Q:

Find Point Along Line at Certain Distance

We have software that returns '5143m from PointA on PathB' and I need to know where that would be without using the measuring tool and snapping to manually trace the line. I am not looking to measure distances between points on a line nor find the distance from points to a line. Is there a plugin I can use or a native feature?

I need to figure the physical location of a point on a line (Point X, Line A) given the point at the start of the line (Point A) and a distance along the line. I.e., if I am given '4000m from Point A on Path B', then manually tracing Path B for 4000 meters from Point A should give me the location of Point X; whatever solution we find here should return the same result, saving me the tedium and time (I have quite a few of these to do).

I've done some more searching via linked questions, and solving this problem in ArcGIS would involve Linear Referencing and Interpolation. Is there something similar for QGIS?

The line I need to be traced is not straight; it is a polyline with vertices, turns, etc.

A:

In QGIS 2.18 was introduced a new feature that does the job you seek.
The function is line_interpolate_point (geometry, distance), to be used in calcolatatore QGIS fields.
STEP 1: Create a new field 'wkt_field' (Text 255) and populate it with function:   geom_to_wkt( line_interpolate_point  ($ geometry, distance value));
STEP 2: export the layer as a CSV;
STEP 3: Load the new file with 'add layer delimited text' and select WKT

