Post) How to Select a circular area in Application Development of ArcIMS?

Content summary

In the Application Development of ArcIMS-based Web GIS, whether through HTML Viewer, ActiveX Connector or Java Connector, we often need to provide circular selection tools, select any center and radius on the map, and then find the elements in a layer within the circular area. In this case, because the circle center is not from a point layer, and this circle is not generated by the point elements in the layer through the buffer, therefore, the Buffer function provided by ArcIMS cannot be called directly. In this case, we can adopt other alternatives.

Process description

In this article, we use the inner Polygon method of the circle. The principle is to generate a 48-side Inner Shape close to the Circle Based on the provided center and radius, and then use this polygon object and Filter to query the space. Of course, the closer the number of edges of the inner polygon is to the circle, the more accurate the query result is. The sample code is as follows: // Java Public Polygon createCirlePolygon (Point pnt, double dRadius ){ Double sineTheta, cosineTheta, twoPi; Int numPoints = 48; // Number of edges of the inner Polygon Polygon poly = new Polygon (); Points pnts = new Points (); TwoPi = 3.1415*2.0; // Create a polygon For (int I = 0; I <numPoints; I ++ ){ Point cpt = new Point (); SineTheta = Math. sin (twoPi * (I * 1.0/numPoints )); CosineTheta = Math. cos (twoPi * (I * 1.0/numPoints )); Cpt. setX (pnt. getX () + dRadius * cosineTheta ); Cpt. setY (pnt. getY () + dRadius * sineTheta ); Pnts. addPointObject (cpt ); } Pnts. addPointObject (pnts. getPointObject (0 )); Ring ring = new Ring (); Ring. setPoints (pnts ); Poly. addRing (ring ); Return poly; } // ASP. NET Public imspolympus Gon createCirlePolygon (IMSPoint pnt, double dRadius) { Imspolympus Gon poly = new imspolympus Gon (); Double sineTheta, cosineTheta, twoPi; Int numPoints = 48; // Number of edges of the inner Polygon IMSPoints pnts = new IMSPoints (); TwoPi = 3.1415*2.0; // Create a polygon For (int I = 0; I <numPoints; I ++) { IMSPoint cpt = new IMSPoint (); SineTheta = Math. Sin (twoPi * (I * 1.0/numPoints )); CosineTheta = Math. Cos (twoPi * (I * 1.0/numPoints )); Cpt. X = (pnt. X + dRadius * cosineTheta ); Cpt. Y = (pnt. Y + dRadius * sineTheta ); Pnts. Add (cpt ); } Pnts. Add (pnts [0]); IMSParts parts = new IMSParts (); Parts. Add (pnts ); Poly. Parts = parts; Return poly; }