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Maps and Map Layers in Surfer Mapping Software: The Source Coordinate System vs. the Target Coordinate System

Since Surfer 10, users have been able to create maps using layers that contain data from different coordinate systems and reproject the layers to the desired coordinate system on the fly. This valuable feature has streamlined workflows, eliminating the need to transform all data to the same coordinate system before using it to create multi-layered maps. For an example, see the sample file CoordinateSystems.srf, located by default at C:\\Program Files\\Golden Software\\Surfer 12\\Samples. Let's take a look at this powerful component of Surfer's 3D Mapping software!

Know your data

If your data file has coordinate system information embedded, or if Surfer finds an associated location reference file (for example, a PRJ file), Surfer will automatically assign the coordinate system for the map layer when it is created. If no location information is found, or if location information is recognized, but is incorrect, the coordinate system can be manually assigned. It is important to know the coordinate system of the data and where in the world the data is located. An improperly assigned coordinate system can result in undesired results.

Source coordinate system vs. target coordinate system

There are two coordinate systems to consider when working with maps and map layers in Surfer's mapping software: the source coordinate system and the target coordinate system. The source coordinate system is the coordinate system of the data, and the target coordinate system is the coordinate system in which the map is displayed. The two coordinate systems may be the same, or may be different, for a map.

Source coordinate system

The coordinate system of the data used to create a map layer is the source coordinate system. When a map layer is selected, the source coordinate system is displayed on the Coordinate System page of the Property Manager. If Surfer is unable to find location information for the data, Unreferenced local system is displayed for the Name. In this case, or if the location information is incorrect, you can set the source coordinate system for the layer. If the source coordinate system is incorrectly specified, you may see a blob, a mess of black lines, or your map may disappear or locate incorrectly when overlaying it with other data.

The image below shows what the Coordinate System page of the Property Manager looks like for a map layer before and after specifying a source coordinate system. Note that the page says Source Coordinate System, and the button reads Set.

Source ba

Coordinate System page for a map layer before and after assigning a source coordinate system.

To specify a source coordinate system for a layer:

  1. In the Object Manager, select the map layer, such as a Contours or Post layer.
  2. On the Coordinate System page of the Property Manager, click the Set button.
  3. In the Assign Coordinate System dialog, navigate to and select the coordinate system in which the source data exists.
  4. Click OK.

The Property Manager updates with the newly assigned coordinate system.

Target coordinate system

The coordinate system in which the map is displayed is the target coordinate system. This may be different from (or it may be the same as) the source coordinate system. When the map itself is selected, the target coordinate system is displayed in the Property Manager. If no target coordinate system is defined, Unreferenced local system is displayed for the Name. Change the target coordinate system to change the coordinate system in which the map is displayed, and change the values of the coordinates displayed on the axes.

The image below shows what the Coordinate System page of the Property Manager looks like for a map before and after specifying a target coordinate system. Note that the page says Target Coordinate System, and the button reads Change. Additionally, the image above and the image below were taken from the same map. Note that the source coordinate system is different from the target coordinate system.

Target ba

Coordinate System page for a map before and after assigning a target coordinate system.

To specify a target coordinate system for a map:

  1. In the Object Manager, select the Map.
  2. On the Coordinate System page of the Property Manager, click the Change button.
  3. In the Assign Coordinate System dialog, navigate to and select the coordinate system in which you want the map to be displayed.
  4. Click OK.

The Property Manager updates with the newly assigned coordinate system, and the values displayed on the axes update to reflect the new coordinate system.

When and why assign a coordinate system?

There are a few cases in which a coordinate system is necessary for a map or a map layer:

  1. If the data sets for the layers are in different coordinate systems, each layer must have a source coordinate system assigned for the layers to locate and overlay properly.
  2. If you want to change the coordinate system of the map, each layer must have the appropriate source coordinate assigned before the target coordinate system of the map is changed for a proper display.
  3. If you want to export the map to a referenced file, such as a KML or GeoTIFF file, a coordinate system is necessary so the map exports correctly. If the data for each map layer is in the same coordinate system as the map, each layer does not need the coordinate system to be set, but the coordinate system of the map must be specified. If you specify the coordinate system of the map without specifying it for the layers, you may receive a warning that the layers cannot be converted to the map's target coordinate system. Because all the data is in the same coordinate system, no transformation is really necessary. Just click OK to close the warning.

To see this feature in action, take a look at our training video Setting and Changing Coordinate Systems for Maps. Additionally, the information contained in this article (and more) can be found in various Surfer Knowledge Base articles.

Do you have any questions about this post? Do you have an idea for a blog post or have a topic you'd like to see featured? Let me know! Leave a comment, or send an email to jennifer@goldensoftware.com.

 

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Wednesday, 22 November 2017

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