I use Proj4js for this. When adding the definition from spatialreference.org I noticed a difference with the definition that is embedded in my PostGIS database:
// Source: PostGIS SRID 28992 from database "+proj=sterea +lat_0=52.15616055555555 +lon_0=5.38763888888889 +k=0.9999079 +x_0=155000 +y_0=463000 +ellps=bessel +towgs84=565.417,50.3319,465.552,-0.398957,0.343988,-1.8774,4.0725 +units=m +no_defs" // Source: http://spatialreference.org/ref/epsg/amersfoort-rd-new/proj4js/ "+proj=sterea +lat_0=52.15616055555555 +lon_0=5.38763888888889 +k=0.9999079 +x_0=155000 +y_0=463000 +ellps=bessel +units=m +no_defs"
The difference being
+towgs84=565.417,50.3319,465.552,-0.398957,0.343988,-1.8774,4.0725 that is present in the PostGIS definition but not in the spatialreference.org definition.
Is this a meaningful difference? If so, what does this part of the string define?