Support affine transforms in the proj4 string #986
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The latest version of proj4 supports affine transforms via parameters such as +s11 and +xoff. Proj4js doesn't yet support this, but since it is useful, implement these transforms. Strictly, in Proj4 6.0.0, you can specify an affine transform like so: `echo 1 2 | cs2cs +proj=affine +to +proj=affine +s11=1.046 +s12=0.0915 +s21=-0.0915 +s22=1.046 +xoff=-1054 +yoff=-1160`, where instead of a projection the `affine` transformation is specified. However, proj4js expects `+proj=` to be one of its known projections. Therefore, for know, a layer in image space coordinates could be transformed via something like `+proj=longlat +axis=enu +s11=1.046 +s12=-0.0915 +s21=0.0915 +s22=1.046 +xoff=-1054 +yoff=-1160`.
Along with the addition of proj4 affine transforms, this allows multiple tile layers to have different (and adjustable) transforms.
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This could be broken into two independent PRs if it preferred. It will allow support for overlaying multiple tile layers that are distorted compared to each other, for instance with microscopy images of multiple tissue slices. |
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Once this and PR #985 are merged, you can see an example use on a tutorial based on the deep zoom example. |
aashish24
approved these changes
Apr 3, 2019
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The latest version of proj4 supports affine transforms via parameters such as +s11 and +xoff. Proj4js doesn't yet support this, but since it is useful, implement these transforms.
Strictly, in Proj4 6.0.0, you can specify an affine transform like so:
echo 1 2 | cs2cs +proj=affine +to +proj=affine +s11=1.046 +s12=0.0915 +s21=-0.0915 +s22=1.046 +xoff=-1054 +yoff=-1160, where instead of a projection theaffinetransformation is specified. However, proj4js expects+proj=to be one of its known projections. Therefore, for know, a layer in image space coordinates could be transformed via something like+proj=longlat +axis=enu +s11=1.046 +s12=-0.0915 +s21=0.0915 +s22=1.046 +xoff=-1054 +yoff=-1160.Add the ability to easily set the tile layer's gcs. Along with the addition of proj4 affine transforms, this allows multiple tile layers to have different (and adjustable) transforms.
This is a better implementation of the old branch to add a matrix transform the proj4 string (ec462b5). This should eventually be able to transition to official support in proj4js.