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)
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?
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.
@@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.
Thank you so much for the video. It is really helpful.
thank you for tutorial, really useful, succes for your channel👍
Hello! This was incredibly helpful to watch - just wondering if you have a source from where you got the instructions for the calculation? Thank you!
great tutorial, nice
thanks, you did amazing work
Merci beaucoup pour ce tutorial.
Thanks alot.
Thank You, Sir
muchas gracias!!
Thanks
Thank you so much
Hello, thank you for sharing. In case the cell size is not the same value between X and Y, which value would you use to calculate?
Thanks!!!
merci
thank you so much! anyway did you know the classification for TWI?
What's the difference between wti ant cti?
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!
Did you ever figure this out? I've been looking for information on this method as well as it seems to produce a highly reliable output.
@@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)
@@sarajohnson9777 Why is the flow accumulation not used directly, why is it scaled?
Como saco la información de humedad a partir de este último índice??
You helped me, thanks sir
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?
its possible you are not in a projected coordinate system?
Just resample your data and choose suitable cell size
Use arc toolbox . data management. raster. raster processing. Resample
How about atribute table?
What are the meanings of 1.570796 and 90?
+1
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.
Elizabeth Sandoval Fritz thank you so much
the cell size of my dem is very low, 0.007.
what to write
Project your DEM into UTM. Yours seem to be in wgs
The "compound topographic index (CTI)", is not the same
as the "topographic wetness index (TWI)"
What does taking tan of slope means; slope is already tan of angle,theta!
That is exactly what i was going to ask...
@@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.