rem First, convert the input data to vrt, reprojecting from RD to wgs84, and replacing the nodata value at the same time.
rem As gdalwarp does not support AAIGrid as output, we first convert it to VRT, and use gdal_translate to translate it to an ESRI ASCII GRID file.

for %%f in (*.asc) do (
	echo Processing %%f
	"c:/Program Files/QGIS Pisa/bin/gdalwarp.exe" --config GDAL_DATA "c:/OSGeo4W64/share/gdal" -srcnodata -9999 -dstnodata -1 -t_srs EPSG:4296 -s_srs EPSG:28992 -of VRT -r average %%f %%f_intermediate.vrt
	"c:/Program Files/QGIS Pisa/bin/gdal_translate.exe" -of AAIGrid %%f_intermediate.vrt %%f.out
	del %%f_intermediate.vrt
)
Use GDAL to convert ESRI ASCII Grid files in RD to WGS84. Requires a working GDAL installation, e..g. you can use the one that is installed with QGIS, or install it yourself.
Use GDAL to convert ESRI ASCII Grid files in RD to WGS84.
Requires a working GDAL installation, e..g. you can use the one that is installed with QGIS, or install it yourself.

You need to specify:

* the path to the gdalwarp en gdal_translate exe
* the path to the gdal data (specifically gcs.cvs, containing the EPSG definitions)
* the no_data value, if you wish to convert it to something shorter (e.g. -9999 --> -1).