qgis_contours
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qgis_contours [2021/02/17 09:17] – bushwalking | qgis_contours [2024/05/13 08:08] (current) – Contour screenshot bushwalking | ||
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There are various contour extraction algorithms in QGIS, for example: | There are various contour extraction algorithms in QGIS, for example: | ||
* GDAL : Raster Extraction : Contour (same as Raster -> Extraction -> Contour...) | * GDAL : Raster Extraction : Contour (same as Raster -> Extraction -> Contour...) | ||
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+ | The two key fields are the //Input layer// (a DEM, ideally with sinks removed), and the //Interval between contour lines//. I typically use 10m or 5m for this. | ||
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+ | {{:: | ||
Below is an example of contours created without and with [[qgis_depressionless_dem|sink removal]]. The contours on the right have been derived from a DEM where the sinks (in yellow on the left) have been filled. | Below is an example of contours created without and with [[qgis_depressionless_dem|sink removal]]. The contours on the right have been derived from a DEM where the sinks (in yellow on the left) have been filled. | ||
{{: | {{: | ||
{{: | {{: | ||
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+ | It is worth noting that a [[qgis_depressionless_dem|depressionless DEM]] does not guarantee that there will be no contour sinks. A deep diagonal channel combined with a small contour interval can still cause sinks. {{:: | ||
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+ | See [[https:// | ||
===== Simplifying ===== | ===== Simplifying ===== | ||
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{{: | {{: | ||
- | Here is one approach, which involves adding a length attribute to each contour, and removing those that fall below a certain length. It may cause issues if you have short sections of contour near the edge of the map that you need. | + | Here is one approach, which involves adding a length attribute to each contour, and removing those that fall below a certain length. It may cause issues if you have short sections of contour near the edge of the map that you need. However, that shouldn' |
* Open Attribute Table (F6) | * Open Attribute Table (F6) |
qgis_contours.1613513842.txt.gz · Last modified: 2021/02/17 09:17 by bushwalking