KGA Irrigation Toolsផ្ទាំងអន្តរកម្ម
Generate River or Stream for ROI
ទាញយក Copernicus DEM ឥតគិតថ្លៃសម្រាប់តំបន់មួយ រួចស្រង់បណ្តាញទន្លេ និងអូរ ដោយមានចំណាត់ថ្នាក់ និងការពិនិត្យ។
- រកឃើញនៅឯណា
- Processing ▸ Toolbox ▸ KGA Toolbox ▸ KGA Irrigation Tools ▸ Generate River or Stream for ROI
- លេខសម្គាល់ algorithm
- kga:generate_stream_roi
- ប្រភេទឧបករណ៍
- Interactive dialog — modeless, needs the QGIS window and an internet connection
ទិដ្ឋភាពទូទៅ
Downloads the free Copernicus DEM, cuts it to the area, fills its depressions, routes the water downhill, and draws a stream wherever enough ground drains through a cell. Each segment is numbered (Strahler order), measured, and graded for confidence; an optional comparison with OpenStreetMap or your own layer finds streams that only one network has.
How much stream? (Detail)
A cell becomes stream when at least a certain area of ground drains through it. That one number controls the whole network.
| Detail | Contributing area | Use it for |
|---|---|---|
| Major rivers only | 25 km² | The skeleton of the drainage. Needs a large area; below about 100 km² there may be nothing this big. |
| Main streams (default) | 5 km² | The streams a map would normally show. |
| Detailed network | 1 km² | Adds smaller tributaries; good for a catchment of tens of km². |
| Very detailed | 0.2 km² | Every gully that gathers water. Includes channels dry most of the year, and more false streams on flat ground. |
| Custom | 0.01–5000 km² | Anything in between. |
| Match a drainage density | 0.1–5 km/km² | Lets the tool pick the area. Natural catchments run roughly 0.5 (sparse) to 2 (dense). |
At 30 m, 1 km² is about 1,100 cells. A threshold below 3 cells is raised to 3, and one that would make a quarter of the area "stream" is refused as a typo.
ប៉ារ៉ាម៉ែត្រ
| ផ្ទាំងគ្រប់គ្រង | ប្រភេទ | តម្លៃលំនាំដើម | ការពិពណ៌នា |
|---|---|---|---|
| DEM | Combo box | Copernicus GLO-30 | GLO-30 (the one to use), GLO-90 (for a very large area), or Local DEM: a raster layer or a DEM file. A local DEM is read from band 1 as metres, must cover the area, and needs no internet. No Copernicus attribution is added to its layers. |
| Area | Combo box | Current map extent | Current map extent, Extent of a layer, Boundary of a polygon layer (cut to the shape; optional Selected features only), or Draw a rectangle or polygon on the map. |
| Detail | Combo box | Main streams | See the table above. |
| Include upstream area | Combo box | Off | Off, 2, 5 or 10 km. Streams that rise outside the area are otherwise cut short at its edge and look smaller than they are. The saved DEM then includes the margin. |
| Smooth the lines | Boolean | off | Rounds off the cell-by-cell steps. LENGTH_M is measured along the cell path before smoothing. |
| Symbology | Combo box | By stream order | By stream order (blue, wider = higher order) or By check confidence (green High, amber Medium, red Low). |
| Compare with | Combo box | None | OpenStreetMap rivers and streams (needs internet) or A line layer of my own (optional Selected features only). |
| Match distance | Number | about three DEM cells | How close the other network must be for a stretch to count as matched — 90 m at 30 m. |
| Output CRS | Combo box | UTM zone of the area | Default keeps streams, slopes and catchment areas measured in metres. Or Current project CRS, WGS 84 as published, or a Specified CRS. |
| Output folder | Folder | temporary | Empty means a temporary folder, which QGIS deletes when it closes. |
| Name | Text | — | Base name: <name>_DEM.tif, <name>_streams.gpkg, <name>_report.txt, and optionally <name>_flow_accumulation.tif. |
| Also save the flow accumulation raster | Boolean | off | Contributing area in km² for every cell. Useful to judge the threshold or pick catchment outlets. Added to the map switched off. |
របៀបប្រើ
- Open KGA Irrigation Tools > Generate River or Stream for ROI.
- Choose the area. For a drawn area, click Draw rectangle or Draw polygon and draw on the map.
- Pick the detail level. Optionally add an upstream margin and a reference to compare with.
- Pick an output folder, or leave it empty for a temporary one.
- Click Generate streams. Click Stop to cancel; nothing is added to the map.
- Read the report that opens when the run finishes, also under Last report.
លទ្ធផល
លទ្ធផលដែលប្រកាស
| ឈ្មោះ | ប្រភេទ | ការពិពណ៌នា |
|---|---|---|
| STREAM_ID, NEXT_ID | Integer | The segment, and the one it flows into (0 at an outlet). |
| STRAHLER | Integer | Strahler order: 1 for a source; two equal orders meeting make the next one up. |
| LENGTH_M | Number | Length along the cell path, before smoothing. |
| UP_KM2 | Number | Ground draining to the end of the segment, in km². |
| ELEV_UP, ELEV_DN | Number | Elevation at the start and end, from the depression-filled DEM. |
| SLOPE_PCT | Number | Fall along the segment, in percent. |
| FILL_M | Number | The most water the DEM had to pour into a depression to carry this stream across it. |
| RELIEF_M | Number | How far the stream sits below the ground around it (7 × 7 cells). |
| CONF, FLAGS | Text | Confidence grade and the reasons behind it. |
អ្វីដែលអ្នកទទួលបាន
<name>_streams.gpkg— layerstreams, one line per segment between junctions, with the fields listed above.- A
stream_checklayer when a reference was used and the networks differ: lines ofKINDextra(in the DEM, not the reference) andmissed(in the reference, not the DEM). <name>_DEM.tifand<name>_report.txt.
Is the result any good? (Checks)
A network traced from a DEM is a model of where water runs, not a survey of where streams are. Internal checks run on every job: FLAT (falls under 0.1 %), FILLED (crosses a depression filled by 8 m or more), NOVALLEY (sits less than 1 m below its surroundings) and EDGE (starts at the edge of the data). Two or more of the first three give Low confidence, one gives Medium, none High.
Read the numbers with care. A reference can be incomplete — OpenStreetMap often is in the countryside — and a DEM stream can be a real gully that carries water only after rain. Agreement normally rises with stream size. Not matching does not prove a stream wrong.
កំណត់សម្គាល់ និងដែនកំណត់
- Large areas. Routing needs about 110 bytes of memory per pixel. Above about 6 million pixels (roughly 75 km square at 30 m) the tool asks before it starts, with a sterner warning above 30 million. Above 100 million pixels it refuses — use a smaller area or the 90 m DEM.
- Depressions are filled. Every cell drains out of the area: a lake or a real closed basin is routed across, not stopped. Streams therefore cross reservoirs; look at the
FILLEDflag. - Edges. Water leaves the area at its edge, and a cut-to-shape area treats the shape's outline the same way. Streams near the edge may be missing upstream length unless an upstream margin is used.
- The Copernicus DEM is a surface model, so a stream under dense canopy or through a built-up area can be displaced.
- Network use: the Copernicus DEM bucket on Amazon S3, and — only with the OpenStreetMap comparison — the Overpass servers. Only the area's bounding box is sent.
- Attribution is required: Copernicus DEM © DLR e.V. and © Airbus Defence and Space GmbH, under COPERNICUS by the European Union and ESA. OpenStreetMap data is © OpenStreetMap contributors (ODbL).