Is it possible to find out the overall min/max values (not each individual one)?
[GIS] QGIS find overall min/max
qgisrasterstatistics
Related Solutions
Another possibility is that you are working on renamed layers. When I did raster calculations I often got faulty layers (1.79769e+308 values) generated in QGIS 3x, without any error. I tested on QGIS 3.2 and 3.4.3.
There is a raster calculator bug caused by renaming of layers that only was completely fixed on 2019-01-02. See issue 20601, it is fixed, but has yet to make it to a stable build. As a workaround, in 3.4.3, the Gdal raster calculator in the Processing Toolbox seems to work, as is the one in the main menu "Raster - Raster Calculator"
Using gdal in python, you could open the first file and use those values as your "base-values". Then looping over the rest of your files, comparing the base-values with the just opened values and each time selecting the maxes (or minuses). Something like this:
# Create a list of files, have a look at glob.glob() to list many files.
files = [r"D:\some_path\MOD11A1.A2005001.h28v07.005.2007347211605.hdf",
r"D:\some_path\MOD11A1.A2005002.h28v07.005.2007348210508.hdf",
r"D:\some_path\MOD11A1.A2005003.h28v07.005.2007348221535.hdf",
r"D:\some_path\MOD11A1.A2005004.h28v07.005.2007349081734.hdf",
]
# Select the first file.
filepath = files[0]
# Get some general info from that file.
ndv, xsize, ysize, geot, projection = get_geoinfo(files[0], 0)
# Open the file twice to get your "base-values".
max_values = open_hdf_file(files[0], 0).astype(np.float)
min_values = open_hdf_file(files[0], 0).astype(np.float)
# Set the NDV pixels to NaN values.
max_values[max_values == ndv] = np.nan
min_values[min_values == ndv] = np.nan
# Loop over the rest of your files.
for filepath in files[1:]:
next_array = open_hdf_file(filepath, 0).astype(np.float)
next_array[next_array == ndv] = np.nan
max_values = np.nanmax(np.array([max_values, next_array]), axis = 0)
min_values = np.nanmin(np.array([min_values, next_array]), axis = 0)
# Save the created arrays as, for example, geotiffs.
out_filepath_max = r"C:\some_path\max_values.tif"
out_filepath_min = r"C:\some_path\min_values.tif"
geo_info = (ndv, xsize, ysize, geot, projection)
create_geotif(out_filepath_max, max_values, geo_info)
create_geotif(out_filepath_min, min_values, geo_info)
Using these function:
import gdal, osr
import numpy as np
def open_hdf_file(filepath, subdataset):
hdf_file = gdal.Open(filepath)
data = gdal.Open(hdf_file.GetSubDatasets()[subdataset][0])
scale_factor = float(data.GetMetadata()['scale_factor'])
array = data.ReadAsArray() * scale_factor
return array
def get_geoinfo(filepath, subdataset):
sourceds = gdal.Open(filepath, gdal.GA_ReadOnly)
sourceds = gdal.Open(sourceds.GetSubDatasets()[subdataset][0])
ndv = sourceds.GetRasterBand(1).GetNoDataValue()
xsize = sourceds.RasterXSize
ysize = sourceds.RasterYSize
geot = sourceds.GetGeoTransform()
projection = osr.SpatialReference()
projection.ImportFromWkt(sourceds.GetProjectionRef())
return ndv, xsize, ysize, geot, projection
def create_geotif(out_filepath, array, geo_info):
datatypes = {gdal.GetDataTypeName(i).lower() : i for i in range(1, 12)}
driver = gdal.GetDriverByName('GTiff')
dataset = driver.Create(out_filepath, geo_info[1], geo_info[2], 1, datatypes[array.dtype.name])
array[np.isnan(array)] = geo_info[0]
dataset.GetRasterBand(1).SetNoDataValue(geo_info[0])
dataset.SetGeoTransform(geo_info[3])
dataset.SetProjection(geo_info[4].ExportToWkt())
dataset.GetRasterBand(1).WriteArray(array)
dataset = None
Note that:
This script would only work with the images from the same scene.
The second input in the functions get_geoinfo and open_hdf_file (all zero in the example) is used to choose which subdataset to use from the hdf-files. Have a look at the code below to make sure you select the right subdataset:
hdf_file = gdal.Open(filepath)
hdf_file.GetSubDatasets()
Best Answer
You could use Statistics for rasters tool (in
Processing Toolbox | SAGA | Geostatistics).It will give you
MinimumandMaximumraster, each cell represents the minimum and maximum value across the layers. (There are alsoPercentile,Arithmetic Meanetc... if you like).If you want to have single overall
minimumormaximumvalue, next step will be Raster Layer Statistics tool (inProcessing Toolbox | QGIS - Raster Analysis). GiveMinimumraster from above operation to this tool, thenMINvalue is the overall minimum.