KGA Irrigation Toolsផ្ទាំងអន្តរកម្ម
Generate Contour for ROI
ទាញយក Copernicus DEM ឥតគិតថ្លៃសម្រាប់តំបន់មួយ រួចគូសបន្ទាត់កម្ពស់ ព្រមទាំងដាក់រចនាបថ និងស្លាករួចស្រេច។
- រកឃើញនៅឯណា
- Processing ▸ Toolbox ▸ KGA Toolbox ▸ KGA Irrigation Tools ▸ Generate Contour for ROI
- លេខសម្គាល់ algorithm
- kga:generate_contour_roi
- ប្រភេទឧបករណ៍
- Interactive dialog — modeless, needs the QGIS window and an internet connection
ទិដ្ឋភាពទូទៅ
Makes contour lines for any area of interest in one step. The tool downloads the free Copernicus DEM (30 m or 90 m, from the AWS open-data bucket — no account and no API key), cuts it to the area, traces the contours at the chosen interval and adds them to the map: dark and thick for the main contours, thin and grey for the rest, with elevation labels.
The job runs on a background task, so QGIS stays usable. One progress bar covers all of it — reading and cutting the DEM, tracing the lines, marking main and sub contours and, if ticked, smoothing.
ប៉ារ៉ាម៉ែត្រ
| ផ្ទាំងគ្រប់គ្រង | ប្រភេទ | តម្លៃលំនាំដើម | ការពិពណ៌នា |
|---|---|---|---|
| DEM | Combo box | Copernicus GLO-30 | GLO-30 (about 30 m) or GLO-90 (about 90 m), or Local DEM to use one you already have: a raster layer from the project or any GDAL raster on disk. It may be in any CRS, but must have one and be north-up. |
| Area | Combo box | Current map extent | Whole DEM (local DEM only), 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. |
| Interval | Number 0.1–5000 m | — | Vertical distance between contours. Lines fall on whole multiples of it (0, 10, 20 … for 10 m). |
| Main contour | Number 2–20 | — | Every Nth contour is a main contour. |
| Smooth the lines | Boolean | off | Rounds off the pixel steps (one round of corner cutting). Better looking, about twice the vertices, and the lines move by less than a pixel. |
| Symbolize | Boolean | on | Main contours dark and thick (0.5 mm), sub contours grey and thin (0.15 mm). Untick for QGIS's default line style. |
| Labels | Combo box | Main contours only | Main contours only, All contours, or No labels. |
| Terrain surfaces | Check boxes | off | Optionally derive a Hillshade (lit from the north-west), Slope (degrees) and Aspect (0–360° clockwise from north) from the DEM. |
| Add random spot height | Boolean + number | off | Scatter spot heights over the area, spread evenly rather than clumped. Each is a small black dot with its height beside it, as on a topographic map, saved as the spot_heights layer. |
| Output CRS | Combo box | Current project CRS | Or Same as the DEM (no reprojection) or a Specified CRS. The DEM is published in WGS 84; for any other CRS it is warped (bilinear) and the contours are made in that CRS. |
| Output folder | Folder | temporary | Empty means a temporary folder, which QGIS deletes when it closes. |
| Name | Text | — | Base name: <name>_DEM.tif and <name>_contours.gpkg. |
| Also add the DEM to the map | Boolean | — | Adds the clipped DEM with a pale elevation tint, below the vector layers. |
របៀបប្រើ
- Open KGA Irrigation Tools > Generate Contour for ROI.
- Choose the area. For a drawn area, click Draw rectangle or Draw polygon and draw on the map.
- Set the interval, the main-contour step, and the smoothing, symbology and label options.
- Pick an output folder, or leave it empty for a temporary one.
- Click Generate contours. Click Stop to cancel; nothing is added to the map.
លទ្ធផល
<name>_contours.gpkg— layercontours, in the output CRS, withID,ELEV(metres) andTYPE(mainorsub).<name>_DEM.tif— the clipped DEM, compressed, in the output CRS. Outside a drawn shape or layer boundary the DEM is NoData.<name>_hillshade.tif,<name>_slope.tif,<name>_aspect.tif— only the ones ticked, NoData −9999 (hillshade is Byte). Slope and aspect use the Horn method; for a DEM in degrees the horizontal scale is worked out from the latitude so the values match a projected CRS.- Layers made from Copernicus data carry its attribution in their metadata.
កំណត់សម្គាល់ និងដែនកំណត់
- Large areas. Above about 25 million DEM pixels (roughly 150 km square at 30 m) the tool asks before it starts, with a sterner warning above 150 million, and also when the output drive is short of space. A temporary output adds to the warning because it lands on the system drive. One request is limited to 700 million pixels.
- Too many levels. More than 20,000 levels — an interval of 0.1 m across a mountain range — is refused; the DEM is kept and the message says where.
- The Copernicus DEM is a surface model: it follows tree tops and buildings, not bare ground. Elevations are metres above the EGM2008 geoid.
- Attribution is required: Copernicus DEM © DLR e.V. 2010–2014 and © Airbus Defence and Space GmbH 2014–2018, provided under COPERNICUS by the European Union and ESA.
- Open sea has no tiles; an area entirely over open sea is reported as having nothing to contour.