Jimmy

Hi guys, is it at all possible to buy a GPS/ altimeter instrument, that will give what height you are above the ground you are flying over, instead of height you are above sea level. I've watched many videos on paramotoring in the USA, and most of their instruments show both, above sea level and actual height above the ground. I've searched every app in the UK, but can't find one that gives the height above the ground. I can't understand why not, if the GPS map you are using has the above sea level information, why not give another reading of the same, with this above sea level subtracted, making it, above ground level. Please help