Posts about Spatial

In my last post, I did a simple intro to foreign data wrappers in PostgreSQL. postgres_fdw is an extension available in Postgres core that allows you to issue queries against another Postgres database. It's just one of many foreign data wrappers

Raster data access from the spatial database is an important feature, and the coming release of PostGIS will make remote access more practical by allowing access to private cloud storage.

Previous versions could access rasters in public buckets, which is fine for writing blog posts

One theme of the 3.2 release is new analytical functionality in the raster module, and access to cloud-based rasters via the "out-db" option for rasters. Let's explore two new functions and exercise cloud raster support at the same time.

OpenTopography

My colleague Kat Batuigas recently wrote about using the powerful open-source QGIS desktop GIS to import data into PostGIS from an ArcGIS Feature Service. This is a great first step toward moving your geospatial stack onto the performant, open source platform provided by PostGIS. And there's no need to stop there! Crunchy Data

One of the less visible improvements coming in PostGIS 3.2 (via the GEOS 3.10 release) is a new algorithm for repairing invalid polygons and multipolygons.

Algorithms like polygon intersection, union and difference rely on guarantees that the structure of inputs follows certain rules. We call geometries that follow those rules "valid" and those that do not "invalid".

The rules are things like:

• Polygon rings should not cross themselves
• Polygon rings should not cross other rings
• Multipolygon components should neither touch nor overlap

A common situation in the spatial data world is having discrete measurements of a continuous variable. Every place in the world has a temperature, but there are only a finite number of thermometers: how should we reason about places without thermometers and how should we model temperature?

For many use cases, the right way to model a continuous spatial variable is a raster: a regularly spaced grid where each square in the grid contains a value of the variable. This works for temperature and precipitation; it works for elevation and slope; it even works for travel times and wayfinding.

For this blog post, we will build up a temperature surface for Washington State, using the discrete temperature measurements of a set of Department of Transportation (WSDoT) weather stations.

Getting the Data

Spatial indexes are used in PostGIS to quickly search for objects in space. Practically, this means very quickly answering questions of the form:

• "all the things inside this this" or
• "all the things near this other thing"

Because spatial objects are often quite large and complex (for example, coastlines commonly are defined with thousands of points), spatial indexes use "bounding boxes" as index and search keys:

• Bounding boxes are of a small, fixed size, only 4 floats for a 2D box; and,
• Bounding boxes are very inexpensive to compare to test things like containment.

We at Crunchy Data put as much development effort into improving GEOS as we do improving PostGIS proper, because the GEOS library is so central to much geospatial processing.

The GEOS library is a core piece of PostGIS. It is the library that provides all the "hard" computational geometry functionality:

• Intersections of geometry
• Unions of geometry
• Differences of geometry
• Buffers of geometry
• Geometry relationship evaluation

As a GIS newbie, I've been trying to use local open data for my own learning projects. I recently relocated to Tampa, Florida and was browsing through the City of Tampa open data portal and saw that they have a Public Art map

There are a lot of ways to load data into a PostgreSQL/PostGIS database and it's no different with spatial data. If you're new to PostGIS, you've come to the right place. In this blog post, I'll outline a few free, open source tools you can use for your spatial data import needs.

You can use a desktop GUI application like QGIS, and/or command-line utilities. If you want more flexibility, it's great to have both types in your toolkit.

I'll talk about importing to PostGIS within the context of vector data, since it's a much more common use case. It's possible to import raster data