Mesh consists of vertices(points) that are topologically connected to form edges. Mesh data is a hybrid data model that represents data in form of irregular grids that store several components such as temporal components and spatial components. But what do you do when you working with data that can not be correctly represented in raster or Vector data format? When it comes to Geospatial data most people only think of vector or raster formats. When to use mesh data and not vector or raster.Definition of mesh data as first-class data format similar to vector and raster formats.Gdal_translate -co tiled=YES -ot Byte test.vrt test_byte.This article will cover the following areas. REM Write out a Byte with no compression TIFF file vrt is the input (from buildvrt), the second is the output REM Write out a Byte with LZW compression TIFF file vrt is the virtual output, the second is the input Gdal_translate -co tiled=YES -ot Byte test.vrt test_byte.tifĭu -h test_byte_lzw.tif #My file uses random 0-31 values so will always be much bigger compressed than "real" data which compresses better.īand 1 Block=21768x1 Type=Float32, ColorInterp=Gray # Write out a Byte with no compression TIFF file Gdal_translate -co compress=LZW -co tiled=YES -ot Byte test.vrt test_byte_lzw.tif # Write out a Byte with LZW compression TIFF file Gdalbuildvrt -srcnodata -3.4E+38 -vrtnodata 255 test.vrt test.tif Gdal_translate -co compress=LZW -co tiled=YES test.tif test_lzw.tif Prior to running the code below, set the path for files with cd followed by path (e.g. It is opened separately from QGIS Desktop, a different program available from the start-up menu. To use the LZW compression method (or other lossless method), choose Profile : Default and then add a compression method with the big green + and enter manually COMPRESS under Name and LZW under Value.įor full functionality of GDAL Translate, use OSGeo4W Shell in Windows (or a terminal shell in Linux/MacOS). The options for GDAL Translate (convert format) in the GUI window are somewhat hidden. (Note the -3.39999999999999996e+38 is just because gdalinfo is printing -3.4e+38 with floating point representation error, your NoData is -3.4e+38 which is the minimum value of the Float32 range) In the example below, I use gdalbuildvrt to change the NoData value from -3.4e+38 to 255 which is within the Byte data range 0-255. You can set any value (within your data type range) as NoData, you don't have to use 0. Lossy compression methods are good for data where filesize is more important than absolute data integrity, such as a stretched aerial photo purely for display. JPEG compression resulted in image degradation because it is a lossy compression method, LZW and DEFLATE are lossless (input value will always = output value). The resulting file is bigger because it has no compression. That gives me the size Windows indicates for my 8-bit raster without compression. Metadata of original file Size is 21768, 12920 It seems that 0 worked in my case but I may have files with 0-values that are meaningful and I wouldn't know how to convert the multidecimal NoData value from the Float to an integer value that is not confused with actual zero values in the dataset. I had difficulty setting the NoData value.using JPEGwith 100 resulted in some values being +/-1 of the values they should be and some random additional pixels) default, no compression, Low compression, High compress, JPEG compression) but I was not successful in reducing file size while maintaining data quality (e.g. I noticed that the original file had COMPRESSION=LZW and tried to use various compression formats under Profile (i.e. The resulting file is BIGGER than my original file (from 31MB to 268MB). I have used the Translate (convert format) tool available from GDAL to change the data type from Float32 to Byte (following these instructions). I think that the optimal method to store the data is as unsigned 8 bit integer (QGIS Byte) as there are no decimal values and the maximum value is below 255. I have realized that the values are stored as Float32 with NoData Value=-3.39999999999999996e+38 (see raster information below). I have a raster file (.tif) that contains integer values from 1 to 31.
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