# Find nearest vertex

Find the closest vertex and coordinate of a geometry to a point.

## Use case

Determine the shortest distance between a location and the boundary of an area. For example, developers can snap imprecise user clicks to a geometry if the click is within a certain distance of the geometry.

## How to use the sample

Click anywhere on the map. A magenta cross will show at that location. A blue circle will show the polygon's nearest vertex to the point that was clicked. A red diamond will appear at the coordinate on the geometry that is nearest to the point that was clicked. If clicked inside the geometry, the red and magenta markers will overlap. The information box showing distance between the clicked point and the nearest vertex/coordinate will be updated with every new location clicked.

## How it works

1. Get a `Geometry` and a `Point` to check the nearest vertex against.
2. Call `GeometryEngine.nearestVertex(inputGeometry, point)`.
3. Use the returned `ProximityResult` to get the `Point` representing the polygon vertex, and to determine the distance between that vertex and the clicked point.
4. Call `GeometryEngine.nearestCoordinate(inputGeometry, point)`.
5. Use the returned `ProximityResult` to get the `Point` representing the coordinate on the polygon, and to determine the distance between that coordinate and the clicked point.

## Relevant API

• GeometryEngine
• ProximityResult

The value of `ProximityResult.distance` is planar (Euclidean) distance. Planar distances are only accurate for geometries that have a defined projected coordinate system, which maintain the desired level of accuracy. The example polygon in this sample is defined in California State Plane Coordinate System - Zone 5 (WKID 2229), which maintains accuracy near Southern California. Accuracy declines outside the state plane zone.

## Tags

analysis, coordinate, geometry, nearest, proximity, vertex

## Sample Code

MainActivity.kt
Use dark colors for code blocksCopy
``````/* Copyright 2022 Esri
*
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*
* Unless required by applicable law or agreed to in writing, software
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
*
*/

package com.esri.arcgismaps.sample.findnearestvertex

import android.os.Bundle
import android.util.Log
import android.view.View
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity
import androidx.constraintlayout.widget.ConstraintLayout
import androidx.databinding.DataBindingUtil
import androidx.lifecycle.lifecycleScope
import com.arcgismaps.ApiKey
import com.arcgismaps.ArcGISEnvironment
import com.arcgismaps.Color
import com.arcgismaps.geometry.GeometryEngine
import com.arcgismaps.geometry.Point
import com.arcgismaps.geometry.Polygon
import com.arcgismaps.geometry.PolygonBuilder
import com.arcgismaps.geometry.SpatialReference
import com.arcgismaps.mapping.ArcGISMap
import com.arcgismaps.mapping.layers.FeatureLayer
import com.arcgismaps.mapping.symbology.SimpleFillSymbol
import com.arcgismaps.mapping.symbology.SimpleFillSymbolStyle
import com.arcgismaps.mapping.symbology.SimpleLineSymbol
import com.arcgismaps.mapping.symbology.SimpleLineSymbolStyle
import com.arcgismaps.mapping.symbology.SimpleMarkerSymbol
import com.arcgismaps.mapping.symbology.SimpleMarkerSymbolStyle
import com.arcgismaps.mapping.view.Graphic
import com.arcgismaps.mapping.view.GraphicsOverlay
import com.arcgismaps.portal.Portal
import com.arcgismaps.mapping.PortalItem
import com.esri.arcgismaps.sample.findnearestvertex.databinding.ActivityMainBinding
import kotlinx.coroutines.launch

class MainActivity : AppCompatActivity() {

// set up data binding for the activity
private val activityMainBinding: ActivityMainBinding by lazy {
DataBindingUtil.setContentView(this, R.layout.activity_main)
}

private val mapView by lazy {
activityMainBinding.mapView
}

private val distanceLayout: ConstraintLayout by lazy {
activityMainBinding.distanceLayout
}

private val vertexDistanceTextView: TextView by lazy {
activityMainBinding.vertexDistanceTextView
}

private val coordinateDistanceTextView: TextView by lazy {
activityMainBinding.coordinateDistanceTextView
}

// California zone 5 (ftUS) state plane coordinate system.
private val statePlaneCaliforniaZone5SpatialReference = SpatialReference(2229)

// create graphics with symbols for tapped location, nearest coordinate, and nearest vertex
private val tappedLocationGraphic =
Graphic(symbol = SimpleMarkerSymbol(SimpleMarkerSymbolStyle.X, Color.magenta, 15f))

// create graphic symbol of the nearest coordinate
private val nearestCoordinateGraphic =
Graphic(symbol = SimpleMarkerSymbol(SimpleMarkerSymbolStyle.Diamond, Color.red, 10f))

// create graphic symbol of the nearest vertex
private val nearestVertexGraphic =
Graphic(symbol = SimpleMarkerSymbol(SimpleMarkerSymbolStyle.Circle, Color.blue, 15f))

override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)

// authentication with an API key or named user is
// required to access basemaps and other location services
ArcGISEnvironment.apiKey = ApiKey.create(BuildConfig.API_KEY)

// create a polygon geometry
val polygon = PolygonBuilder(statePlaneCaliforniaZone5SpatialReference) {
}.toGeometry()
// set up the outline and fill color of the polygon
val polygonOutlineSymbol = SimpleLineSymbol(SimpleLineSymbolStyle.Solid, Color.green, 2f)
val polygonFillSymbol = SimpleFillSymbol(
SimpleFillSymbolStyle.ForwardDiagonal,
Color.green,
polygonOutlineSymbol
)
// create a polygon graphic
val polygonGraphic = Graphic(polygon, polygonFillSymbol)
// create a graphics overlay to show the polygon, tapped location, and nearest vertex/coordinate
val graphicsOverlay = GraphicsOverlay(
listOf(
polygonGraphic,
tappedLocationGraphic,
nearestCoordinateGraphic,
nearestVertexGraphic
)
)

// create a map using the portal item
val map = ArcGISMap(statePlaneCaliforniaZone5SpatialReference)
val portal = Portal("https://arcgisruntime.maps.arcgis.com")
val portalItem = PortalItem(portal, "99fd67933e754a1181cc755146be21ca")
val usStatesGeneralizedLayer = FeatureLayer.createWithItemAndLayerId(portalItem, 0)
// and add the feature layer to the map's operational layers
// add the map to the map view
mapView.map = map
// add the graphics overlay to the map view
lifecycleScope.launch {
// check if map has loaded
// zoom to the polygon's extent
mapView.setViewpointGeometry(polygon.extent, 100.0)
// get point on map tapped
mapView.onSingleTapConfirmed.collect { event ->
// find nearest vertex on map tapped
event.mapPoint?.let { findNearestVertex(it, polygon) }
}
}.onFailure {
}
}
}

/**
* Finds the nearest vertex from [mapPoint] from the [polygon]
*/
private fun findNearestVertex(mapPoint: Point, polygon: Polygon) {
// show where the user clicked
tappedLocationGraphic.geometry = mapPoint
// use the geometry engine to get the nearest vertex
val nearestVertexResult =
GeometryEngine.nearestVertex(polygon, mapPoint)
// set the nearest vertex graphic's geometry to the nearest vertex
nearestVertexGraphic.geometry = nearestVertexResult?.coordinate
// use the geometry engine to get the nearest coordinate
val nearestCoordinateResult =
GeometryEngine.nearestCoordinate(polygon, mapPoint)
// set the nearest coordinate graphic's geometry to the nearest coordinate
nearestCoordinateGraphic.geometry = nearestCoordinateResult?.coordinate
// show the distances to the nearest vertex and nearest coordinate
distanceLayout.visibility = View.VISIBLE
// convert distance to miles
val vertexDistance = ((nearestVertexResult?.distance)?.div(5280.0))?.toInt()
val coordinateDistance = ((nearestCoordinateResult?.distance)?.div(5280.0))?.toInt()
// set the distance to the text views
vertexDistanceTextView.text = getString(R.string.nearest_vertex, vertexDistance)
coordinateDistanceTextView.text =
getString(R.string.nearest_coordinate, coordinateDistance)

}

private val Color.Companion.blue: Color
get() {
return fromRgba(0, 0, 255, 255)
}

private val Color.Companion.magenta: Color
get() {
return fromRgba(255, 0, 255, 255)
}

private fun showError(message: String) {
Log.e(localClassName, message)
Snackbar.make(mapView, message, Snackbar.LENGTH_SHORT).show()
}
}``````