Here is a video I just created to show you how Lichti can be used for a project like this.
I will give a brief overview of what I am doing in the video.
My goal is to plan a mission that flys my Mavic right along a sidewalk that is next to a local school and down the street maintaining the perfect line right next to the sidewalk.
I first open the online web page that Lichti makes available to preplan flights known as "missions".
Then I click in the lower left hand corner on New to create a new mission.
Then I just click on the map kinda close to where I want my first waypoint to be set.
Notice that the way point is not perfectly positioned right above the edge of the sidewalk. Its off a little. No worries!
Then there is a dialoge box that is presented to the right that has alot of values within it. The upper two relate to the Latitude and Longitude
Since I want the first waypoint to be closer to the edge of the sidewalk I click in the Latitude box directly and remove everything while leaving 39.16 I then enter a 2 that replaces the 1. So the Latitude becomes 39.162
When I press enter then the waypoint shifts upwards and aligns itself with the edge of the sidewalk. Then its just a matter of clicking on down the street to add more waypoints on the Longitude ( I intentionally click off the straight line as I know I can just bring it back to be straight) and not worrying about the position too much on the Latitude as I just click in the box for Latitude and adjust it to be 39.162 and it gives me a perfectly straight flight path that flys along the sidewalk.
There are all kinds of other things that one can adjust like - hard 90 degree turns or radius-ed turns position of the gimbal/camera in relation to a point of interest. etc.
Here is the example video