Postgis examples

We will be using mostly Boston, Massachusetts data to provide mapping and spatial database examples. If you have some thoughts or comments on what you would like to see covered on this site, drop us a line on our Feed Back page.

In a nutshell it adds spatial functions such as distance, area, union, intersection, and specialty geometry data types to the database. As of this writing PostGIS 2. Noteable features in this release:. The PostGIS windows 2. In the bundle you will also find:. We will assume a windows environment for this tutorial, but most of the tutorial will apply to other supported platforms such as Linux, Unix, BSD, Mac etc.

We will not go into too much detail here since the install wizard at least the windows one is pretty good. Below are the basic steps. The create spatial database checkbox is optional, and we generally uncheck it. It creates a spatial database for you to experiment with and has all the extensions packaged with PostGIS Bundle pre-installed. For those of you who want to try experimental builds -- e. We have experimental Windows builds made weekly or as frequently as anything interesting happens in the PostGIS code base.

You can use something like psql or the pgAdmin query window to create a database and spatially enable your database. This is the way to go if you have only a terminal interface to your db or you have a butt load of extensions you want to enable. Your psql steps would look something like this:. To install a bunch of extensions, just open up the pgAdmin SQL Query window which we'll cover shortly or psql and run this including only the extensions you want.

If you are a newbie or not sure what extensions you want, it's best just to use that tool to create a new database and look at the menu of extensions you have available to you. This will allow any person logging locally to the computer that PostgreSQL is installed on to access all databases without a password.

Note you can add additional lines to this file or remove lines to allow or block certain ip ranges. The lines highest in the file take precedence. So for example if you wanted to allow all users logging in access as long as they successfully authenticate with an md5 password, then you can add the line host all all 0.

If it is below, you will still be able to connect locally without a password but non-local connections will need a valid username and password.Databases are useful for long-term data storage, rather than short-term data transfers, so the key operations are getting data into and out of that storage. All of the activities above involve not only transforming the data into the correct format, but also transforming the data into the correct schema data model. All of these examples are also applicable to using the PostgreSQL format.

The final article works with PostgreSQL so you can see the difference between a spatial and a non-spatial tabular database. When working with FME and databases, it is important to clarify some of the basic database terms used by FME, as they may differ from what is used in a particular database package.

postgis examples

The schema is similar to the term data model; however, FME schema does not generally include data model relationships. A mathematical system that uses one or more values to determine the position of points on the earth, these values are typically displayed as x, y and z values.

This example takes coordinate information stored in latitude and longitude table columns, converts them to points, and joins the points together to form a walking path. This tutorial can also be completed using the PostGIS reader. Tutorial: Updating Databases. Tutorial: Let the Database Do the Work. Attachments: Up to 10 attachments including images can be used with a maximum of 4. Converting from PostGIS.

Performing spatial queries on database tables using the FeatureReader. FME is loading features with invalid geometries into my Database. Powered by AnswerHub. FME is Here! See What's New safe. Forums Knowledge Base Ideas Documentation. New Question New Idea. Sign in. Export to PDF. Article created with FME Desktop Add comment. Follow this article.Seemingly simple questions like how many Starbucks are in New York or how many elementary schools are in my neighborhood can be answered by a simple GIS query.

About PostGIS

PostGIS is a spatial extension of the Postgresql relational database. The PostGIS extension has many spatial queries built in that can answer different types of question.

The function determines rather geometry A is completely inside geometry B. The function returns True if that is the case. This can be used to count how many geometries are inside a large geometry.

Step-by-Step Python and Postgres Tutorial with psycopg2

Chicago data portal provides spatial data about the city. This example will determine how many bicycle racks are in each neighborhood. The bicycle racks and neighborhoods tables are already imported in the PostGIS database. You can find the steps on how to download bicycle racks and neigborhood in the he perlinks.

The map shows bicycle racks scatter across the city in each neighborhood. It is impractical and will be incorrect to count them all by hands. The fastest way is to write a database query that will count them for us. This guide assumes you have some basic knowledge writing SQL queries. First, we will construct a working SQL query in pgAdmin that calculates the number of bicycle racks within each neighborhood.

To do that open up pgAdmin in your browser. You can learn more about how to set up a local PostGIS database here. Once you have pgAdmin open, select the database that contains your data.

postgis examples

Next, click on Tools and then click on Query Tool. This will bring up an empty text box tab where you can start writing your query. The next step of the process is constructing the SQL query. The following query selects the name of the neighborhood and counts how many racks are in each neighborhood. First, the query joins the bicycle rack with the neighborhood if the rack is within the neighborhood.

Next, the query groups the neighborhoods together and count how many bicycle racks are within each. Finally, we can order by the number racks in a descending order. Enter the above query in the text box, then hit F5, or click on the lightning button to run the query.With PostGIS you can store geospatial data and perform spatial queries on a postgres database. Unlike the default datatypes on a normal postgres database, spatial data has to be handled differently. The queries you can perform on a spatial database are usually defined by bounding-boxes in 2 or 3 dimensions.

To store, index and handle these datatypes postGIS uses a concept called R-Treeswich is not part of the default postgres-installation. In this example we will set up a geospatial database, import data from 2 different sources, and view the results in an application called QGIS. This guide is explicitly written for linux-machines, if you operate on another platform, some commands or paths might not work as expected.

In order to view the imported data we will use an application called QGIS. If you don't have this application, please install it firstif you like to use another viewer or geo-application like ArcGIS you can skip installing QGIS. Please Download the appropriate files frome the linked locations. You should also take a look at the Metadata-section of the material, since it gives you information on what coordinate reference system these files use.

To start, create a working folder "nycgis", copy the downloaded files to the location and unzip the archives. When working with geo data it is of vital importance, to know the coordinate reference system CRS of your source data, and of your final output data.

Lets assume we want to use a different CRS in our database. This can have different reasons, we might want to work with a web-based geo application on the database for example.

To convert the coordinate systems we use a tool called ogr2ogr wich is part of the GDAL package. In the working folder, we first create 2 folders representing the reprojected data, and then convert our data. Notice that we only use the file called: "ad. The syntax of the ogr2ogr -command is as follows:. We now have 2 shapefiles, projected in the correct CRS. In order to use the data in our database, we must convert the shapefiles to sql-statemens. For this we use a tool called shp2pgsql. In the working directory run the following commands:.In addition, PostGIS supports a raster type no standards exist to followand a topology model following an early draft ISO standard for topology that has not been published as yet.

Both representations include information about the type of the object and the coordinates that form the object.

Your First Steps With the Geography Data Type

Examples of the text representations WKT of the spatial objects of the features are as follows:. The SRID is required when creating spatial objects for insertion into the database. Examples of the text representations EWKT of the extended spatial objects of the features are as follows.

The "canonical forms" of a PostgreSQL type are the representations you get with a simple query without any function call and the one which is guaranteed to be accepted with a simple insert, update or copy.

For the postgis 'geometry' type these are:. The well-known text extensions are not yet fully supported. Examples of some simple curved geometries are shown below:. A single segment required three points, the start and end points first and third and any other point on the arc. The exception to this is for a closed circle, where the start and end points are the same. In this case the second point MUST be the center of the arc, ie the opposite side of the circle.

This means that a valid circular string must have an odd number of points greated than 1. A compound curve is a single, continuous curve that has both curved circular segments and linear segments. That means that in addition to having well-formed components, the end point of every component except the last must be coincident with the start point of the following component.

The difference is that a ring can take the form of a circular string, linear string or compound string. PostGIS prior to 1. All floating point comparisons within the SQL-MM implementation are performed to a specified tolerance, currently 1E Geographic coordinates are spherical coordinates expressed in angular units degrees.

The basis for the PostGIS geometry type is a plane. The shortest path between two points on the plane is a straight line.

postgis examples

That means calculations on geometries areas, distances, lengths, intersections, etc can be calculated using cartesian mathematics and straight line vectors. The basis for the PostGIS geographic type is a sphere. The shortest path between two points on the sphere is a great circle arc. That means that calculations on geographies areas, distances, lengths, intersections, etc must be calculated on the sphere, using more complicated mathematics.

For more accurate measurements, the calculations must take the actual spheroidal shape of the world into account, and the mathematics becomes very complicated indeed.

Because the underlying mathematics is much more complicated, there are fewer functions defined for the geography type than for the geometry type. Over time, as new algorithms are added, the capabilities of the geography type will expand.

It uses a new data type called geography. None of the GEOS functions support this new type. As a workaround one can convert back and forth between geometry and geography types. The new geography type uses the PostgreSQL 8. All the standard OGC formats except for curves are supported. The geography type only supports the simplest of simple features.

Standard geometry type data will autocast to geography if it is of SRID Note that the location column has type GEOGRAPHY and that geography type supports two optional modifier: a type modifier that restricts the kind of shapes and dimensions allowed in the column; an SRID modifier that restricts the coordinate reference identifier to a particular number.

The modifier also supports dimensionality restrictions through suffixes: Z, M and ZM. Query and measurement functions use units of meters. So distance parameters should be expressed in meters, and return values should be expected in meters or square meters for areas.It adds support for geographic objects allowing location queries to be run in SQL. Refer to License FAQ for more information. Follow postgis. Best served with PostgreSQL As of PostGIS 2.

All function calls within the extension are now schema qualified. While this change fixed some issues with database restore, it created the issue of if you installed PostGIS in a schema other than the one you wanted to it is not intuitive how to move it to a different schema. Luckily there is a way to do this. For this exercise, I will install PostGIS in the default schema and then demonstrate how to move it into another schema location. Vanguard Appraisals is new to the GIS world.

We do mass property appraisal for entire county and city jurisdictions, and we develop software to collect, price and maintain values. We also host assessment data online so that homeowners can search and find property information much simpler from the comfort of their own home. Should you upgrade now? This release works with PostgreSQL 9.

Read More… More News…. JulValmiera, Latvia.Geographical applications are everywhere: GPS and sat nav systems, maps, get-a-taxi apps, real estate portals, etc.

PostGIS ST_Within example and the Python equivalent

Behind each of them is a spatial database storing geographical data, and supporting spatial queries. In this article, we will introduce PostGIS, the main open-source spatial database manager. It adds support for geographic objects, allowing location queries to be run in SQL.

Both allow the storage of points in a table, as well as other more complex shapes like lines a line is defined by two pointsmultipoint lines defined by N pointspolygons defined by a closed multipoint lineand points with a specific altitude defined by a third coordinate.

This extender also offers a set of spatial functions for distance calculation, area calculation, intersection, and inclusion, among many others. All these new data types and functions can be used in combination with regular relational data in SQL, increasing the power of queries. In this article, we will cover the first steps of using PostGIS by exploring features like the geography data type and some spatial functions such as distance, area and intersection.

This table will have the following schema:.

postgis examples

First, we will insert some relational data for a few art masterworks. Note that the latitude and longitude fields are still float numbers and are being stored as regular relational data, not spatial. This returns a geography data point, as we see in the following SQL statement:. After this update, we have our first geography data points in the database. We have two items to clarify here.

The first is that when we used the geography data type, we omitted to mention the category. We need some software to interpret their meaning; for example, if we use QGIS we can show the four geography points on a map. Have a look at the results in the following screenshot:. The previous paragraph opens the door to a central concept in the spatial database standard. Every spatial element like a point, line or polygon can be expressed or defined using two different formats:.

As we saw in the previous example, every geography element in PostGIS is represented internally as a string of hexadecimal digits in WKB format. Obviously, this is really difficult for humans to understand.

Some examples of WKTs are:. This is the inverse function; given a WKT format, it returns the associated geography. The basis for the PostGIS geometry data type is a plane. The shortest path between two points on a plane is a straight line.

That means calculations for geometries areas, distances, lengths, intersections, etc. On the other hand, the basis for the PostGIS geography data type is a sphere. The shortest path between two points on the sphere is a great circle arc.

That means that calculations on geographies areas, distances, lengths, intersections, etc. Moreover, the earth is not a perfect sphere, so calculations must consider the world as a spheroidal shape Too complicated!

The following SQL query calculates the distance between our four masterworks, showing all possible combinations. By definition, distance results in PostGIS are expressed as meters.


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