I would like to measure the shortest distance from multiple points to a any part in a coast line of three different costs. How do I do this with QGIS or with SAGA GIS?
You can achieve this with the
Join attributes by nearest algorithm in QGIS. It returns not only the join of attributes (which costline is the nearest) but also the distance between the input geometries (shortest line between points and lines/polygons). It also yields the X and Y coordinates of the nearest point on the coastline which could be used for visualizing the shortest line or calculating ellipsoid based distances.