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commit 0ee47d6711fcff0a93a8643adf7bbe0ce94c6e89
Author: buildbot <[email protected]>
AuthorDate: Fri Dec 16 20:55:39 2022 +0000
Automatic Site Publish by Buildbot
---
.../import-contour-into-postgis/index.html | 89 ++++++++++++++++------
output/sitemap.xml | 2 +-
2 files changed, 65 insertions(+), 26 deletions(-)
diff --git a/output/examples/import-contour-into-postgis/index.html
b/output/examples/import-contour-into-postgis/index.html
index d411ff8..fde89a9 100644
--- a/output/examples/import-contour-into-postgis/index.html
+++ b/output/examples/import-contour-into-postgis/index.html
@@ -3,7 +3,7 @@
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
- <title>Import contour lines data into PostGIS - Apache Baremaps</title>
+ <title>Contour Lines in Vector Tiles - Apache Baremaps</title>
<link rel="stylesheet" href="/assets/css/main.css">
</head>
@@ -94,56 +94,95 @@
</nav>
</div>
<article class="eight columns">
- <h1 id="import-contour-lines-data-into-postgis">Import contour
lines data into PostGIS</h1>
+ <h1 id="contour-lines-in-vector-tiles">Contour Lines in Vector
Tiles</h1>
-<p>In this tutorial, we demonstrate how to produce contours from a digital
elevation model (DEM).</p>
+<p>Contour lines are a key element in topographic maps, as they allow us to
+visualize the elevation of an area. In this tutorial, we will show you how
+to create contour lines from a digital elevation model (DEM) and display
+them using vector tiles.</p>
-<p>Notice that the following steps assume that the Apache Baremaps CLI and
PostGIS are <a
href="https://www.baremaps.com/getting-started/";>installed</a>.</p>
+<h2 id="prerequisites">Prerequisites</h2>
-<h2 id="dataset">Dataset</h2>
-
-<p>The approach consists in using the <a
href="https://gdal.org/programs/gdal_contour.html";><code
class="language-plaintext highlighter-rouge">gdal_contour</code></a> command.
-Therefore, start by installing <code class="language-plaintext
highlighter-rouge">gdal</code>:</p>
+<p>To follow this tutorial, you will need to have <code
class="language-plaintext highlighter-rouge">gdal</code> installed on your
+system. If you don’t have it already, you can install it by running the
+following command:</p>
<div class="language-bash highlighter-rouge"><div class="highlight"><pre
class="highlight"><code><span class="nb">sudo </span>apt-get <span
class="nb">install </span>gdal-bin
</code></pre></div></div>
-<p>The geotiff present in this directory comes from the <a
href="https://asterweb.jpl.nasa.gov/gdem.asp";>ASTER</a> dataset.
-We used the following command to reproject the geotiff in the desired
projection (e.g. WebMercator) before importing it in the database.</p>
+<h2 id="reprojecting-the-geotiff">Reprojecting the GeoTiff</h2>
+
+<p>We will be using the <a
href="https://asterweb.jpl.nasa.gov/gdem.asp";>ASTER</a> dataset
+for this example. The geotiff file provided in this tutorial is already in
+the desired projection (WebMercator), but in case you want to use a different
+geotiff file, you can use the gdalwarp command to reproject it. Here’s an
+example of how to do it:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre
class="highlight"><code>gdalwarp -rc \
-s_srs epsg:4326 -t_srs epsg:3857 \
-dstnodata 0 -of GTiff -co tiled=yes \
- examples/contour/liecthenstein-aster-dem-v2.tif \
- examples/contour/liecthenstein-aster-dem-v2-3857.tif
+ liecthenstein-aster-dem-v2.tif \
+ liecthenstein-aster-dem-v2-3857.tif
</code></pre></div></div>
-<h2 id="importing-the-data-into-postgis">Importing the data into PostGIS</h2>
+<h2 id="generating-the-contour-lines">Generating the Contour Lines</h2>
-<p>You can now import any GeoTiff DEM as contours in postgis.
-In the following command, the <code class="language-plaintext
highlighter-rouge">-nln</code> argument name the table that contains the data,
-the <code class="language-plaintext highlighter-rouge">-a</code> argument name
the column that contains the elevation,
-the <code class="language-plaintext highlighter-rouge">-i</code> argument
specifies the interval in meters at which contours are generated.</p>
+<p>Now that we have the GeoTiff in the desired projection,
+we can use the gdal_contour command to generate the contour lines.
+The <code class="language-plaintext highlighter-rouge">-a</code> argument
specifies the column that contains the elevation data,
+the <code class="language-plaintext highlighter-rouge">-i</code> argument
specifies the interval at which contours
+should be generated (in this case, we are using 10 meters),
+and the <code class="language-plaintext highlighter-rouge">-nln</code>
argument names the table that will contain the data.</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre
class="highlight"><code>gdal_contour \
-a elevation -nln aster_dem -i 10 \
-f PostgreSQL \
- examples/contour/liecthenstein-aster-dem-v2-3857.tif "PG:host=localhost
user=baremaps password=baremaps dbname=baremaps"
+ liecthenstein-aster-dem-v2-3857.tif "PG:host=localhost user=baremaps
password=baremaps dbname=baremaps"
</code></pre></div></div>
-<p>Some index can now be added to the database to improve performances.
-When available, a smoothing function such as <code class="language-plaintext
highlighter-rouge">ST_ChaikinSmoothing</code> can be used to improve rendering
of the contours.</p>
+<h2 id="improving-performance-with-indexes">Improving Performance with
Indexes</h2>
+
+<p>To improve the performance of the contour lines,
+we can add some indexes to the database.
+Here’s an example of how to create a <code class="language-plaintext
highlighter-rouge">SPGIST</code> index:</p>
<pre><code class="language-postgresql">DROP INDEX IF EXISTS aster_dem_gix;
-CREATE INDEX CONCURRENTLY IF NOT EXISTS aster_dem_gix ON aster_dem USING
SPGIST(wkb_geometry);
+CREATE INDEX IF NOT EXISTS aster_dem_gix ON aster_dem USING
SPGIST(wkb_geometry);
</code></pre>
-<h2 id="conclusion">Conclusion</h2>
+<h2 id="displaying-the-contour-lines">Displaying the Contour Lines</h2>
+
+<p>Finally, we can use Baremaps to display the contour lines in a web browser.
+To do this, run the following command:</p>
+
+<div class="language-bash highlighter-rouge"><div class="highlight"><pre
class="highlight"><code>baremaps map dev <span class="se">\</span>
+ <span class="nt">--database</span> <span
class="s1">'jdbc:postgresql://localhost:5432/baremaps?user=baremaps&password=baremaps'</span>
<span class="se">\</span>
+ <span class="nt">--tileset</span> <span class="s1">'tileset.json'</span>
<span class="se">\</span>
+ <span class="nt">--style</span> <span class="s1">'style.json'</span>
+</code></pre></div></div>
+
+<p>This will start the tile server and automatically reload the configuration
+files when you make changes. You can then preview the map in your
+web browser.</p>
+
+<h2 id="optional-smoothing-the-contour-lines">Optional: Smoothing the Contour
Lines</h2>
+
+<p>If you want to improve the rendering of the contour lines, you can use
+a smoothing function like ST_ChaikinSmoothing. This function takes
+a geometry as input and returns a smoothed version of that geometry.
+Here’s an example of how you could use it:</p>
+
+<pre><code class="language-postgresql">UPDATE aster_dem
+SET wkb_geometry = ST_ChaikinSmoothing(wkb_geometry, 0.1)
+</code></pre>
-<p>In this tutorial, we learnt how to import contour lines in PostGIS.</p>
+<p>Keep in mind that this step is optional and might not be necessary
depending
+on the quality of your input data. You can experiment with different
+smoothing parameters to find the best balance between smoothness and
+preservation of original features.</p>
-<p>Now that you have inserted the contour data into the PostGIS database, you
can use follow the <a href="/examples/serve-vector-tiles">Serve Vector Tiles
from PostGIS</a> example to serve
-your PostGIS data directly as Vector Tiles in a web application with live
reload capabilities.</p>
+<p>That’s it! You now know how to generate and display contour lines from
+a digital elevation model using vector tiles. Happy mapping!</p>
<p><a class="edit"
href="https://github.com/apache/incubator-baremaps-site/edit/main/examples/import-contour-into-postgis/index.md";><i
class="fas fa-edit"></i> Improve this page</a></p>
</article>
diff --git a/output/sitemap.xml b/output/sitemap.xml
index 646383c..e971d86 100644
--- a/output/sitemap.xml
+++ b/output/sitemap.xml
@@ -71,6 +71,6 @@
</url>
<url>
<loc>/assets/demo.html</loc>
-<lastmod>2022-12-12T14:33:41+00:00</lastmod>
+<lastmod>2022-12-16T20:55:36+00:00</lastmod>
</url>
</urlset>
