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Region and url finder for SRTM1
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function region (pt) { | |
var pt = pt, regions, r; | |
if (!Array.isArray(pt) || pt.length < 2) return false; | |
/* | |
* Boundaries of SRTM regions as lower left -> upper right: | |
* [[min lon,min lat], [max lon, max lat]] | |
* The records use lower left coordinates, so N37W123.hgt covers 37->38 lat, -123->-122 lon | |
* See: http://dds.cr.usgs.gov/srtm/version2_1/SRTM1/Region_definition.jpg | |
*/ | |
regions = r = [ | |
[[-126, 38], [-111, 50]], // region 1, Washington, Oregon etc | |
[[-111, 38], [-97, 50]], // 2 | |
[[-97, 38], [-83, 50]], // 3 | |
[[-123, 28], [-100, 38]], // 4 | |
[[-100, 25], [-83, 38]], // 5 | |
[[-83, 17], [-64, 48]], // 6 | |
[[-180, 0], [-129, 60]] // 7 | |
]; | |
var hit = 0; | |
function within (a,i) { | |
if (pt[0] >= r[i][0][0] && pt[0] < r[i][1][0]) { | |
if (pt[1] >= r[i][0][1] && pt[1] < r[i][1][1]) { | |
return hit = i + 1; | |
} | |
return false; | |
} | |
return false; | |
} | |
if (!r.some(within)) return false; | |
return hit; | |
} | |
function urlfor (pt) { | |
var r = region(pt); | |
if (!r) return false; | |
var baseUrl = "http://dds.cr.usgs.gov/srtm/version2_1/SRTM1/Region_0" | |
var lonPadded = parseInt(Math.ceil(Math.abs(pt[0]))).toString() | |
if (lonPadded.length < 3) lonPadded = '0'+lonPadded; | |
var hgt = 'N' + ~~pt[1] + 'W' + lonPadded + '.hgt.zip'; | |
return baseUrl + r + '/' + hgt; | |
} | |
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