arcgis.raster.orthomapping module¶

The orthomapping python API allows automating orthomapping tasks in the server environment.

For more information about orthomapping workflows in ArcGIS, please visit the help documentation at Block adjustment for mosaic datasets

is_supported¶

arcgis.raster.orthomapping.is_supported(gis=None)¶: Returns True if the GIS supports orthomapping. If a gis isn’t specified, checks if active_gis() supports raster analytics

compute_sensor_model¶

arcgis.raster.orthomapping.compute_sensor_model(image_collection, mode='Quick', location_accuracy='High', context=None, *, gis=None, future=False, **kwargs)¶

compute_sensor_model computes the bundle block adjustment for the image collection and applies the frame xform to the images. It will also generate the control point table, solution table, solution points table and flight path table. These tables will not be published as Portal items.

Parameter	Description
image_collection	Required, the input image collection on which to compute the sensor model. The image_collection can be a portal Item or an image service URL or a URI The image_collection must exist.
mode	Optional string. the mode to be used for bundle block adjustment Only the following modes are supported: ‘Quick’ : Computes tie points and adjustment at 8x of the source imagery resolution ‘Full’ : adjust the images in Quick mode then at 1x of the source imagery resolution ‘Refine’ : adjust the image at 1x of the source imagery resolution By default, ‘Quick’ mode is applied to compute the sensor model.
location_acuracy	Optional string. this option allows users to specify the GPS location accuracy level of the source image. It determines how far the underline tool will search for neighboring matching images, then calculate tie points and compute adjustments. Possible values for location_accuracy are: ‘High’ : GPS accuracy is 0 to 10 meters, and the tool uses a maximum of 4 by 3 images ‘Medium’ : GPS accuracy of 10 to 20 meters, and the tool uses a maximum of 4 by 6 images ‘Low’ : GPS accuracy of 20 to 50 meters, and the tool uses a maximum of 4 by 12 images ‘VeryLow’ : GPS accuracy is more than 50 meters, and the tool uses a maximum of 4 by 20 images The default location_accuracy is ‘High’
context	Optional dictionary. The context parameter is used to configure additional client settings for block adjustment. The supported configurable parameters are for compute mosaic dataset candidates after the adjustment. Example: { “computeCandidate”: False, “maxoverlap”: 0.6, “maxloss”: 0.05, }
gis	Optional `GIS` . The GIS on which this tool runs. If not specified, the active GIS is used.

Returns: The imagery layer url

alter_processing_states¶

arcgis.raster.orthomapping.alter_processing_states(image_collection, new_states, *, gis=None, future=False, **kwargs)¶

Alter the processing states of the image collection. The states are stored as key property “Orthomapping”. The content of the state is a dictionary including several properties which can be set based on the process done on the image collection.

Parameter	Description
image_collection	Required, This is the image collection that will be adjusted. The image_collection can be a portal Item or an image service URL or URI The image_collection must exist.
new_states	Required dictionary. The state to set on the image_collection This a dictionary of states that should be set on the image collection The new states that can be set on the image collection are: blockadjustment, dem, gcp, seamlines, colorcorrection, adjust_index, imagetype Example: {“blockadjustment”: “raw”, “dem”: “Dense_Natual_Neighbor”, “seamlines”:”VORONOI”, “colorcorrection”:”SingleColor”, “imagetype”: “UAV/UAS”, “adjust_index”: 0}
gis	Optional `GIS` . The GIS on which this tool runs. If not specified, the active GIS is used.

Returns: The result will be the newly set states dictionary

get_processing_states¶

arcgis.raster.orthomapping.get_processing_states(image_collection, *, gis=None, future=False, **kwargs)¶

Retrieve the processing states of the image collection

Parameter

Description

image_collection

Required, This is the image collection that will be adjusted.

The image_collection can be a portal Item or an image service URL or URI

The image_collection must exist.

gis

Optional GIS . The GIS on which this tool runs. If not specified, the active GIS is used.

Returns: The result will be the newly set states dictionary

match_control_points¶

arcgis.raster.orthomapping.match_control_points(image_collection, control_points, similarity='High', context=None, *, gis=None, future=False, **kwargs)¶

The match_control_points is a function that takes a collection of ground control points as input (control points to be specified as a list of dictionary objects), and each of the ground control points needs at least one matching tie point in the control point sets. The function will compute the remaining matching tie points for all control point sets.

Parameter	Description
image_collection	Required, the input image collection that will be adjusted. The image_collection can be a portal Item or an image service URL or a URI The image_collection must exist.
control_points	Required, a list of control point sets objects. The schema of control points follows the schema of the mosaic dataset control point table. The control point object should contain the point geometry, pointID, type, status and the imagePoints. (the imagePoints attribute inside the control points object lists the imageIDs) – pointID (int) - The ID of the point within the control point table. – type (int) - The type of the control point as determined by its numeric value 1: Tie Point 2: Ground Control Point. 3: Check Point – status (int) - The status of the point. A value of 0 indicates that the point will not be used in computation. A non-zero value indicates otherwise. – imageID (int) - Image identification using the ObjectID from the mosaic dataset footprint table. Example: [{ “status”: 1, “type”: 2, “x”: -117.0926538, “y”: 34.00704253, “z”: 634.2175, “spatialReference”: { “wkid”: 4326 }, // default WGS84 “imagePointSpatialReference”: {}, // default ICS “pointId”: 1, “xyAccuracy”: “0.008602325”, “zAccuracy”: “0.015”, “imagePoints”: [{ “imageID”: 1, “x”: 2986.5435987557084, “y”: -2042.5193648409431, “u”: 3057.4580682832734, “v”: -1909.1506872159698 }, { “imageID”: 2, “x”: 1838.2814361401108, “y”: -2594.5280063817972, “u”: 3059.4079724863363, “v”: -2961.292545463305 }, { “imageID”: 12, “x”: 5332.855578204663, “y”: -2533.2805429751907, “u”: 614.2338676573158, “v”: -165.10836768947297 }, { “imageID”: 13, “x”: 4932.0895715254455, “y”: -1833.8401744114287, “u”: 616.9396928182223, “v”: -1243.1445126959693 }] }, … … ]
similarity	Optional string. Choose the tolerance level for your control point matching. Low- The similarity tolerance for finding control points will be low. This option will produce the most control points, but some may have a higher level of error. Medium - The similarity tolerance for finding control points will be medium. High - The similarity tolerance for finding control points will be high. This option will produce the least number of control points, but each matching pair will have a lower level of error. This is the default.
context	Optional dictionary.Additional settings such as the input control points spatial reference can be specified here. For Example: {“groundControlPointsSpatialReference”: {“wkid”: 3459}, “imagePointSpatialReference”: {“wkid”: 3459}} Note: The ground control points spatial reference and image point spatial reference spatial reference set in the context parameter is to decide the returned point set’s ground control points spatial reference and image point spatial reference. If these two parameters are not set here, the tool will use the spatial reference defined in the input point set. And if no spatial reference is defined in the point set, then the default ground control points coordinates are in lon/lat and image points coordinates are in image coordinate system.
gis	Optional `GIS` . The GIS on which this tool runs. If not specified, the active GIS is used.

Returns: A list of dictionary objects

color_correction¶

arcgis.raster.orthomapping.color_correction(image_collection, color_correction_method, dodging_surface_type, target_image=None, context=None, *, gis=None, future=False, **kwargs)¶

Color balance the image collection. Refer to the Color Balance Mosaic Dataset GP tool for documentation on color balancing mosaic datasets.

Parameter	Description
image_collection	Required. This is the image collection that will be adjusted. The image_collection can be a portal Item or an image service URL or a URI The image_collection must exist.
color_correction_method	Required string. This is the method that will be used for color correction computation. The available options are: Dodging-Change each pixel’s value toward a target color. With this technique, you must also choose the type of target color surface, which affects the target color. Dodging tends to give the best result in most cases. Histogram-Change each pixel’s value according to its relationship with a target histogram. The target histogram can be derived from all of the rasters, or you can specify a raster. This technique works well when all of the rasters have a similar histogram. Standard_Deviation-Change each of the pixel’s values according to its relationship with the histogram of the target raster, within one standard deviation. The standard deviation can be calculated from all of the rasters in the mosaic dataset, or you can specify a target raster. This technique works best when all of the rasters have normal distributions.
dodging_surface_type	Required string.When using the Dodging balance method, each pixel needs a target color, which is determined by the surface type. Single_Color-Use when there are only a small number of raster datasets and a few different types of ground objects. If there are too many raster datasets or too many types of ground surfaces, the output color may become blurred. All the pixels are altered toward a single color point-the average of all pixels. Color_Grid- Use when you have a large number of raster datasets, or areas with a large number of diverse ground objects. Pixels are altered toward multiple target colors, which are distributed across the mosaic dataset. First_Order- This technique tends to create a smoother color change and uses less storage in the auxiliary table, but it may take longer to process compared to the color grid surface. All pixels are altered toward many points obtained from the two-dimensional polynomial slanted plane. Second_Order-This technique tends to create a smoother color change and uses less storage in the auxiliary table, but it may take longer to process compared to the color grid surface. All input pixels are altered toward a set of multiple points obtained from the two-dimensional polynomial parabolic surface. Third_Order-This technique tends to create a smoother color change and uses less storage in the auxiliary table, but it may take longer to process compared to the color grid surface. All input pixels are altered toward multiple points obtained from the cubic surface.
target_image	Optional. The image service you want to use to color balance the images in the image collection. It can be a portal Item or an image service URL or a URI
context	Optional dictionary. It contains additional settings that allows users to customize the statistics computation settings. Example: {“skipRows”: 10, “skipCols”: 10, “reCalculateStats”: “OVERWRITE”}
gis	Optional `GIS` . the GIS on which this tool runs. If not specified, the active GIS is used.

Returns: The imagery layer url

compute_control_points¶

arcgis.raster.orthomapping.compute_control_points(image_collection, reference_image=None, image_location_accuracy='High', context=None, *, gis=None, future=False, **kwargs)¶

This service tool is used for computing matching control points between images within an image collection and/or matching control points between the image collection images and the reference image. Compute Control Points

Parameter	Description
image_collection	Required. This is the image collection that will be adjusted. The image_collection can be a portal Item or an image service URL or a URI The image_collection must exist.
reference_image	This is the reference image service that can be used to generate ground control points set with the image service. It can be a portal Item or an image service URL or a URI
image_location_accuracy	Optional string. This option allows you to specify the GPS location accuracy level of the source image. It determines how far the tool will search for neighboring matching images for calculating tie points and block adjustments. The following are the available options: Low, Medium, High Low- GPS accuracy of 20 to 50 meters, and the tool uses a maximum of 4 by 12 images. Medium- GPS accuracy of 10 to 20 meters, and the tool uses a maximum of 4 by 6 images. High- GPS accuracy of 0 to 10 meters, and the tool uses a maximum of 4 by 3 images. If the image collection is created from satellite data, it will be automatically switched to use RPC adjustment mode. In this case, the mode need not be explicitly set by the user. Default is High
context	Optional dictionary. Context contains additional environment settings that affect output control points generation. Possible keys and their possible values are: pointSimilarity- Sets LOW, MEDIUM, or HIGH tolerance for computing control points with varying levels of potential error. LOW tolerance will produce the most control point, but may have a higher level of error. HIGH tolerance will produce the least number of control point, but each matching pair will have a lower level of error. MEDIUM tolerance will set the similarity tolerance to medium. pointDensity- Sets the number of tie points (LOW, MEDIUM, or HIGH), to be created. LOW point density will create the fewest number of tie points. MEDIUM point density will create a moderate number of tie points. HIGH point density will create the highest number of tie points. pointDistribution- Randomly generates points that are better for overlapping areas with irregular shapes. RANDOM- will generate points that are better for overlapping areas with irregular shapes. REGULAR- will generate points based on a fixed pattern and uses the point density to determine how frequently to create points. Example: { “pointSimilarity”:”MEDIUM”, “pointDensity”: “MEDIUM”, “pointDistribution”: “RANDOM” }
gis	Optional `GIS` . the GIS on which this tool runs. If not specified, the active GIS is used.

Returns: The imagery layer url

compute_seamlines¶

arcgis.raster.orthomapping.compute_seamlines(image_collection, seamlines_method, context=None, *, gis=None, future=False, **kwargs)¶

Compute seamlines on the image collection. This service tool is used to compute seamlines for the image collection, usually after the image collection has been block adjusted. Seamlines are helpful for generating the seamless mosaicked display of overlapped images in image collection. The seamlines are computed only for candidates that will eventually be used for generating the result ortho-mosaicked image.

Build Seamlines

Parameter	Description
image_collection	Required, the input image collection that will be adjusted. The image_collection can be a portal Item or an image service URL or a URI The image_collection must exist.
seamlines_method	Required string. These are supported methods for generated seamlines for the image collection. VORONOI-Generate seamlines using the area Voronoi diagram. DISPARITY-Generate seamlines based on the disparity images of stereo pairs. GEOMETRY - Generate seamlines for overlapping areas based on the intersection of footprints. Areas with no overlapping imagery will merge the footprints. RADIOMETRY - Generate seamlines based on the spectral patterns of features within the imagery. EDGE_DETECTION - Generate seamlines over intersecting areas based on the edges of features in the area. This method can avoid seamlines cutting through buildings.
context	Optional dictionary. Context contains additional settings that allows users to customize the seamlines generation. Example: {“minRegionSize”: 100, “pixelSize”: “”, “blendType”: “Both”, “blendWidth”: null, “blendUnit”: “Pixels”, “requestSizeType”: “Pixels”, “requestSize”: 1000, “minThinnessRatio”: 0.05, “maxSilverSize”: 20 } Allowed keys are: “minRegionSize”, “pixelSize”, “blendType”, “blendWidth”, “blendUnit”, “requestSizeType”, “requestSize”, “minThinnessRatio”, “maxSilverSize”
gis	Optional `GIS` . The GIS on which this tool runs. If not specified, the active GIS is used.

Returns: The Imagery layer url

edit_control_points¶

arcgis.raster.orthomapping.edit_control_points(image_collection, control_points, *, gis=None, future=False, **kwargs)¶

This service can be used to append additional ground control point sets to the image collection’s control points. It is recommended that a ground control point (GCP) set should contain one ground control point and multiple tie points. The service tool can also be used to edit tie point sets. The input control points dictionary will always replace the points in the tie points table if the point IDs already exist.

Parameter	Description
image_collection	Required. The image_collection can be a portal Item or an image service URL or a URI The image_collection must exist.
control_points	Required, a list of control point sets objects. The schema of control points follows the schema of the mosaic dataset control point table. The control point object should contain the point geometry, pointID, type, status and the imagePoints. (the imagePoints attribute inside the control points object lists the imageIDs) – pointID (int) - The ID of the point within the control point table. – type (int) - The type of the control point as determined by its numeric value 1: Tie Point 2: Ground Control Point. 3: Check Point – status (int) - The status of the point. A value of 0 indicates that the point will not be used in computation. A non-zero value indicates otherwise. – imageID (int) - Image identification using the ObjectID from the mosaic dataset footprint table. Example: [{ “status”: 1, “type”: 2, “x”: -117.0926538, “y”: 34.00704253, “z”: 634.2175, “spatialReference”: { “wkid”: 4326 }, // default WGS84 “imagePointSpatialReference”: {}, // default ICS “pointId”: 1, “xyAccuracy”: “0.008602325”, “zAccuracy”: “0.015”, “imagePoints”: [{ “imageID”: 1, “x”: 2986.5435987557084, “y”: -2042.5193648409431, “u”: 3057.4580682832734, “v”: -1909.1506872159698 }, { “imageID”: 2, “x”: 1838.2814361401108, “y”: -2594.5280063817972, “u”: 3059.4079724863363, “v”: -2961.292545463305 }, { “imageID”: 12, “x”: 5332.855578204663, “y”: -2533.2805429751907, “u”: 614.2338676573158, “v”: -165.10836768947297 }, { “imageID”: 13, “x”: 4932.0895715254455, “y”: -1833.8401744114287, “u”: 616.9396928182223, “v”: -1243.1445126959693 }] }, … … ]
gis	Optional `GIS` . The GIS on which this tool runs. If not specified, the active GIS is used.

Returns: The Imagery layer url

generate_dem¶

arcgis.raster.orthomapping.generate_dem(image_collection, out_dem, cell_size, surface_type, matching_method=None, context=None, *, gis=None, future=False, **kwargs)¶

Generate a DEM from the image collection. Refer to Interpolate From Point Cloud GP tool for more documentation

Parameter	Description
image_collection	Required. The input image collection that will be used to generate the DEM from. The image_collection can be a portal Item or an image service URL or a URI The image_collection must exist.
out_dem	This is the output digital elevation model. It can be a url, uri, portal item, or string representing the name of output dem (either existing or to be created.) Like Raster Analysis services, the service can be an existing multi-tenant service URL.
cell_size	Required, The cell size of the output raster dataset. This is a single numeric input. Rectangular cell size such as {“x”: 10, “y”: 10} is not supported. The cell size unit will be the unit used by the image collection’s spatial reference.
surface_type	Required string. Create a digital terrain model or a digital surface model. Refer to “surface_type” parameter of the GP tool. The available choices are: DTM - Digital Terrain Model, the elevation is only the elevation of the bare earth, not including structures above the surface. DSM - Digital Surface Model, the elevation includes the structures above the surface, for example, buildings, trees, bridges.
matching_method	Optional string. The method used to generate 3D points. ETM-A feature-based stereo matching that uses the Harris operator to detect feature points. It is recommended for DTM generation. SGM- Produces more points and more detail than the ETM method. It is suitable for generating a DSM for urban areas. This is more computationally intensive than the ETM method1. MVM (Multi-view image matching (MVM) - is based on the SGM matching method followed by a fusion step in which the redundant depth estimations across single stereo model are merged. It produces dense 3D points and is computationally efficient References: Heiko Hirschmuller et al., “Memory Efficient Semi-Global Matching,” ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume 1-3, (2012): 371-376. Refer to the documentation of “matching_method” parameter of the Generate Point Cloud GP tool
context	Optional dictionary. Additional allowed point cloud generation parameter and DEM interpolation parameter can be assigned here. For Example: Point cloud generation parameters - {“maxObjectSize”: 50, “groundSpacing”: None, “minAngle”: 10, “maxAngle”: 70, “minOverlap”: 0.6, “maxOmegaPhiDif”: 8, “maxGSDDif”: 2, “numImagePairs”: 2, “adjQualityThreshold”: 0.2, “regenPointCloud”: False } DEM interpolation parameters - {“method”: “TRIANGULATION”, “smoothingMethod”: “GAUSS5x5”, “applyToOrtho”: True, “fillDEM”: “`https://....`” } Note: The “applyToOrtho” flag can apply the generated DEM back into the mosaic dataset’s geometric function to achieve more accurate orthorectification result. The “fillDEM” flag allows the user to specify an elevation service URL as background elevation to fill the area when elevation model pixels cannot be interpolated from the point cloud.
gis	Optional `GIS` . The GIS on which this tool runs. If not specified, the active GIS is used.

Returns: The DEM layer item

generate_orthomosaic¶

arcgis.raster.orthomapping.generate_orthomosaic(image_collection, out_ortho, regen_seamlines=True, recompute_color_correction=True, context=None, *, gis=None, future=False, **kwargs)¶

Function can be used for generating single ortho-rectified mosaicked image from image collection after the block adjustment.

Parameter	Description
image_collection	Required. The input image collection that will be used to generate the ortho-mosaic from. The image_collection can be a portal Item or an image service URL or a URI The image_collection must exist.
out_ortho	Required. This is the ortho-mosaicked image converted from the image collection after the block adjustment. It can be a url, uri, portal item, or string representing the name of output dem (either existing or to be created.) Like Raster Analysis services, the service can be an existing multi-tenant service URL.
regen_seamlines	Optional, boolean. Choose whether to apply seamlines before the orthomosaic image generation or not. The seamlines will always be regenerated if this parameter is set to True. The user can set the seamline options through the context parameter. If the seamline generation options are not set, the default will be used. Default value is True
recompute_color_correction	Optional, boolean. Choose whether to apply color correction settings to the output ortho-image or not. Color correction will always be recomputed if this option is set to True. The user can configure the compute color correction settings through the context parameter. If there is no color collection setting, the default will be used. Default value is True
context	Optional dictionary. Context contains additional environment settings that affect output image. The supported environment settings for this tool are: Output Spatial Reference (outSR)-the output features will be projected into the output spatial reference. Extent (extent) - extent that would clip or expand the output image Cell Size (cellSize) - The output raster will have the resolution specified by cell size. Compute Seamlines (seamlinesMethod) - Default. Clipping Geometry (clippingGeometry) - Clips the orthomosaic image to an area of interest defined by the geometry. Orthomosaic As Overview (orthoMosaicAsOvr) - Adds the orthomosaic as an overview of the image collection. Compute Color Correction (colorcorrectionMethod) — Default. Example: { “outSR”: {“wkid”: 3516}, “extent”: {“xmin”: 470614.263139, “ymin”: 8872849.409968, “xmax”: 532307.351827, “ymax”: 8920205.372412, “spatialReference”: {“wkid”: 32628}}, “clippingGeometry”: {}, “orthoMosaicAsOvr”: False, “seamlinesMethod”: “VORONOI”, “minRegionSize”: 100, “pixelSize”: “”, “blendType”: “Both”, “blendWidth”: None, “blendUnit”: “Pixels”, “requestSize”: 1000, “minThinnessRatio”: 0.05, “maxSliverSize”: 20 “colorCorrectionMethod”: “DODGING”, “dodgingSurface”: “Single_Color”, “referenceImg”: {“url”: “`https://...`”}, “skipRows”: 10, “skipCols”: 10, “reCalculateSats”: “OVERWRITE” }
gis	Optional `GIS` . The GIS on which this tool runs. If not specified, the active GIS is used.

Returns: The Orthomosaicked Imagery layer item

generate_report¶

arcgis.raster.orthomapping.generate_report(image_collection, report_format='PDF', *, gis=None, future=False, **kwargs)¶

This function is used to generate orthomapping report with image collection that has been block adjusted. The report would contain information about the quality of the adjusted images, the distribution of the control points, etc. The output of this service tool is a downloadable html page.

Parameter	Description
image_collection	Required. The input image collection that should be used to generate a report from. The image_collection can be a portal Item or an image service URL or a URI The image_collection must exist.
report_format	Type of the format to be generated. Possible PDF, HTML. Default - PDF
gis	Optional `GIS` . The GIS on which this tool runs. If not specified, the active GIS is used.

Returns: The URL of a single html webpage that is a formatted orthomapping report

query_camera_info¶

arcgis.raster.orthomapping.query_camera_info(camera_query=None, *, gis=None, future=False, **kwargs)¶

This service tool is used to query specific or the entire digital camera database. The digital camera database contains the specs of digital camera sensors that were used to capture drone images.

Parameter

Description

camera_query

Required String. This is a SQL query statement that can be used to filter a portion of the digital camera database. Digital camera database can be queried using the fields Make, Model, Focallength, Columns, Rows, PixelSize.

Example:

“Make=’Rollei’ and Model=’RCP-8325’”

gis

Optional GIS . The GIS on which this tool runs. If not specified, the active GIS is used.

Returns: Data Frame representing the camera database

query_control_points¶

arcgis.raster.orthomapping.query_control_points(image_collection, query, *, gis=None, future=False, **kwargs)¶

Query for control points in an image collection. It allows users to query among certain control point sets that has ground control points inside.

Parameter	Description
image_collection	Required, the input image collection on which to query the the control points. The image_collection can be a portal Item or an image service URL or a URI. The image_collection must exist.
query	Required string. a SQL statement used for querying the point; Example: “pointID > 100”
gis	Optional `GIS` . The GIS on which this tool runs. If not specified, the active GIS is used.

Returns: A dictionary object

reset_image_collection¶

arcgis.raster.orthomapping.reset_image_collection(image_collection, *, gis=None, future=False, **kwargs)¶

Reset the image collection. It is used to reset the image collection to its original state. The image collection could be adjusted during the orthomapping workflow and if the user is not satisfied with the result, they will be able to clear any existing adjustment settings and revert the images back to un-adjusted state

Parameter

Description

image_collection

Required, the input image collection to reset The image_collection can be a portal Item or an image service URL or a URI.

The image_collection must exist.

gis

Optional GIS . The GIS on which this tool runs. If not specified, the active GIS is used.

Returns: A boolean indicating whether the reset was successful or not

compute_spatial_reference_factory_code¶

arcgis.raster.orthomapping.compute_spatial_reference_factory_code(latitude, longitude)¶

Computes spatial reference factory code. This value may be used as out_sr value in create image collection function

Parameter	Description
latitude	latitude value in decimal degrees that will be used to compute UTM zone
longitude	longitude value in decimal degrees that will be used to compute UTM zone

Returns: factory_code : spatial reference factory code