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Fix: Handle HGT void values (-32768) in bilinear and nearestNeighbour #34

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Fix: Handle HGT void values (-32768) in bilinear and nearestNeighbour #34

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36 changes: 33 additions & 3 deletions src/hgt.js
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,8 @@ var fs = require('fs'),
extend = require('extend'),
_latLng = require('./latlng');

var HGT_VOID = -32768;

function Hgt(path, swLatLng, options) {
var fd = fs.openSync(path, 'r'),
stat;
Expand Down Expand Up @@ -31,7 +33,8 @@ function Hgt(path, swLatLng, options) {
}

Hgt.nearestNeighbour = function(row, col) {
return this._rowCol(Math.round(row), Math.round(col));
var elevation = this._rowCol(Math.round(row), Math.round(col));
return elevation === HGT_VOID ? null : elevation;
};

Hgt.bilinear = function(row, col) {
Expand All @@ -48,8 +51,27 @@ Hgt.bilinear = function(row, col) {
v10 = this._rowCol(rowLow, colHi),
v11 = this._rowCol(rowHi, colHi),
v01 = this._rowCol(rowHi, colLow),
v1 = avg(v00, v10, colFrac),
v1, v2;

if (v00 !== HGT_VOID && v10 !== HGT_VOID) {
v1 = avg(v00, v10, colFrac);
} else if (v00 !== HGT_VOID) {
v1 = v00;
} else if (v10 !== HGT_VOID) {
v1 = v10;
} else {
v1 = null;
}

if (v01 !== HGT_VOID && v11 !== HGT_VOID) {
v2 = avg(v01, v11, colFrac);
} else if (v01 !== HGT_VOID) {
v2 = v01;
} else if (v11 !== HGT_VOID) {
v2 = v11;
} else {
v2 = null;
}

// console.log('row = ' + row);
// console.log('col = ' + col);
Expand All @@ -66,7 +88,15 @@ Hgt.bilinear = function(row, col) {
// console.log('v1 = ' + v1);
// console.log('v2 = ' + v2);

return avg(v1, v2, rowFrac);
if (v1 !== null && v2 !== null) {
return avg(v1, v2, rowFrac);
} else if (v1 !== null) {
return v1;
} else if (v2 !== null) {
return v2;
} else {
return null;
}
};

Hgt.prototype.destroy = function() {
Expand Down