Speed improvement for drawing smaller tiffs when zoomed in.

marcon2 commented 5 years ago

When using a high resolution (256, being 1 pixel rectangles if tiles are 256x256) and zooming in, rendering the georaster-layer becomes slow, taking a few seconds per redraw. For smaller TIFFs, too much computation is done, as at some moment each TIFF pixel will be painted as multiple pixels on the screen. And with resolution 256, each screen pixel is painted separately.

In that case, it would not need to compute each screen pixel anymore, but could revert to painting each TIFF pixel.

With this code fix, for 500x500 pixel TIFF the application then remains responsive.

Some counter-arguments could be:

Result may become a bit less accurate, due to rounding to integer pixel sizes.
For TIFFs that are not geo-rectified, using rectangular fill areas may also give a less accurate image than with computing each screen pixel individually. (not sure if the current code would support non-georectified tiffs by the way, I don't use that).

Some details for the attached code:

If I do not round the values in the fillRect call, I get stripes in the resulting image, probably because it is not painting on some pixels.
I round the pixel size using ceil, to be sure the rectangle is large enough to fit to the next rectangle, possibly overlapping 1 pixel.

DanielJDufour commented 5 years ago

I republished https://www.npmjs.com/package/georaster-layer-for-leaflet

marcon2 commented 5 years ago

Thanks again for the quick turn around.

Kind regards,

Marco Nijdam

Principal Consultant

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Van: Daniel J. Dufour notifications@github.com Verzonden: maandag 12 november 2018 16:27 Aan: GeoTIFF/georaster-layer-for-leaflet CC: Marco Nijdam; Author Onderwerp: Re: [GeoTIFF/georaster-layer-for-leaflet] Speed improvement for drawing smaller tiffs when zoomed in. (#9)

I republished https://www.npmjs.com/package/georaster-layer-for-leaflet

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GeoTIFF / georaster-layer-for-leaflet

Speed improvement for drawing smaller tiffs when zoomed in. #9