Man pages matching name qwtrasterdata in section 3:

QwtRasterData.3.en	debian 10 / libqwt-doc
QwtRasterData.3.en	debian 10 / libqwt5-doc
QwtRasterData.3.en	debian 11 / libqwt-doc
QwtRasterData.3.en	debian 12 / libqwt-doc