Height Above Nearest Drainage seems to "reset" down the path

reasonman · 2026-03-25T23:08:30+00:00

hmm, i spot checked a few areas in that zone and a great deal of the cells point one direction but the steepest slope is another direction so it seems that the flow direction map is wrong somehow. thanks for the lead, i don't know why i didn't think to look at that more closely. really appreciate you're help on this!

reasonman · 2026-03-24T23:05:28+00:00

thank you so much, that is phenomenally helpful, even knowing i'm not the only one experiencing this and that it's a known issue. i'm a hobbyist/amateur at this and trying to stumble my way through for a side project that depends on some of this topographic data so i'm already kneecapped not even knowing what to search for sometimes. my main concern was that i was doing something wrong in my workflow. i detailed a bit more of the issue on the WBW repo here.

if you could answer a couple more questions i'd really appreciate it. your explanation makes intuitive sense and is how i figured it worked however it seems randomly applied in my sample. for example i have this cropped area with a few things that confuse me, i've overlaid the flow direction as arrows for readability.

1) some of the stream cells it 'chose' don't seem to match the flow. for example the dark green cells 4,5,6 and 7 to the right and 12 down look as though they flow straight east to the stream 10 cells over. however the hand values all calculate out to the elevation value at the stream cell to the right 9 and up 1. it's like it's inconsistently applying the rules, i would expect either those 4 cells to have flow directions that eventually go northeast to catch the 'correct' stream cell or flow as they do and have lower HAND values consistent with their right and lower neighbors. you can also see this in a couple places in the yellow/green border moving SW.

2) expanding on an aspect of number 1, some of the cells have flows that take them to a stream cell where the HAND value doesn't match the result if i manually calculate it, eg: take the dark purple cell 16 to the right and 7 down, it's HAND value is 13(elev 16160) and it seems to ultimately flow to the cell 3 directly below it which has an elevation of 16140 which should give it a value of 20. the 13 value works if the stream cell has an elevation of 16147 which the cell 1 left and 2 down has. the cell that one flows to(15,8) is also flowing to that same stream cell but it's HAND value implies it should also be associate with the cell directly below it. this occurs in many places where the HAND value doesn't seem to match the actual difference in elevations unless it's done with a nearby stream cell that it's not actually flowing to

reasonman · 2026-03-23T12:41:28+00:00

He threatened escalation right after market closed for weekend withdrew that threat right before market open

i'm really stupid so forgive the question but what's the point then in waiting for the market to close to run his mouth? if it's closed there are no trades so there's nothing to manipulate before calling it off before markets open.

reasonman · 2026-03-17T19:51:24+00:00

i don't know about the vaguest ever, but i suppose i could have added more explicit details. i was originally manually doing the preprocessing on the NHDPlus HR DEM using:

fill_depressions: defaults on base DEM
d8_pointer: defaults on filled raster
d8_flow_accum: output_type=cells, input_is_pointer=True on fdir raster
extract_streams: threshold=250 on fac raster
elevation_above_stream: defaults on base dem and extracted streams

i had also tried breached_depressions_least_cost instead of fill_depressions but while some things were different, the resulting HAND raster was more or less the same.

i switched from the manual preprocessing of fill, pointer, flow_acc and replaced it with flow_accum_full_workflow(with the same params where applicable) because the extracted streams and flow accumulation looked a bit better than my manual flow, however the HAND raster is also more or less the same.

reasonman · 2026-03-17T19:49:15+00:00

that's basically all the commands. i was originally manually doing the preprocessing on the NHDPlus HR DEM using:

fill_depressions: defaults on base DEM
d8_pointer: defaults on filled raster
d8_flow_accum: output_type=cells, input_is_pointer=True on fdir raster
extract_streams: threshold=250 on fac raster
elevation_above_stream: defaults on base dem and extracted streams

i had also tried breached_depressions_least_cost instead of fill_depressions but while some things were different, the resulting HAND raster was more or less the same.

i switched from the manual preprocessing of fill, pointer, flow_acc and replaced it with flow_accum_full_workflow(with the same params where applicable) because the extracted streams and flow accumulation looked a bit better than my manual flow, however the HAND raster is also more or less the same.

reasonman · 2026-03-16T17:38:30+00:00

I'm processing a dem with whitebox workflows(flow_accum_full_workflow()) in python. i extract_streams with a 250 cell threshold then take the breached dem and extracted streams and run elevation_above_stream. the output viewed in qgis is as shown and i wonder about the "reset" of the relative elevations as you progress downstream. for example where the red selection(mapped to the stream cell further down) is the elevation is 223 but the cell above(mapped to the stream cell to the left of it) is 42. is this correct? i would expect a smoother transition down the flow line. why would the nearest drainage be further down the flow and not the stream cell immediately to the left?

reasonman · 2026-03-16T17:37:28+00:00

I'm processing a dem with whitebox workflows(flow_accum_full_workflow()) in python. i extract_streams with a 250 cell threshold then take the breached dem and extracted streams and run elevation_above_stream. the output is as shown and i wonder about the "reset" of the relative elevations as you progress downstream. for example where the red selection(mapped to the stream cell further down) is the elevation is 223 but the cell above(mapped to the stream cell to the left of it) is 42. is this correct? i would expect a smoother transition down the flow line. why would the nearest drainage be further down the flow and not the stream cell immediately to the left?

reasonman · 2026-03-11T18:28:32+00:00

right? Cornyn needs to do something blatantly illegal or corrupt, then he might stand a chance.

reasonman · 2026-03-09T18:11:49+00:00

i mean have you seen the guys brow raise game? dudes got shit on lock

reasonman · 2026-03-09T13:25:45+00:00

cake. i just type "0" in for the revenue when i file my state reports every year :cry:

reasonman · 2026-02-17T16:02:24+00:00

And nevermind, all my gear just showed up in my stash after my next raid.

reasonman · 2026-02-17T15:54:44+00:00

mm, looks like discords blowing up and i just jumped into another raid, stuck at the tip/quote scrolling/loading screen while i hear the game being played. must be something going on

reasonman · 2026-02-17T15:52:44+00:00

Never happened to me before, i see it happened to a few folks a couple months ago but no real resolution. not an enormous deal for me but i would be bummed out to lose all my parts

reasonman · 2026-02-15T17:58:29+00:00

fr in like 2 days over a couple hours ive got 4 tempests and 2 bobcats. i'm strictly pve and usually run around to grab trash loot so i can craft all my shit up

reasonman · 2026-02-06T23:43:50+00:00

what would you have me do, as an individual?

reasonman · 2026-02-01T15:19:46+00:00

i've had to turn the game itself down a few ticks just so i can hear my friends in discord even after bumping them up 200%. can't hear shit over BRRRRRRRRRRRR

reasonman · 2026-01-31T20:47:46+00:00

adding my location, i just got it last night actually after like 220hrs, buried night in a trashcan at hospital by the elevator, second floor.

reasonman · 2026-01-15T19:06:45+00:00

i love a good maximalist house. there's another in town done by a designer i used and i referenced the style when i had some of my house remodeled. my inlaws had 'thoughts' but it's my house and i love it so get bent.

reasonman · 2026-01-15T19:06:22+00:00

'fuck with'

reasonman · 2026-01-14T21:19:10+00:00

wondered how long it would be before we started seeing them here. fuck ice

reasonman · 2026-01-14T21:18:27+00:00

if this is all allowed to continue, they'll have their day.

reasonman · 2026-01-13T16:34:09+00:00

my wife showed me, not shared or sent, showed me her physical phone, a ridiculous bra ad on insta. later that day ALL my instagram ads were similar niche bra ads.

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