GeoTiff: get actual values for min/max/nodata/name per band

Is your feature request related to a problem? Please describe. I’d like to know whether an alpha band has been added to the GeoTiff bands or not. I see that there is a property addAlpha_, but this sounds like a private property and not a public API.

Describe the solution you’d like I’m wondering whether it would be good to add a public API method such as hasAlphaBand() that simply returns this.addAlpha_? Happy to create a PR if that’s they way to go, but also open to other solutions. Maybe I’m missing something, too.

[ahocevar]

@m-mohr Sorry for the premature reply, you’re absolutely right that the nodata value can also be set from the geotiff.js image’s getGDALNoData() method.

I agree it does make sense to be able to access the nodata values. But for use in an application, it is not only enough to know the nodata value, but also the band index that holds it. So to come up with a meaningful API here, it would be good to know a bit more about your use case. Do you need the nodata value for the layer style, or for something completely different?

[m-mohr]

@ahocevar Yes, such a data object would help a lot.

I don’t specify any information in the source info right now (except normalize: false and the URL of the source). What I do then is to apply styling once I know the min/max values, basically doing linear stretching. no-data “styling” I also tried to do, but that did not work yet (i.e. something like if band value matches no-data value then 0, else 1). But I run into some issues with that approach, which I could not really debug yet (how to debug the styling expressions?). For some files the styling approach works, for some not (yet?).

I’m also stumbling across some parts of the documentation, where I’m not sure they are always correct. For example, in https://openlayers.org/en/latest/apidoc/module-ol_style_expressions.html#~ExpressionValue it says the value you get for bands is 0…1, but is that also the case if normalize is false? And what exactly does convertToRGB do… it makes it work for grayscale, but then fails for me when I’m loading RGB files, which is weird because I’d assume converting from RGB to RGB would basically do nothing. 😃 But I’m slowly digging deeper…