Performance Performance is fundamentally limited by: –Size of data –Where the data is stored –Type of processing –Processing software –Hardware available

Real Performance Limitations Rasters: Size of the data and number of files Points: Number of rows, number of size of attributes Network access, especially services ArcGIS tools Mistakes in processing Hardware

Size of Digital Values Number of binary digits EquationNumber of possible valuesMinimum Value Maximum Value 1 (bit)2^ ^ ^ (nibble)2^ ^ ^ ^ (byte)2^ ^ ^ ^ ^ (word)2^ ^ ^ ^ ^ ^ ^

Range of Computer Numbers BitsNameNumber of values / Precision MinimumMaximumUses 8-bit integerByte RS 16-bit unsigned integer Unsigned short DEMs 16-bit signed integerSigned short DEMs 32-bit integerLong integer ~4 billion~ -2 billion~2 billionCounts, Categorical 32-bit floatFloat7-8- ~ ~ Continuous 64-bit floatDouble ~ ~ Continuous

Performance By Type TypeCalculationsQueriesBytes 16-bit unsigned integerFast 2 16-bit signed integerFast 2 32-bit signedFast 4 32-bit floatFastModerate4 64-bit floatFastModerate8 DateSlow 7 and up StringsSlow 1 and up

4 Resolutions of Remote Sensing Spatial: –X and Y resolution Spectral: –Number of bands Temporal: –Number of samples per time unit Radiometric: –Number of bits or bytes per sample

Raster Structure Sample Pixel: All the samples that are coincident X Dimension Y Dimension Band 0 Band 1 Band 2

Raster Resolutions Spatial Resolution: –Width and height of each sample/pixel Spectral Resolution: –Number of widths of the bands Radiometric Resolution: –Number of bits per band Temporal Resolution: –Number of rasters per time interval

Raster Resolutions Spatial: –10 cm to 1 km Spectral (Number of Bands): –3 for photos, 7 for Landsat, for 256 MODIS Temporal: –Daily for MODIS, 15 days for Landsat, every few years for SRTM Radiometric (Sample Depth): –8 bits=0 to 255 (256 shades)

Raster Size Size in Bytes = Width of the area * Resolution * Height of the area * Resolution * Bytes per band * Number of bands * Number of Temporal Slices

Landsat TM Scene Sensor type: opto-mechanical Spatial Resolution: 30 m (120 m - thermal) Spectral Range: µm Number of Bands: 7 Temporal Resolution: 16 days Image Size: 185 km X 172 km Swath: 185 km Programmable: yes

Improving Performance It used to be storing the data was a major problem Today, the problem is getting the computer processor “close” to the data

Improving Performance Resample rasters to the size desired Clip rasters to the area of interest Only use the bands required Store or “cache” rasters to the computer doing the processing Include performance evaluation as part of the modeling design