dst_band->RasterIO(GF_Write, 0, 0, quad1_scans, quad1_pixels, outarr[0], quad1_scans, quad1_pixels, GDT_Float32, 0, 0)

This line of code is using the RasterIO() function of a GDAL band object (dst_band) to write out a 2D array of floating point values (outarr[0]) to a GeoTIFF file.

The function call specifies that the data should be written in "band sequential" order, where all the values for the first row are written out, followed by all the values for the second row, and so on. The start point for writing out the data is (0,0), which is the top-left corner of the image.

The size of the output array is specified by the values of quad1_scans and quad1_pixels, which are the number of columns and rows in the array, respectively. The output data type is set to GDT_Float32, which is the GDAL enumeration value for 32-bit floating point values.

Finally, the last two arguments of the function call are set to 0, which means that no special options or flags are being used.