How to draw Polyline without rendering map using coordinates-CodePudding

I have array of coordinates and I can draw polyline on map using theese coordinates without problem.

Now what I want to do is, only drawing a polyline to screen without rendering the map.

Below is first few items of my coordinates array:

[
            [6.56674, 45.39881],
            [6.56682, 45.399],
            [6.56701, 45.39959],
            [6.56727, 45.40006],
            [6.56738, 45.4003],
            [6.56745, 45.40041],
            [6.56757, 45.40053]
]

I want to draw the same polyline to black background without rendering map.

I tried to draw svg polyline using the array of coordinates but I couldn't achieved what I wanted only a dot appeared on the screen. Didn't draw a polyline.

import {Svg, Polyline} from 'react-native-svg';

<Svg height="100" width="100">
        <Polyline
          points={MY_ARRAY_OF_COORDS.map(item => `${item[0]},${item[1]`).join(" ")}
          fill="none"
          stroke="blue"
          strokeWidth="5"
          strokeLinecap="round"
          strokeLinejoin="round"
        />
</Svg>

CodePudding user response：

The <polyline> is actually rendered but almost invisible since the coordinates are very close to each other.

So you need to calculate a scale factor.

Js example

const coords= [
            [6.56674, 45.39881],
            [6.56682, 45.399],
            [6.56701, 45.39959],
            [6.56727, 45.40006],
            [6.56738, 45.4003],
            [6.56745, 45.40041],
            [6.56757, 45.40053]
];

//calculate coordinate range for a scale factor
let xArr = coords.map((val)=>{return val[0]} );
let xMin = Math.min(...xArr);
let xMax = Math.max(...xArr);
let yArr = coords.map((val)=>{return val[1]} );
let yMin = Math.min(...yArr);
let yMax = Math.max(...yArr);

let xRange = xMax- xMin;
let yRange = yMax- yMin;
let scale = 100/Math.max(...[xRange, yRange]);
//console.log(xRange, yRange, scale)


//scale coordinates
coords.forEach(function(coord){
  let [x,y] =[coord[0], coord[1]];
  coord[0] = (x-xMin)*scale;
  coord[1] = (y-yMin)*scale;
})

//draw polyline
const svg = document.querySelector('svg');
const polyline = svg.querySelector('polyline');
polyline.setAttribute('points', coords.join());

svg{
  border: 1px solid #ccc;
  overflow:visible
}

<svg height="100" width="100">
        <polyline
          points=""
          fill="none"
          stroke="blue"
          strokeWidth="10"
          strokeLinecap="round"
          strokeLinejoin="round"
        />
</svg>

First we need to calculate ranges for x and y values (so the maximum distances between maximum and minimum x).

let xRange = xMax- xMin; //0.000829999999999664
let yRange = yMax- yMin; //0.001720000000005939

If you need a svg bounding box of 100x100 units the scaling factor would be:

let scale = 100/Math.max(...[xRange, yRange]);

Eventually we need to subtract the minimum x and y offsets to align the polyline to the x/y axes origin.