Thank you for your response. It still doesn't match with the distance I measure in QGIS. However, apparently I work with the wrong CRS in QGIS, right? ... I guess this would mean that I am also measuring wrong distances in QGIS and I should rather rely on e.g. GoogleMaps to measure the correct distances ... is that correct? The measured distances in GoogleMaps and FEFLOW (based on the shape saved under use of WGS84 UTM Zone 29N) correspond quite well. I guess I can then just change the CRS properties of my entire project in QGIS ... ? Thank you for your patience and great support!

IN fact they are all a little difference. A distance which I measure in QGIS as 7655 metres is in FEFLOW 9152 metres when I saved the shape using the WGS 72 / UTM zone 40N CRS and 6100 metre when I saved under use of WGS 72 / UTM zone 40N ... ;(

I now tried "ETRS89 / Portugal TM06". Should that be correct? At least the shape has the correct angle now.

Thank you a lot! I now selected WGS 72 / UTM zone 40N (for the south of Portugal). The result is much better. Actually, it could be correct. The shape is only rotated by approximately 60° but I can live with that I guess. Thanks!

Hi @ahmadhanb! Thank you for your response. Unfortunately, the resulting layer from saving my shape file in EPSG 32654 is empty or at least I don't see any shape in QGIS, That's also the case when I open the shape file in FEFLOW ... it's completely empty. Is there any other CRS with which I could try?

Thanks for your response! I am not exactly sure how to find out. However, if I go on Layer Properties -> General it days "Selected CRS (EPSG:4326, WSG 84) for coordinate reference system). Is that what you meant?

This still exports the ID which is a little bit annoying but certainly something I can deal with!<br/> X,Y,ID,ELEV -7.45249953993674,37.1912500968475,222308,0.000 -7.45208287327007,37.1916667635141,222308,0.000 -7.45249953993674,37.1920834301808,222308,0.000 -7.45277731771452,37.1916667635141,222308,0.000 <br/> Thank you both for your support!! :)

Hi @ThingumaBob! Thank you very much for your response! Unfortunately, this doesn't do it. I modified my question to clarify what I would like to do :)