How to set spacing of PNGs for length measuring

[RLeipe]

I want to use the Ruler tool on PNGs, but cant't figure out how to set the spacing for a PNG so that the getWorldLength() function can work (If I even understood correctly how it works). How and where would I do this?

[ivmartel]

I created #897 to allow for manual calibration: for data that do not provide pixel spacing, the user should be able to specify it manually. The app should provide a setImageSpacing method that would set the spacing of the image. From then, the measuring tools should work.

[RLeipe]

Thanks, that's exactly it.

[RLeipe]

One thing I'm still not getting: When using the DWV Static on a png, using the ruler still results in "mm" being shown after the length (which seems to be just the number of pixels). Since the mm seems to only be displayed if there is a spacing set:

var length = line.getWorldLength(spacing.getColumnSpacing(), spacing.getRowSpacing());

if (length !== null) {quant.length = {value: length, unit: dwv.i18n('unit.mm')};}
There seems to be some way in which dwv static has made at least that work. How is that?

[ivmartel]

You're right, the code sets a default spacing for DOM images (see domReader.js#L45), which is wrong...

[ivmartel]

Closing for now, please comment on #897 if you need.