Once your landscape is selected, use a shape or shapefile to indicate the location and pattern of ignition on the landscape.
You must select your landscape prior to selecting an Ignition file. Available files are limited to:
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Shapes you’ve created in IFTDSS or shapefiles you’ve uploaded. Points, lines, and polygons are all available as ignitions.
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Shapes or shapefiles that intersect your landscape, or the buffered area surrounding it.
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A single shape or shapefile. The file may be single or multipart.
Important! Ignitions and barriers must be at least one cell width away from each other or the model run will fail.
Once a shape or shapefile is selected for the ignition input, it may not be used for the barrier input.
Using Polygons
Polygons may be used to represent ignitions. Be aware of the information below to successfully model using this ignition type:
Important! To avoid run failure or misinterpretation when using polygons:
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Be aware MTT Fire Spread treats the area within the polygon as non-burnable, fire is not permitted to burn inward.
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Do not use ignition files that land completely in unburnable fuels or within a barrier, these will cause a run failure.
Resolution and Raster Conversion
The Minimum Travel Time Fire Spread (MTT) model is a raster based model that converts ignition and barrier vectors to rasters prior to the model running. Point and line ignitions will default to the same width as the cell resolution of your landscape.
The images below show a before (image A) and after (image B) example of lines and polygons being converted to raster format.
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Image A shows two vectors, a line used for ignition (orange) and a polygon used for a barrier (green), that were entered as inputs for a MTT run.
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Image B shows those same inputs after they have been converted to grid format for running MTT.
Creating an Ignition While Using the MTT Fire Spread Interface
In Split Screen, you may create points, lines, and polygons at anytime in the map interface and these features will automatically become available in the drop-down menus for the Ignition and Barrier inputs. This includes creating a shape, uploading a shapefile, creating a shapefile subset from the Layer List widget, or from the Attribute Table. Split Screen is the default display mode for MTT.