Understanding Coordinate Systems in Surfer

A topic in which we receive many customer inquiries is coordinate systems. I recently reviewed the individual questions as they pertain to Surfer, and many users are confused about where to change the coordinate system information, what to set it to, or what order to perform the steps. To shed some light on this very important component of map making, this blog will address these questions.

I recently had a question where a user needed to convert the XY coordinates of the map from lat/lon (degrees) into meters, so that they could add a profile to the map showing meters as the Distance units instead of degrees. 

Before the map can be converted into a new coordinate system, each layer in the map needs a coordinate system assigned (or “set”) to it. That way, Surfer knows how to convert each layer from its source coordinate system to the target system specified for the map.

The coordinate system assigned to the layer is the source coordinate system for that layer (the coordinate system of the file used to create that layer). The coordinate system for the map is the target coordinate system and can be anything you want. Each layer will be individually transformed on-the-fly from their respective source coordinate systems to the target coordinate system of the map and displayed in the plot window in the target coordinate system.

For example, the map above has multiple layers in it (a contour layer and an image layer). The steps to follow to convert the coordinate system of the map from lat/lon to another coordinate system (e.g. UTM) are:

1. Click File | Open and open Unprojected.srf .  This is a Surfer 13 project file. The coordinates for the map are lat/lon (you can see this on the axis labels); however, the layers in the file do not have any coordinate system specified. The units may be lat/lon, but Surfer doesn’t know they are lat/lon.
2. The first step is to set the source coordinate systems for each layer. Let’s start with the Contours layer.
   1. Select the Contours layer in the Object Manager.
   2. In the Property Manager, click the Coordinate System tab.
   3. Click the Set button.
   4. Select Predefined | Geographic (lat/lon) | World Geodetic System 1984. 
   5. Click the Add to Favorites button (so you don’t have to navigate to this system again)
   6. Click OK.
3. Set the source coordinate system for the other layer in the map.
   1. Select the Image layer in the Object Manager.
   2. In the Property Manager, click the Coordinate System tab.
   3. Click the Set button.
   4. Select World Geodetic System 1984 under Favorites.
   5. Click OK. Now both layers should have a source coordinate system assigned to them. Again, this is the coordinate system for the grid or data file used to create the layer (not what you eventually want it to be displayed in).
4. Now let's change the target coordinate system for the map.
   1. Select the Map in the Object Manager.
   2. In the Property Manager, click the Coordinate System tab.
   3. Click the Change button.
   4. Since we want the XY units to be in meters (to match the elevation units), we can use one of the UTM coordinate systems. Select Predefined | Projected Systems | UTM | North America | North America NAD83 UTM zone 10N.
   5. Click OK.
5. Once you click OK, each of the layers have been projected from geographic lat/lon to UTM, and the UTM units are displayed on the X and Y axes.
6. Now that the map has been converted and is in meters, you can add the profile by clicking Map | Add | Profile, and clicking on the map where you want the section line placed. The distance units now are measurable and you can set the scaling and vertical exaggeration.
7. If you would like to add the lat/lon values back next to your axes for display purposes, you can do so by adding a graticule (Map | Add | Graticule).

In some cases, e.g. calculating volumes or blanking a grid, you may need to actually convert the coordinate system of the grid file or boundary file itself and not just the map display.  For information on converting the coordinate systems of source data or grid files, please see our newsletter article Converting the Coordinate System of Data, Image, Vector, and Grid Files in Surfer. If you still have any questions about coordinate system or how to manage them in Surfer, please contact us at surfersupport@goldensoftware.com.

Other resources that might be of use:

1. Videos:
   1. Webinar: Frequently Asked Questions of Surfer 12 (part 2 at 12:00, Do I need to set the coordinate system for my map?)
   2. Training Video: Setting and Changing Coordinate Systems for Maps - Surfer 12
2. KB articles:
   1. Converting the Coordinate System of Data, Image, Vector, and Grid Files in Surfer
   2. Why would I want to set the coordinate system for a map or layer?
   3. How can I use different coordinate systems in the same map?
   4. Do I need to specify a coordinate system for every map layer in Surfer?
   5. How can I convert the coordinate system of a grid file (e.g. from Lat/Long into feet or meters)?
   6. How can I convert the coordinate system of raw data, such as from UTM to Lat/Long?
   7. How do I know if Surfer supports my coordinate system?
   8. How can I convert the coordinate system of a BLN file?
3. Help. Click Help | Contents from within Surfer, and on the Contents page, expand the Surfer 14 | Coordinate Systems book. Under this book are many references to help understand projections and datums. A list of references is given on the Projection References page and provides many good resources that are available either online or in printed documentation.