stravify-app/poly.html at main · thomasht86/stravify-app · GitHub

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<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>Encoded Polyline Viewer (Equirectangular)</title>
  <style>
    body{font-family:Arial, sans-serif; margin:20px; text-align:center;}
    #canvas{border:1px solid #ccc;}
    textarea{width:100%; height:120px; font-family:monospace;}
    button{padding:10px 20px; margin-top:10px; font-size:16px; cursor:pointer;}
    label{font-weight:bold;}
  </style>
</head>
<body>
  <h2>Encoded Polyline → Equirectangular Square</h2>
  <p>Paste an encoded polyline string below (it can include newlines, JSON escapes, etc.).<br>
     <small>Separate multiple polylines with a blank line or a semicolon “;”.</small></p>
  <label for="polyline">Polyline input</label><br>
  <textarea id="polyline" spellcheck="false" wrap="off" placeholder="_p~iF~ps|U_ulLnnqC …"></textarea><br/>
  <button id="drawBtn">Draw</button>
  <br><br>
  <canvas id="canvas" width="500" height="500"></canvas>
  <script>
    /* =============================================================
       0 · Helpers: JSON‑style unescape without eval
    ============================================================= */
    function unescapeJSON(raw){
      // Try JSON.parse trick to handle \" \u2022 etc.
      try{
        return JSON.parse('"'+ raw.replace(/"/g,'\\"') +'"');
      }catch(e){
        return raw; // if it fails, keep original
      }
    }

    /* =============================================================
       1 · Parse user input  ⟶  array of raw encoded strings
    ============================================================= */
    function parseInput(text){
      // Normalise line endings
      text = text.replace(/\r\n?/g,'\n');
      // If user explicitly uses semicolon, split there
      if(text.includes(';')){
        return text.split(';').map(s=>s.trim()).filter(Boolean);
      }
      // If there is a blank line (double newline) -> treat each block as separate polyline
      if(/\n\s*\n/.test(text)){
        return text.split(/\n\s*\n/).map(s=>s.replace(/\s+/g,'').trim()).filter(Boolean);
      }
      // Otherwise treat everything as ONE polyline: just remove whitespace
      return [text.replace(/\s+/g,'')];
    }

    /* =============================================================
       2 · Polyline decoder (Google algorithm)
    ============================================================= */
    function decodePolyline(str){
      let index = 0, lat = 0, lng = 0, points = [];
      const len = str.length;
      while(index < len){
        let b, shift = 0, result = 0;
        // latitude
        do{
          b = str.charCodeAt(index++) - 63;
          if(b < 0) return []; // invalid char – give up on this string
          result |= (b & 0x1f) << shift;
          shift += 5;
        }while(b >= 0x20 && index < len);
        lat += ((result & 1) ? ~(result >> 1) : (result >> 1));
        // longitude
        shift = 0; result = 0;
        do{
          b = str.charCodeAt(index++) - 63;
          if(b < 0) return [];
          result |= (b & 0x1f) << shift;
          shift += 5;
        }while(b >= 0x20 && index < len);
        lng += ((result & 1) ? ~(result >> 1) : (result >> 1));
        points.push([lat * 1e-5, lng * 1e-5]);
      }
      return points;
    }

    /* =============================================================
       3 · Projection helpers
    ============================================================= */
    function centroid(all){
      let sLat=0, sLon=0, n=0;
      all.forEach(pts=>pts.forEach(p=>{sLat+=p[0]; sLon+=p[1]; n++;}));
      return {lat:sLat/n, lon:sLon/n};
    }
    function project(arr, c){
      const cos0 = Math.cos(c.lat*Math.PI/180);
      return arr.map(p=>{
        let dLon = p[1]-c.lon; if(dLon>180) dLon-=360; if(dLon<-180) dLon+=360;
        return [dLon*cos0, p[0]-c.lat];
      });
    }
    function fit(arrays, size){
      let minX=Infinity,minY=Infinity,maxX=-Infinity,maxY=-Infinity;
      arrays.forEach(a=>a.forEach(([x,y])=>{if(x<minX)minX=x;if(x>maxX)maxX=x;if(y<minY)minY=y;if(y>maxY)maxY=y;}));
      const scale = (size*0.9)/Math.max(maxX-minX,maxY-minY||1e-9);
      return arrays.map(a=>a.map(([x,y])=>[(x-(minX+maxX)/2)*scale+size/2,((y-(minY+maxY)/2)*-scale)+size/2]));
    }

    /* =============================================================
       4 · Canvas renderer (one path per polyline, break on jumps)
    ============================================================= */
    function draw(ctx, polys, size){
      ctx.clearRect(0,0,size,size);
      ctx.lineWidth=2; ctx.strokeStyle='#0074D9'; const breakDist=size*0.45;
      polys.forEach(arr=>{
        ctx.beginPath(); let prev=null;
        arr.forEach(([x,y])=>{
          if(!prev){ctx.moveTo(x,y); prev=[x,y]; return;}
          const d=Math.hypot(x-prev[0],y-prev[1]);
          if(d>breakDist) ctx.moveTo(x,y); else ctx.lineTo(x,y);
          prev=[x,y];
        });
        ctx.stroke();
      });
      ctx.fillStyle='red'; ctx.beginPath(); ctx.arc(size/2,size/2,4,0,Math.PI*2); ctx.fill();
    }

    /* =============================================================
       5 · UI bridge
    ============================================================= */
    const SIZE=500; const ctx=document.getElementById('canvas').getContext('2d');
    document.getElementById('drawBtn').addEventListener('click',()=>{
      const raw=document.getElementById('polyline').value;
      if(!raw.trim()){alert('Please paste an encoded polyline'); return;}

      // Step 1: break into candidate strings
      const blocks=parseInput(raw);
      // Step 2: JSON‑style unescape each (handles double‑backslashes, \uXXXX, etc.)
      const clean=blocks.map(unescapeJSON);
      // Step 3: decode – if a block fails, skip it
      const decoded=clean.map(decodePolyline).filter(p=>p.length);
      if(!decoded.length){alert('None of the strings looked like a valid polyline.'); return;}
      // Step 4: projection + drawing
      const cen=centroid(decoded);
      const proj=decoded.map(p=>project(p,cen));
      const pixel=fit(proj,SIZE);
      draw(ctx,pixel,SIZE);
    });

    // preload demo example
    document.getElementById('polyline').value =
      `_p~iF~ps|U_ulLnnqC\n_mqNvxq@`;
  </script>
</body>
</html>