Go to content Go to navigation and search


Current SQL Server Blog Articles

    SQL Server Spatial: STFlipVectors
    SQL Server Spatial: Extract LineStrings in GeometryCollection to create LineString
    SQL Server Spatial: Converting a LineString to COGO XML
    SQL Server Spatial: Creating (Multi)LineStrings geometries from COGO XML instructions
    New Version of Package of TSQL Spatial Functions
    Vectorize/Segmentize SQL Server 2012
    Coordinate Editing Functions for SQL Server Spatial
    Function to Scale a geometry object for SQL Server Spatial
    TSQL String Tokenizer Function for SQL Server
    geography/geometry to MBR helper functions
    generate_series for SQL Server 2008
    Extract Polygons from result of STIntersection in SQL Server Spatial
    Function to round ordinates of a SQL Server Spatial geometry object
    Extract elements of SQL Server Spatial geometry object
    Counting number of polygon rings SQL Server Spatial
    Filtering Polygon Rings in SQL Server Spatial
    Function to Move a geometry object in SQL Server Spatial
    Alternate Centroid Functions for SQL Server Spatial
    Function to Rotate geometry objects in SQL Server Spatial
    A GetVertices wrapper for DumpPoints in SQL Server 2008 Spatial
    Creating a Morton number Space Key generator for SQL Server
    Gridding a geometry or geography object (SQL Server Denali)
    On hinting spatial indexes
    Random Search Procedure (SQL Server 2008 Spatial)
    COGO: Converting (Google Earth) Formatted Longitude/Latitude points to decimal degrees (SQL Server)
    COGO: Convert Degrees, Minutes and Seconds values to Decimal Degrees
    COGO: DD2DMS Formatting a latitude/longitude decimal degree value
    COGO: Create point from bearing and distance
    COGO: Compute number of vertices required to stroke circle or circular arc
    COGO: Calculating the bearing between two points (SQL Server 2008 Spatial)
    COGO: Compute arc length subtended by angle centre of circle
    COGO: Compute chord length of segment of a circle (arc)
    COGO: Computing Arc To Chord (Arc2Chord) Separation
    COGO: Creating a stroked polygon from a circle's centre x,y and radius
    COGO: Finding centre and radius of a curve defined by three points: FindCircle function
    Identifying Tight Radius Curves sections within LineString geometry data
    Generating random point data for SQL Server 2008 Spatial
    New Presentation on Active (Searchable) Spatial Metadata for SQL Server 2008 Spatial and FreeText
    Checking is a column in a table or a view is of type geometry or geography
    Extracting geometry type string values from geometry/geography objects in SQL Server 2008 Spatial
    Vectorising geometry objects in SQL Server 2008
    MBR to geography/geometry helper functions
    Extracting geometry types from geometry/geography objects in SQL Server 2008
    Getting the number of coordinate dimensions of a geometry/geography object in SQL Server 2008
    A Dump Points Function for SQL Server 2008 Spatial
    toGeography and toGeography Conversion Functions for SQL Server 2008 Spatial
    Write text file with spatial data from SQL Server 2008
    Loading Shapefiles into Geography type column in SQL Server 2008
    Tip #6: Correcting invalid geometries
    Tip #5: Where or where has my little column gone
    Tip #4: What Coordinate System is that?
    Tip #3: What object is that?
    Tip #2: Spatial Indexing and Primary Keys
    Tip #1: SQL Server 2008 "Katmai" - Setting SRIDs



RSS / Atom

Email me


Creative Commons License
All Blog Articles, Data Models and Free Source Code by Simon Greener, The SpatialDB Advisor is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

COGO: Compute number of vertices required to stroke circle or circular arc

Friday May 06 2011 at 01:38

In working with circles or arc segments one needs to be able to do more than just calculate chordlengths, arclengths or arc2chord separations.

For example, in order to be able to convert circles and arcs to vertex-stroked polygons and vice versa one needs to be able to compute the number of vertices to place between the points that subtend an arc on the circumference. This is what this function does.

Note that I have a schema call cogo in which I create functions like this. You can use anything you like.

/* ----------------------------------------------------------------------------------------
* @function   : OptimalCircleSegments
* @precis     : Returns the optimal integer number of circle segments for given arc-to-chord
*               separation and radius
* @version    : 1.0
* @usage      : FUNCTION OptimalCircleSegments( @dRadius Float,
*                                               @dArcToChordSeparation Float)
*                        RETURNS INTEGER
*               eg select cogo.OptimalCircleSegments(10,0.01) as segments;
* @param      : @dRadius                 : Radius of Circle
* @paramtype  : @dRadius                 : Float
* @param      : @dArcToChordSeparation   : Distance between the midpoint of the Arc and the Chord in metres
* @paramtype  : @dArcToChordSeparation   : Float
* @return     : OptimalCircleSegments    : the optimal number of segments
* @rtnType    : OptimalCircleSegments    : Integer
* @note       : Does not throw exceptions
* @note       : Assumes planar projection eg UTM.
* @history    : Simon Greener - Feb 2005 - Original coding.
Create Function [cogo].[OptimalCircleSegments](@p_dRadius               Float,
                                               @p_dArcToChordSeparation Float)
Returns Integer
      @dAngleRad              Float,
      @dCentreToChordMidPoint Float;
      IF ( @p_dRadius IS NULL OR
           @p_dArcToChordSeparation IS NULL )
          RETURN NULL;
      SET @dCentreToChordMidPoint = @p_dRadius - @p_dArcToChordSeparation;
      SET @dAngleRad              = 2 * aCos(@dCentreToChordMidPoint/==@==p_dRadius);
      Return CEILING( (2 * PI() ) / @dAngleRad );

Here is an example of how to use the function.

select cogo.OptimalCircleSegments(10,0.01) as segments;

I hope this is useful to someone.

Creative Commons License

post this at del.icio.uspost this at Diggpost this at Technoratipost this at Redditpost this at Farkpost this at Yahoo! my webpost this at Windows Livepost this at Google Bookmarkspost this to Twitter

Comment [1]

Can you correct “aCos(dCentreToChordMidPoint/====p_dRadius);” part of function…
Thanks alot…

— Kemal · 10 March 2014, 19:36 · #