I need help to solve an issue with the sink removal tool...
Actually, I'm working with a regional DEM from Peru at 3s resolution per pixel, I tried to fill sinks with -the sinks removal- tool, and the results are a little suspicious because I don't know what the threshold means..... I know that the tool means threshold like "a maximum depth that will be considered a sink to remove" but I don't know how it works, for example if I choose a threshold considering 2 meters as my maximum depth to remove, some areas will fill more than 2 meters in some cases I get filled around 20-30 m btw. in other cases when I choose a threshold with 20 to >50 m in many cases the results are similar like consider 2 m as the threshold or it doesn't fill sinks as I spect. Then...... I don't know what's happening~~~~
I had been searching for more information about it, but no one explained what about the threshold works.
Next, in the picture, we can watch an example result of a sinks removal tool with a threshold of 2 m, the red line is the original DEM and the black line is the DEM-filled sinks.
(In this process In't looking to use other tools like Wang & Liu method, because I'm trying to understand what these tools do).
first of all you should work with projected coordinates, i.e. same units in x,y,z.
The threshold height describes the depth of sinks that get filled. Depending on the size of the sinks, you can get slightly higher fill heights when you use an epsilon greater zero. The epsilon is used to preserve a minimum gradient on flat areas (filled sinks) in order to evaluate flow paths later. In order to compute slope etc. your units should be the same in x,y,z.
Best regards,
Volker
PS: please don't post the same question in different forums
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I understand I should work in same projected coordinates, I was testing with UTM and Geographic cordinates system and the results are the same (filling results exceed the threshold I chose). Then I don't know what's doing Sink Drainage route detection and Sink Removal tool when I put a lower or higher threshold because the results are totally similar with diferent threshold, for example with which one of the next threshold (0.000001, 0.00001, 0.0001, 0.01, 1, 2, 3, 4 or 5) to many sinks get filled greater 5m, even working at the same projected coordinates.
That is the reason I was confused about how Sink Drainage Route Detectiond and Sink Removal tool works when we put a threshold.
Best regards,
APT
PS: About post the same question, Sorry It won't happen again.
Last edit: abraham pacheco tapia 2024-02-13
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I've tested this myself and I must admit that I misinterpreted the threshold parameter. It's not completely obvious, but it seems that it applies not to a single sink in case sinks / flow routes are connected. It is evaluated recursively, so you can't use it to prevent the filling of deeper sinks in case they are not completely isolated.
The only way (and maybe this would be worth a special tool) I see now is to fill the sinks (with any of the sink filling tools available) and then evaluate each sink depth in order to decide which sinks are deeper than the desired filling depth. These could then be masked and the filling removed.
Best regards,
Volker
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
I need help to solve an issue with the sink removal tool...
Actually, I'm working with a regional DEM from Peru at 3s resolution per pixel, I tried to fill sinks with -the sinks removal- tool, and the results are a little suspicious because I don't know what the threshold means..... I know that the tool means threshold like "a maximum depth that will be considered a sink to remove" but I don't know how it works, for example if I choose a threshold considering 2 meters as my maximum depth to remove, some areas will fill more than 2 meters in some cases I get filled around 20-30 m btw. in other cases when I choose a threshold with 20 to >50 m in many cases the results are similar like consider 2 m as the threshold or it doesn't fill sinks as I spect. Then...... I don't know what's happening~~~~
I had been searching for more information about it, but no one explained what about the threshold works.
Next, in the picture, we can watch an example result of a sinks removal tool with a threshold of 2 m, the red line is the original DEM and the black line is the DEM-filled sinks.
(In this process In't looking to use other tools like Wang & Liu method, because I'm trying to understand what these tools do).
Hi,
first of all you should work with projected coordinates, i.e. same units in x,y,z.
The threshold height describes the depth of sinks that get filled. Depending on the size of the sinks, you can get slightly higher fill heights when you use an epsilon greater zero. The epsilon is used to preserve a minimum gradient on flat areas (filled sinks) in order to evaluate flow paths later. In order to compute slope etc. your units should be the same in x,y,z.
Best regards,
Volker
PS: please don't post the same question in different forums
Hi Volker,
I understand I should work in same projected coordinates, I was testing with UTM and Geographic cordinates system and the results are the same (filling results exceed the threshold I chose). Then I don't know what's doing Sink Drainage route detection and Sink Removal tool when I put a lower or higher threshold because the results are totally similar with diferent threshold, for example with which one of the next threshold (0.000001, 0.00001, 0.0001, 0.01, 1, 2, 3, 4 or 5) to many sinks get filled greater 5m, even working at the same projected coordinates.
That is the reason I was confused about how Sink Drainage Route Detectiond and Sink Removal tool works when we put a threshold.
Best regards,
APT
PS: About post the same question, Sorry It won't happen again.
Last edit: abraham pacheco tapia 2024-02-13
Hi,
I've tested this myself and I must admit that I misinterpreted the threshold parameter. It's not completely obvious, but it seems that it applies not to a single sink in case sinks / flow routes are connected. It is evaluated recursively, so you can't use it to prevent the filling of deeper sinks in case they are not completely isolated.
The only way (and maybe this would be worth a special tool) I see now is to fill the sinks (with any of the sink filling tools available) and then evaluate each sink depth in order to decide which sinks are deeper than the desired filling depth. These could then be masked and the filling removed.
Best regards,
Volker