using QGIS 18.16
I am trying to figure out how to cal a reverse azimuth. Basically the opposite direction. So if i have a azimuth of 163, I subtract 180 which gives me -17. I some how need to write a script or a field calc to then , for only the '-', numbers subtract that number form 360. which would give me 343 as the reversed azimuth.
[GIS] Calculating a reverse Azimuth
azimuthqgis
Related Solutions
You need to cast your denominator to a float (decimal) value. See this thread: Why is this field calculator expression evaluated incorrectly when using Python syntax?
Your output field also must accept decimal values (i.e. cannot be an integer field).
Internally you cannot modify Row Numbers. Your calculation into a new field is the number of rows - $rownum:
This will reverse the $rownum into a field. $rownum (row number) objects cannot be modified as they are handled by the driver/database. In the case of shapefiles they are transient as edited features move to the end and then get compressed back to 0 based, unique and ascending on save edits.
Best Answer
Try
if( "azimuth" < 180, "azimuth" + 180, "azimuth" - 180)