How to generate contour lines in PostGIS intronautics?

How to generate contour lines in PostGIS intronautics?

Now that we have the points on each cell’s side that belongs to a contour line, let’s generate the segments that leave a different bucket value at each side of it. Take into account that there are 27 possible results (image from Wikipedia):

How to generate contour lines from scatter data?

There’s a bunch of different ways to generate contour lines [1] from scatter data, each of them based on different interpolation algorithms. Like KNN [2], IDW [3] or kriging-flavoured methods [4]. (image from Wikipedia)

Which is the best method for contour lines?

But, for performance sake, I’m going to use here a method derived from marching squares [5] method, that fits irregularly scattered data points: meandering triangles [6]. The algorithm is pretty clearly described in the linked reference, so let’s go straight to the code.

How to create a polygonal grid in PostGIS?

However, if you want to create a regular polygonal grid, you can use the ST_PixelAsCentroids function to convert each raster to a point and a value, and then use ST_Expand to convert this point back to a square representing the size of your raster coverage, and then feed these to the function in your link above.

How are elevation contours created by the USGS?

Service Description: The USGS Elevation Contours service from The National Map displays contours generated for the United States at various scales. Small-scale contours were created by USGS TNM from 1 arc-second data with 100-meter contours, and are visible at 1:600,000 and smaller scales.

How often are the contours of a map updated?

Large scale contours are updated every quarter, and are created by USGS TNM for the 7.5′ 1:24,000-scale US Topo digital map series. These contours are derived from 1/3 arc-second or better resolution data, and are visible at scales 1:50,000 and larger.

How to create contour shapefile with GDAL and PostGIS?

Using gdal_contour, I created a single contour shapefile at 10 meters interval where the elevation value is in the “elev” column. 4. To add the new shapefile to my existing PosGIS DB, I used a two step process where your first convert the shapefile into a sql file using shp2psql and then with psql, add the the sql file as a new table.

How do you make contour lines from DEM tiles?

1. I downloaded DEM tiles from the SRTM CGIAR website ( http://srtm.csi.cgiar.org/Index.asp ). 2. In order to generate the contour for all the DEM files, I created a VRT to “stitch” all the DEM tiles. This way, I get a continuous contour line along the edges of each DEM tile. 3.

How to create contour lines with Aster DEM data to show?

My job was to transform those into a form that is usable in our locator maps. Another way to show the shape of a mountain on a map are contour lines. These lines appear after equal elevation gains, so after e.g. 1100m, 1200m, etc.

How to dem query elevation data in PostGIS-geographic?

ST_SetSRID () is to build your points in the same coordinate system as the rasters. Just do: to know the right number of the coordinate system and replace ‘12345’ with that number. ST_Intersects (rast, geom) takes avantage of the indexes and make sure the query will return quite fast.