Transform - Tiles: Path

The Path template appears in the template list when a raster tile field, of type Tile, has been picked in the Transform pane.  The template computes closest path analytics, similar to the Distance tools in ESRI's Spatial Analyst toolset.   


The template provides nine basic path computation operations, which can be selected within the Path template by choosing the desired combination of three different Path type options and three different Output type options.


This topic is a quick summary:  Path template operations are covered in the extensive Raster Paths topic.



Template options that compute closest path analytics, similar to the Distance tools in ESRI's Spatial Analyst toolset.  The transform provides three basic Path types. Each of those can compute results in three different Output types, providing a total of nine different combinations of Path type and Output type.  


The Path transform should be launched with the focus on an image layer in a map that also contains a vector drawing layer that provides points for starting locations.  Points used in path computations can be restricted to only those selected, using the Start from selection only check box.  The Path transform allows a choice of Channel to use in multichannel images.  


Path type options:


  • cost - Measure distance through a lowest cost pixel-to-pixel route, taking the value of each pixel as its cost, which might not be direct, from each pixel to the closest point.  Avoids pixels with NULL values.  Checking the Use equal costs box (the default) uses the same cost for all pixels.  The overall length of the path is thus the cost of the path, with the shortest pixel-to-pixel path being the least cost.  Unchecking the Use equal costs box counts the value of each pixel as the cost of that pixel, and adds up the costs of pixels that the path goes through to get the total cost of the path.    
  • cost for slope - First calculate slopes for the raster, and then compute lowest-cost path distances using the slope for each pixel where going downhill on a slope has lower cost than going uphill.
  • Euclidean - Measure distance by simple, straight line, Euclidean distance from each pixel to the closest point.   When the Use barriers box is checked, Euclidean templates will find the shortest route using straight line segments which avoids NULL pixels, called barriers, .


Output type options:


  • direction - Report the direction from the pixel to the closest point.
  • distance - Report the distance from the pixel to the closest point.
  • value - (Formerly known as Source Z value) Fill each pixel with the same value, either taken from a field value for the closest point, or with a sequential value.


Value options:


  • (sequential values) - Assign a sequential integer value (zero based counting) to pixels closest to each point.  If there are three points, all pixels closest to the first point will be assigned the value 0, those pixels closest to the next point will be assigned a value of 1, and those pixels closest to the third point will be assigned a value of 2.
  • <choose a field> - Choose a field from which the value will be assigned to all pixels associated with that point as a closest point.


Parameters for cost for slope:


  • Min slope, Max slope - Allowed minimum and maximum slopes in degrees.   The path will be routed around any pixels that have a slope value less than the minimum slope or greater than the maximum slope.  The slope of a given pixel can be interpreted as a negative slope or a positive slope depending on the direction we are travelling.  The default values of -90 and 90 mean to use pixels with all slopes.  A more realistic scenario is not to walk off a cliff (-90) or to attempt to scale a cliff (90).   We can specify the minimum and maximum slopes acceptable, such as not descending by any slopes steeper than -30 degrees, or ascending by any slopes greater than 30 degrees.  
  • Min slope costMax slope cost - The cost of a pixel in the path, based on the slope of the pixel and the Min cost and Max cost values.   The Min slope cost value is the cost for pixels that have the specified Min slope value of slope.   The Max slope cost value is the cost for pixels that have the specified Max slope value of slope.  The costs of all other pixels are interpolated, based on their slopes, between the Min slope cost and Max slope cost values. The default value of 0 for Min slope cost in most cases will be replaced by 1, so that all pixels have at least some cost.   The default value of 2 for Max slope cost in most cases will be replaced by a larger number, such as 100, to allow for a greater range of values between minimum and maximum costs.
  • Flat Cost - The per pixel cost of a path over flat, that is, zero slope, terrain.  It makes sense to make this about halfway between the Min cost and Max cost values.

  • Reverse path - Paths in cost for slope operations are computed by default from each pixel in the raster to the source point.  Checking the Reverse path box switches directionality to compute paths from source points to each raster pixel in their domain.   The direction matters because a downward slope path is shorter, that is, lower cost, than the reverse upward path.


Launch the template by choosing a Tile field and then double-clicking the Path template.  When the template launches we can specify options.



 See the Raster Paths topic for a detailed discussion and examples.    



See Also

Raster Paths


Transform Pane


Transform Reference


Transform - Tiles