alternative option for origin encoding missing

[zoot-inge]

in _parseTIFF code should be altered:
// http://geotiff.maptools.org/spec/geotiff2.7.html
// https://geotiffjs.github.io/geotiff.js/geotiffimage.js.html
// http://duff.ess.washington.edu/data/raster/drg/docs/geotiff.txt
if (meta.ModelTiepoint) {
var x_min = meta.ModelTiepoint[3];
var x_max = x_min + meta.ModelPixelScale[0]*meta.ImageWidth;
var y_min = meta.ModelTiepoint[4];
var y_max = y_min - meta.ModelPixelScale[1]*meta.ImageLength;
}
else if (meta.ModelTransformation) {
var x_min = meta.ModelTransformation[3];
var x_max = x_min + meta.ModelTransformation[0]*meta.ImageWidth;
var y_min = meta.ModelTransformation[7];
var y_max = y_min + meta.ModelTransformation[5]*meta.ImageLength;
}