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I have modis land cover MCD12Q1 data .Its in the sinusoidal projection (.hdf native format ). I have to study the land cover characters from the data for which i have to convert them into .tif format , so that i can use the data in ENVI and arcgis . I used the MRT tool to mosaick and reprojected the tiles into WGS84 Geographic coordinate system converting them into .tif format. When i opened the .tif data , there were just distortion and just black and white strips .I checked the projection type of raw files in arc gis which showed "unkown datum based upon the custom spheroid sinusoidal " . how do i transform the .hdf files to .tif files of valid projection without distortion ?

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NASA provides some HEG tools for this

you can also use gdal for this task (see this answer for the conversion, and below for he reprojection), or use the parameters of the projection to define your custom projection in ArcGIS (using copy and modify from the sphere-based sinusoidal projection to change the radius of the sphere). Note that projection will distort your image, always ! And with categorical data, you need to select a nearest neighbour resampling (or a mode resampling, but in this case nearest neighbour is faster and will give you the nearly the same output) gdalbuildvrt stitched.vrt tile1.tif tile2.tif ... tileN.tif gdalwarp -r near -s_srs "+proj=sinu +lon_0=0 +x_0=0 +y_0=0 +a=6371007.181 +b=6371007.181 +units=m +no_defs" -t_srs "EPSG:4326" stitched.vrt outfile

Note that projection induces

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