Résumé
Creates a raster object that can be used in Python scripting or in a Map Algebra expression. A raster object is a variable that references a raster dataset.
A raster object can be created in two ways, by supplying the path to an existing raster on disk, or it can be the result of any Map Algebra statement that results in a raster output.
Discussion
The raster object created from existing data can be used in subsequent Map Algebra expressions and will have all the associated raster properties and methods.
# out_raster is a resultant raster object
out_raster = Raster("c:/data/inraster")
Any tool or operator (see Working with operators in Map Algebra) that produces an output raster to the left of the equal sign creates a raster object. For example, in the following expression, out_raster is a raster object.
out_raster = Slope("inelevation")
When a raster object is returned from a Map Algebra expression, by default, the object (the variable and associated dataset) is temporary.
The temporary dataset associated with a raster object can become permanent with the following mechanisms:
- By calling the save method on the raster object.
- Call Make Permanent by right-clicking the layer with an associated raster object in the TOC and specifying an output name.
- Saving the map project (.mxd, .3dd, and so on) that contains any layers with associated raster objects.
In case 3, the dataset referenced by the raster object will automatically be permanently saved to disk with a default name.
If the referenced raster is not made permanent by any of the three cases above, the variable and the referenced raster dataset will be deleted when the variable goes out of scope, such as when a stand-alone script is completed or ArcGIS is closed. When a raster object references permanent data on disk, the data is not deleted.
Certain operators exist in both Map Algebra and in Python. If you want an operator to work on rasters (as opposed to scalars), the input rasters must be cast as a raster object by calling the Raster class constructor: Raster("inRaster").
# The plus operator (available with Spatial Analyst) is used on the input
# rasters creating an output raster object
out_raster = Raster("input1") + Raster("input2")
# The Python plus operator is used on numbers creating a scalar variable
out_var = 4 + 7
# When there is a mix of rasters with numbers the Spatial Analyst
# operator is used creating an output raster object
out_raster = Raster("input") + 10
Certain properties associated with the raster object are only available if the referenced raster dataset is permanent. When the referenced raster dataset is temporary, these properties will be assigned None. The affected properties are catalogPath, compressionType, format, hasRAT, name, and path.
Once permanent, the referenced raster dataset cannot return to the temporary state.
Syntaxe
Raster (inRaster)
| Paramètre | Explication | Type de données |
inRaster [inRaster,...] | The input raster dataset or list of raster datasets. | Raster |
Propriétés
| Propriété | Explication | Type de données |
| bandCount (Lecture seule) | The number of bands in the referenced raster dataset. | Integer |
| catalogPath (Lecture seule) | The full path and the name of the referenced raster dataset. | String |
| compressionType (Lecture seule) | The compression type. The following are the available types:
| String |
| extent (Lecture seule) | The extent of the referenced raster dataset. | Extent |
| format (Lecture seule) | The raster format.
| String |
| hasRAT (Lecture/écriture) | Identifies whether there is an associated attribute table: True if an attribute table exists, or False if no attribute table exists. | Boolean |
| height (Lecture seule) | The number of rows. | Integer |
| isInteger (Lecture seule) | True if the raster dataset has an integer type. | Boolean |
| isTemporary (Lecture seule) | True if the raster dataset is temporary, or False if it is permanent. | Boolean |
| maximum (Lecture seule) | The maximum value in the referenced raster dataset. | Double |
| mean (Lecture seule) | The mean value in the referenced raster dataset. | Double |
| meanCellHeight (Lecture seule) | The cell size in the y direction. | Double |
| meanCellWidth (Lecture seule) | The cell size in the x direction. | Double |
| minimum (Lecture seule) | The minimum value in the referenced raster dataset. | Double |
| name (Lecture seule) | The name of the referenced raster dataset. | String |
| noDataValue (Lecture seule) | The NoData value of the referenced raster dataset. | Double |
| path (Lecture seule) | The full path of the referenced raster dataset. | String |
| pixelType (Lecture seule) | The pixel type of the referenced raster dataset. The types are the following:
| String |
| spatialReference (Lecture seule) | The spatial reference of the referenced raster dataset. | SpatialReference |
| standardDeviation (Lecture seule) | The standard deviation of the values in the referenced raster dataset. | Double |
| uncompressedSize (Lecture seule) | The size of the referenced raster dataset on disk. | Double |
| width (Lecture seule) | The number of columns. | Integer |
Vue d’ensemble des méthodes
| Méthode | Explication |
| save ({name}) | Permanently saves the dataset referenced by the raster object. |
Méthodes
save ({name})| Paramètre | Explication | Type de données |
name | The name to assign to the raster dataset on disk. | String |
Exemple de code
Raster example 1
Creates a Raster object from a raster dataset and gets properties for analysis.
import arcpy
my_raster = arcpy.Raster('elevation')
my_min = my_raster.minimum
my_max = my_raster.maximum
my_area = (my_raster.width * my_raster.height) * my_raster.meanCellWidth
Raster example 2
Creates a Raster object, gets properties, creates a random error raster (+/- 3 feet), adds it to an elevation raster, and converts its units from feet to meters.
import arcpy
from arcpy.sa import *
elev_raster = Raster('c:/data/elevation')
my_extent = elev_raster.extent
my_cellsize = (elev_raster.meanCellHeight + elev_raster.meanCellWidth) / 2
res01 = arcpy.CreateRandomRaster_management("", "error3", "UNIFORM 0.0 3.0",
my_extent, my_cellsize)
elev_meters = (elev_raster + Raster(res01)) * 0.3048
elev_meters.save("c:/output/fgdb.gdb/elevM_err")