# Linear extrapolation of points using QGIS

I am currently working with hurricane data from NOAA’s IBTrACS. Each gathered data point is separated by three hours. The points and lines can be found in two different data sets on the IBTrACS website. I am trying to add points on the path for every hour. Since storms are nonlinear and change speeds greatly over three hours, I cannot use Densify as that function adds points based on distance.

I will be assuming between each point there is a linear trend. This linear trend also applies to the change in wind speeds (which is an attribute in the data). Shown here is the buffer of the radius of the max wind speed, the data collection points, and the hurricane track, all are of Hurricane Maria. I want to be able to show a constant change in all the features if possible (i.e. the radius of max wind speed for three-hour segment changes from t0=50kts to t3=80kts, but with the hour intervals it would have attributes of t0=50, t1=60, t2=70 and then t3=80).

I have access to QGIS 3.6. I have referenced Extrapolating a line in PostGIS but do not know how to apply it to QGIS. • Please decide which of ArcGIS Pro and QGIS you wish to ask about in this particular question. – PolyGeo Nov 8 at 2:29
• In QGIS you can use `densify by interval` to add more vertices to the line layer, then use `extract vertices` to convert the vertices to points. – csk Nov 8 at 18:25
• Can you please describe more in detail the way or provide a graphic/sketch of how would you locate `'one-hour-points'` between `'three-hours-points'`, what trajectories will they obey? Moreover, I was wondering about the speed of trajectory, is it inherited from the buffer, is not it? Btw what happens on the overlap of two speed-buffers? – Taras Nov 14 at 6:58
• @csk is there a code I could use to densify by interval where the interval would be one-third and then two-thirds of the distance from vertex to vertex? – John S. Nov 15 at 18:00
• The `densify` algorithm doesn't do variable intervals. – csk Nov 19 at 17:54