| Label | Explanation | Data Type |
Input raster | The input elevation surface raster. | Raster Layer |
Input points feature or table | The input point feature class or table specifying the locations to analyze solar radiation. | Feature Layer; Table View |
Output global radiation features | The output feature class representing the global radiation or amount of incoming solar insolation (direct + diffuse) calculated for each location. The output has units of watt hours per square meter (WH/m2). | Feature Class |
Height offset (Optional) | The height (in meters) above the DEM surface for which calculations will be performed. The height offset will be applied to all input locations. | Double |
Latitude (Optional) | The latitude for the site area. The units are decimal degrees with positive values for the northern hemisphere and negative values for the southern hemisphere. For input surface rasters containing a spatial reference, the mean latitude is automatically calculated; otherwise, the latitude default is 45 degrees. | Double |
Sky size / Resolution (Optional) | The resolution or sky size for the viewshed, sky map, and sun map rasters. The units are cells. The default is a raster of 200 by 200 cells. | Long |
Time configuration (Optional) | Specifies the time period that will be used for the calculations.
| Time configuration |
Day interval (Optional) | The time interval through the year (units: days) that will be used to calculate sky sectors for the sun map. The default value is 14 (biweekly). | Long |
Hour interval (Optional) | The time interval through the day (units: hours) that will be used to calculate sky sectors for the sun map. The default value is 0.5. | Double |
Create outputs for each interval (Optional) | Specifies whether a single total insolation value will be calculated for all locations or multiple values will be calculated for the specified hour and day interval.
| Boolean |
Z factor (Optional) | The number of ground x,y units in one surface z-unit. The z-factor adjusts the units of measure for the z-units when they are different from the x,y units of the input surface. The z-values of the input surface are multiplied by the z-factor when calculating the final output surface. If the x,y units and z-units are in the same units of measure, the z-factor is 1. This is the default. If the x,y units and z-units are in different units of measure, the z-factor must be set to the appropriate factor or the results will be incorrect. For example, if the z-units are feet and the x,y units are meters, use a z-factor of 0.3048 to convert the z-units from feet to meters (1 foot = 0.3048 meter). | Double |
Slope and aspect input type (Optional) | Specifies how slope and aspect information will be derived for analysis.
| String |
Calculation directions (Optional) | The number of azimuth directions that will be used when calculating the viewshed. Valid values must be multiples of 8 (8, 16, 24, 32, and so on). The default value is 32 directions, which is adequate for complex topography. | Long |
Zenith divisions (Optional) | The number of zenith divisions that will be used to create sky sectors in the sky map. The default is eight divisions (relative to zenith). Values must be greater than zero and less than half the sky size value. | Long |
Azimuth divisions (Optional) | The number of azimuth divisions that will be used to create sky sectors in the sky map. The default is eight divisions (relative to north). Valid values must be multiples of 8. Values must be greater than zero and less than 160. | Long |
Diffuse model type (Optional) | Specifies the type of diffuse radiation model that will be used.
| String |
Diffuse proportion (Optional) | The proportion of global normal radiation flux that is diffuse. Values range from 0 to 1. Set this value according to atmospheric conditions. The default value is 0.3 for generally clear sky conditions. | Double |
Transmittivity (Optional) | The fraction of radiation that passes through the atmosphere (averaged overall wavelengths). Values range from 0 (no transmission) to 1 (all transmission). The default is 0.5 for a generally clear sky. | Double |
Output direct radiation features (Optional) | The output feature class representing the direct incoming solar radiation for each location. The output has units of watt hours per square meter (WH/m2). | Feature Class |
Output diffuse radiation features (Optional) | The output feature class representing the incoming solar radiation for each location that is diffuse. The output has units of watt hours per square meter (WH/m2). | Feature Class |
Output direct duration features (Optional) | The output feature class representing the duration of direct incoming solar radiation. The output has units of hours. | Feature Class |
Available with Spatial Analyst license.
Summary
Derives incoming solar radiation for specific locations in a point feature class or location table.
Usage
The input locations can be a point feature class or a table of point coordinates. The table can be a geodatabase table, a .dbf file, an INFO table, or a text table file. The values can be of type long integer, float, or double.
When inputting locations by table, a list of locations must be specified with an x,y coordinate. Using an ASCII coordinate file, each line should contain an x,y pair separated by a comma, space, or tab. The following is a space-delimited example:
X Y 325541.218750 4314768.5 325169.250000 4313907.0 325874.031250 4313134.0 325825.093750 4314181.5
Alternatively, you can specify slope (degrees) and aspect in the location table. Along with the x,y coordinate, the file should contain the slope and aspect value for each location, in either order. The following is a comma-delimited example:
x, y, slope, aspect 325541.218750, 4314768.5, 15.84516716, 310.2363586 325169.250000, 4313907.0, 39.39801788, 2.03503442 325874.031250, 4313134.0, 16.10847282, 223.8308563 325825.093750, 4314181.5, 8.89850712, 205.2011261
For multiday time configurations, the maximum range of days is a total of one year (365 days, or 366 days for leap years). If the start day is greater than the end day, the time calculations will proceed into the following year.
For example, [start day, end day] = [365, 31] represents December 31 to January 31 of the following year. For the example of [1, 2], the time is inclusive for the first day from 0:00 hours (January 1) to 0:00 (January 2). The start day and end day cannot be equal.
The year value for time configuration is used to determine a leap year. It does not have any other influence on the solar radiation analysis, as the calculations are a function of the time period determined by Julian days.
For within-day time configurations, the maximum range of time is one day (24 hours). Calculations will not be performed across days (for instance, from 12:00 p.m. to 12:00 p.m. the next day). The start time must be less than the end time.
The use of a z-factor is essential for correcting calculations when the surface z-units are expressed in units different from the ground x,y units. For accurate results, the z-units should be the same as the x,y ground units. If the units are not the same, use a z-factor to convert z-units to x,y units. For example, if the x,y units are meters and the z-units are feet, you can specify a z-factor of 0.3048 to convert feet to meters.
It is recommended that you have your data in a projected coordinate system with units of meters. If you run the analysis with a spherical coordinate system, you will need to specify an appropriate z-factor for that latitude. The following is a list of some appropriate z-factors to use if the x,y units are decimal degrees and the z-units are meters:
Latitude Z-factor 0 0.00000898 10 0.00000912 20 0.00000956 30 0.00001036 40 0.00001171 50 0.00001395 60 0.00001792 70 0.00002619 80 0.00005156The height offset must be specified in meters.
The latitude for the site area (units: decimal degree, positive for the northern hemisphere and negative for the southern hemisphere) is used in calculations such as solar declination and solar position. Because the solar analysis is designed for landscape scales and local scales, it is acceptable to use one latitude value for the whole DEM. For broader geographic regions, you must divide the study area into zones with different latitudes.
For input surface rasters containing a spatial reference, the mean latitude is automatically calculated; otherwise, the latitude default is 45 degrees. When using an input layer, the spatial reference of the data frame is used.
Sky size is the resolution of the viewshed, sky map, and sun map rasters that are used in the radiation calculations (units: cells per side). These are upward-looking, hemispherical raster representations of the sky and do not have a geographic coordinate system. These rasters are square (equal number of rows and columns).
The following are recommended sky size values when a time configuration of a whole year or multiple days is used:
- For a 1 day interval, use a sky size of 1000 and above.
- For a 0.25 day interval, use a sky size of 2000 and above.
- For a 0.1 hour interval, use a sky size of 4000 and above.
Increasing the sky size increases calculation accuracy but also increases calculation time considerably.
When the day interval setting is small (for example, < 14 days), use a larger sky size. During analysis, the sun map (determined by the sky size) is used to represent sun positions (tracks) for particular time periods to calculate direct radiation. With smaller day intervals, if the sky size resolution is not large enough, sun tracks may overlap, resulting in zero or lower radiation values for that track. Increasing the resolution provides a more accurate result.
The maximum sky size value is 10,000. A value of 200 is the default and is sufficient for whole DEMs with large day intervals (for example, > 14 days). A sky size value of 512 is sufficient for calculations at point locations where calculation time is less of an issue. At smaller day intervals (for example, < 14 days), it is recommended that you use higher values. For example, to calculate insolation for a location at the equator with day interval = 1, use a sky size of 2,800 or above.
Day intervals greater than 3 are recommended, as sun tracks within three days typically overlap, depending on sky size and time of year. For calculations of the whole year with monthly interval, day interval is disabled and the program uses calendar month intervals. The default value is 14.
Because the viewshed calculation can be highly intensive, horizon angles are only traced for the number of calculation directions specified. Valid values must be multiples of 8 (8, 16, 24, 32, and so on). Typically, a value of 8 or 16 is adequate for areas with gentle topography, whereas a value of 32 is adequate for complex topography. The default value is 32.
The number of calculation directions needed is related to the resolution of the input DEM. Natural terrain at 30-meters resolution is usually quite smooth, so fewer directions are sufficient for most situations (16 or 32). With finer DEMs, and particularly with human-made structures incorporated in the DEMs, the number of directions needs to increase. Increasing the number of directions increases accuracy but also increase calculation time.
The Create outputs for each interval check box provides the flexibility to calculate insolation integrated over a specified time period or insolation for each interval in a time series. For example, for the within-day time period with an hour interval of one, checking this box will create hourly insolation values; otherwise, insolation integrated for the entire day is calculated.
The Create outputs for each interval parameter affects the number of attributes for output features. When checked for point radiation analysis, the output feature class includes additional attributes (t0, t1, t2, and so on), which indicate radiation or duration values for each time interval (hour interval when time configuration is less than one day, or day interval when multiple days). If, for example, start time = 0, then t0 will be sun rise and t1 will be at the next time increment after sun rise.
The amount of solar radiation received by the surface is only a portion of what would be received outside the atmosphere. Transmittivity is a property of the atmosphere that is expressed as the ratio of the energy (averaged overall wavelengths) reaching the earth's surface to that which is received at the upper limit of the atmosphere (extraterrestrial). Values range from 0 (no transmission) to 1 (complete transmission). Typically observed values are 0.6 or 0.7 for very clear sky conditions and 0.5 for a generally clear sky.
The value for the energy received at the earth's surface is at the shortest path through the atmosphere (that is, the sun is at the zenith, or directly overhead) and for sea level. For areas beyond Tropic of Capricorn and Tropic of Cancer, the sun can never be at the exact zenith, even at noon; however, this value still refers to the moment when the sun is at the zenith. Because the algorithm corrects for elevation effects, transmittivity should always be given for sea level.
Transmittivity has an inverse relation with the diffuse proportion parameter.
See Analysis environments and Spatial Analyst for additional details on the geoprocessing environments that apply to this tool.
Parameters
PointsSolarRadiation(in_surface_raster, in_points_feature_or_table, out_global_radiation_features, {height_offset}, {latitude}, {sky_size}, {time_configuration}, {day_interval}, {hour_interval}, {each_interval}, {z_factor}, {slope_aspect_input_type}, {calculation_directions}, {zenith_divisions}, {azimuth_divisions}, {diffuse_model_type}, {diffuse_proportion}, {transmittivity}, {out_direct_radiation_features}, {out_diffuse_radiation_features}, {out_direct_duration_features})| Name | Explanation | Data Type |
in_surface_raster | The input elevation surface raster. | Raster Layer |
in_points_feature_or_table | The input point feature class or table specifying the locations to analyze solar radiation. | Feature Layer; Table View |
out_global_radiation_features | The output feature class representing the global radiation or amount of incoming solar insolation (direct + diffuse) calculated for each location. The output has units of watt hours per square meter (WH/m2). | Feature Class |
height_offset (Optional) | The height (in meters) above the DEM surface for which calculations will be performed. The height offset will be applied to all input locations. | Double |
latitude (Optional) | The latitude for the site area. The units are decimal degrees with positive values for the northern hemisphere and negative values for the southern hemisphere. For input surface rasters containing a spatial reference, the mean latitude is automatically calculated; otherwise, the latitude default is 45 degrees. | Double |
sky_size (Optional) | The resolution or sky size for the viewshed, sky map, and sun map rasters. The units are cells. The default is a raster of 200 by 200 cells. | Long |
time_configuration (Optional) | Specifies the time configuration (period) that will be used for calculating solar radiation. The Time class objects are used to specify the time configuration. The different types of time configurations available are TimeWithinDay, TimeMultipleDays, TimeSpecialDays, and TimeWholeYear. The following are the forms:
The default time configuration is TimeMultipleDays with the startDay value of 5 and the endDay value of 160 for the current Julian year. | Time configuration |
day_interval (Optional) | The time interval through the year (units: days) that will be used to calculate sky sectors for the sun map. The default value is 14 (biweekly). | Long |
hour_interval (Optional) | The time interval through the day (units: hours) that will be used to calculate sky sectors for the sun map. The default value is 0.5. | Double |
each_interval (Optional) | Specifies whether a single total insolation value will be calculated for all locations or multiple values will be calculated for the specified hour and day interval.
| Boolean |
z_factor (Optional) | The number of ground x,y units in one surface z-unit. The z-factor adjusts the units of measure for the z-units when they are different from the x,y units of the input surface. The z-values of the input surface are multiplied by the z-factor when calculating the final output surface. If the x,y units and z-units are in the same units of measure, the z-factor is 1. This is the default. If the x,y units and z-units are in different units of measure, the z-factor must be set to the appropriate factor or the results will be incorrect. For example, if the z-units are feet and the x,y units are meters, use a z-factor of 0.3048 to convert the z-units from feet to meters (1 foot = 0.3048 meter). | Double |
slope_aspect_input_type (Optional) | Specifies how slope and aspect information will be derived for analysis.
| String |
calculation_directions (Optional) | The number of azimuth directions that will be used when calculating the viewshed. Valid values must be multiples of 8 (8, 16, 24, 32, and so on). The default value is 32 directions, which is adequate for complex topography. | Long |
zenith_divisions (Optional) | The number of zenith divisions that will be used to create sky sectors in the sky map. The default is eight divisions (relative to zenith). Values must be greater than zero and less than half the sky size value. | Long |
azimuth_divisions (Optional) | The number of azimuth divisions that will be used to create sky sectors in the sky map. The default is eight divisions (relative to north). Valid values must be multiples of 8. Values must be greater than zero and less than 160. | Long |
diffuse_model_type (Optional) | Specifies the type of diffuse radiation model that will be used.
| String |
diffuse_proportion (Optional) | The proportion of global normal radiation flux that is diffuse. Values range from 0 to 1. Set this value according to atmospheric conditions. The default value is 0.3 for generally clear sky conditions. | Double |
transmittivity (Optional) | The fraction of radiation that passes through the atmosphere (averaged overall wavelengths). Values range from 0 (no transmission) to 1 (all transmission). The default is 0.5 for a generally clear sky. | Double |
out_direct_radiation_features (Optional) | The output feature class representing the direct incoming solar radiation for each location. The output has units of watt hours per square meter (WH/m2). | Feature Class |
out_diffuse_radiation_features (Optional) | The output feature class representing the incoming solar radiation for each location that is diffuse. The output has units of watt hours per square meter (WH/m2). | Feature Class |
out_direct_duration_features (Optional) | The output feature class representing the duration of direct incoming solar radiation. The output has units of hours. | Feature Class |
Code sample
The following Python window script demonstrates how to use this tool.
import arcpy
from arcpy import env
from arcpy.sa import *
env.workspace = "C:/sapyexamples/data"
PointsSolarRadiation("elevation", "observers.shp",
"c:/sapyexamples/output/outglobalrad1.shp", "", 35, 200,
TimeMultipleDays(2009, 91, 212), 14, 0.5,"NOINTERVAL",
1, "FROM_DEM", 32, 8, 8,"STANDARD_OVERCAST_SKY", 0.3, 0.5,
"c:/sapyexamples/output/outdirectrad1.shp",
"c:/sapyexamples/output/outdiffuserad1.shp",
"c:/sapyexamples/output/outduration1.shp")Calculate the amount of incoming solar radiation for specific point locations.
# PointsSolarRadiation_Example02.py
# Description: For all point locations, calculates total global, direct,
# diffuse and direct duration solar radiation for a whole year.
# Requirements: Spatial Analyst Extension
# Import system modules
import arcpy
from arcpy import env
from arcpy.sa import *
# Set environment settings
env.workspace = "C:/sapyexamples/data"
# Set local variables
inRaster = "elevation"
inPntFC = "observers.shp"
outFeatures = "c:/sapyexamples/output/outglobal1.shp"
latitude = 35.75
skySize = 200
timeConfig = TimeMultipleDays(2009, 91, 212)
dayInterval = 14
hourInterval = 0.5
zFactor = 0.3048
calcDirections = 32
zenithDivisions = 8
azimuthDivisions = 8
diffuseProp = 0.3
transmittivity = 0.5
outDirectRad = "C:/sapyexamples/output/outdirectrad1.shp"
outDiffuseRad = "C:/sapyexamples/output/outdiffuserad1.shp"
outDirectDur = "C:/sapyexamples/output/outduration1.shp"
# Execute PointsSolarRadiation...
PointsSolarRadiation(inRaster, inPntFC, outFeatures, "", latitude, skySize,
timeConfig, dayInterval, hourInterval, "INTERVAL",
zFactor, "FROM_DEM", calcDirections, zenithDivisions,
azimuthDivisions,"STANDARD_OVERCAST_SKY", diffuseProp,
transmittivity, outDirectRad, outDiffuseRad, outDirectDur)Environments
Licensing information
- Basic: Requires Spatial Analyst
- Standard: Requires Spatial Analyst
- Advanced: Requires Spatial Analyst