Thank you for your sharing. I just have some questions related to your workflow: 1- What it the original formula you use to calculate CTI? 2- Why don't you use DEM filled? 3- The cellsize should be square meter, but I found that you use only 27.9m instead of square of 27.9. Do you have a reason for that? 4- In the formula, Tan(slope_degree) is fine. Why do you need new Slope (=slopeDEM *1.57/90) ?
Hello! Does anyone know the name of the algorithm/method that was used to calculate TWI in this video? Apparently there are a lot of ways in which you can calculate TWI. For example, you can check Sørensen et al. 2005 "On the calculation of the topographic wetness index: evaluation of different methods based on field observations" for a comparison between methods. But which one is this one? Thank you!
@@AdrianCupHolder a friend of mine just sent me the citation for this: www.tandfonline.com/doi/abs/10.1080/02626667909491834 which appears to be the origin of this calculation. Essentially, the parts of the final equation TWI= ln(α/tan β) are just being step-wise calculated from your DEM in this tutorial. So the alpha represents your scaled flow accumulation and tan beta represents the slope (tangent of the slope)
That's the convertion from degrees to radians. It's the same as multiplying "slope*pi/180", but in this case, the term "pi/180" was simplified dividing by 2. This is because ArcGIS works with trigonometrical functions (Tan, in this video) based on radians, not degrees. I'd just dicover this 2 days ago.
Thank you, i have a question with the project raster: when i choose project raster to convert the projection i select 'cell size = 10' I have tried this a few times and the output is with cell size x and y =0.00011960841, i can continue with the instructions but this cell size doesn't make sense?
@@rijurekhodasgupta9008 sorry, bust seems I got the answer. The slope tool only calculates angle, not the tangent of this angle. Slope is, in fact, tangent of angle, say theta, ie ,it is rise over run.
