Assign NoData outside of Alpha Shape

Assign NoData to grid nodes outside of an alpha shape directly in the Assign NoData, Grid Data, and Grid from Contours dialogs! The Alpha Shape allows you to create a tight polygon boundary around your data points, much like the existing Convex hull option. The Alpha shape can create a concave or convex hull around data points, you control on how tight the polygon clings around the data limits. 

Create an alpha shape and use it to assign NoData values when gridding your data.

Alpha shapes can be applied to a surface in the following ways:

1. Created directly in the Grid Data dialog. Use this option if you are starting out with XYZ data points listed in a text file (i.e. DAT, XLSX, CSV).
   ** You can choose whether to create the shape in the dialog, or upload an existing alpha shape. 
   
   
2. Created directly in the Grid from Contours dialogs during grid creation. Use this option if you have contour lines in a vector file format (i.e. DXF, SHP). 
   ** You can choose whether to create the shape in the dialog, or upload an existing alpha shape.
    
3. Created in a Base(vector) layer and loaded into the Assign NoData dialog and applied to an existing grid. Use this option if you have created an Alpha Shape in a base map or saved in a vector file format and you'd like to apply this specific border to an existing grid file. 
   ** A pre-existing alpha shape is required. See Introducing the Alpha Shape for more information. 

See instructions for all methods below: 

1. Created directly in the Grid Data dialog: 

1. Click Home | Grid Data | Grid Data. 
   
2. Import the data file and fill out the Grid Data dialog as normal. Learn more in the knowledge base article Gridding Data in Surfer. 
3. Click Skip to End >> or click Next> until the Grid Data - Output page is showing. 
4. Change the Assign NoData outside of field to Alpha Shape. 
5. Change the Alpha value field if desired. The larger the value the more convex the polygon will be, and the smaller the number the move concave the polygon will be. 
6. Alternatively, if you created an alpha shape in a Base(vector) layer or vector file, import this file into the Assign NoData section. 

2. Created directly in the Grid from Contours dialog:

1. Click Grids | New Grid | Grid from Contours. 
2. Import the data file and fill out the dialog normally. Learn more about the Grid from Contours dialog here. 
3. In the Options section, change the Assign NoData outside of field to Alpha Shape. 
4. Update the Alpha value as needed. The larger the value the more convex the polygon will be, and the smaller the number the move concave the polygon will be. 

3. Created in a Base(vector) layer and loaded into the Assign NoData dialog and applied to an existing grid: 

1. Create your Alpha Shape on existing XYZ data points in a text file. See Introducing the Alpha Shape for specific steps. 
2. Create your grid if you haven't already. Instructions can be found in the knowledge base article Gridding Data in Surfer or the Surfer Gridding Training Video. 
3. Click Grids | Edit | Assign NoData. 
4. Browse to or select your grid in the Input Grid section. 
5. Browse to or select an Alpha shape contained in an open Base(vector) layer. 
6. Choose to Assign NoData Inside, Outside, or Mixed. Learn more about the other options in this dialog In Surfer's Help or the Surfer Converting Areas in a Grid File to NoData Training Video. 
7. Enter a name for the new Output grid and choose whether you'd like to open the new grid as a map or new layer and click OK. 

Video Tutorial: