ArcObjects Library Reference (Geometry)

# ISpatialReferenceResolution.ConstructFromHorizon Method

Defines the XY resolution and domain extent of this spatial reference based on the extent of its horizon. Low precision SRs will have minimum resolution of 1/10mm in current units.

```[Visual Basic .NET]
Public Sub ConstructFromHorizon ( _
)```
```[C#]
public void ConstructFromHorizon (
);```
```[C++]
HRESULT ConstructFromHorizon(
void
);```

#### Product Availability

Available with ArcGIS Engine, ArcGIS Desktop, and ArcGIS Server.

#### Remarks

ConstructFromHorizon defines a domain extent and resolution sufficient to cover the horizon of a given coordinate system for high precision spatial references.  For low-precision spatial references the domain extent is centered on the horizon center. It does not define an extent for the Z- or M-domains; for these use methods available on ISpatialReference.

Projected Coordinate Systems

For a high precision ProjectedCoordinateSystem (PCS), ConstructFromHorizon defines the domain extent to be a square completely covering, and slightly larger than, the horizon extent of the PCS (which is an arbitrary rectangle). The scale factor (1/precision) is chosen to fit this domain.

For a low precision PCS, the center of the domain extent is aligned with the center of the horizon extent and expanded to achieve a target resolution of 1mm.

The example below lists high and low precision extents for WGS 1984 UTM Zone 11N.

Name Low Precision ProjectedCoordinateSystem High Precision ProjectedCoordinateSystem
MinX -573,741.824 -5,120,900.0
MinY -1,073,741.824 -9,998,100.0
MaxX 1,573,741.823 14,875,300.0
MaxY 1,073,741.823 9,998,100.0
Resolution 0.001 2.2 x 10^-9

Geographic Coordinate Systems

For a high precision GeographicCoordinateSystem (GCS), ConstructFromHorizon produces the square domain (-400, -400, 400, 400) (expressed in the units of the SR).

For a low precision GCS the upper right hand corner is adjusted to achieve a default resolution of 1/500 of an arc-second.

Name Low Precision GeographicCoordinateSystem High Precision GeographicCoordinateSystem
MinX -400 -400
MinY -400 -400
MaxX 793.046469444444 400
MaxY 793.046469444444 400
Resolution 5.55555555555556E-07 (1/500 arc-second) 8.8 x 10^-14

Unknown Coordinate Systems

For an UnknownCoordinateSystem (UCS), the "horizon" is defined to be a square that produces a resolution of 1 millimeter for a low precision UCS or 1/10 mm for a high precision UCS.

The example below lists high and low precision extents for an UnknownCoordinateSystem.

Name Low Precision UnknownCoordinateSystem High Precision UnknownCoordinateSystem
MinX -1,073,741.8245 -450,359,962,737.05
MinY -1,073,741.8245 -450,359,962,737.05
MaxX 1,073,741.8225 450,359,962,737.049
MaxY 1,073,741.8225 450,359,962,737.049
Resolution 0.001 0.0001

ISpatialReferenceResolution Interface

#### .NET Snippets

Make Spatial Reference | Create High Precision Spatial Reference

#### .NET Samples

Create a custom raster type from the ground up for DMCII data (Code Files: DMCIIRasterType) | Creating a toolbar of globe tools (Code Files: SpatialReference)

#### .NET Related Topics

Constructing a high- or low-precision spatial reference | Creating feature classes | How to import or export a spatial reference | Working with GeometryEnvironment