Feature GeoTIFF

[ruffson]

Hi there,

this branch attempts to implement some support for geotiffs (#98). This can become quite involved and if we implement everything about geotiff, we end up with a re-implementation of gdal.
So instead, I wrote something that gets all of the missing geo data out of geotiffs.

Summary

• The missing tags are retrieved: ModelPixelScaleTag, ModelTransformationTag, ModelTiepointTag, GeoKeyDirectoryTag, GeoDoubleParamsTag, GeoAsciiParamsTag, GdalNodata.
• The data from the geokey directory (GeoKeyDirectoryTag) is read out and saved in a hashmap.
• All of the geotiff keys mentioned in the spec are defined in an enum which is the key for the hashmap

Open questions

• It has to be decided how the values are to be accessed from outside, so how to make the geokey dir data available. To me there are three possibilities: 1. just make the hashmap public, 2. return a copy of the hashmap or 3. Offer a method like the get_tag methods which returns an option of a value given a geokey key.
• I did not know how I can get the tags::Tag value so I can check for it in my for loop in geo_key.rs, e.g. instead of explicitely checking for a value of 34736 I would rather compare against Tag::GeoDoubleParamsTag as u16 but this does not work because of the tags! macro around the Tag enum.

Things to keep in mind

• I noticed that all my geotiff's ModelTiepointTag only contained one tiepoint, and that gdalinfo shows all 5 tie point maps (top right, top bottom, center, etc.). This is apparently calculated, so this needs to take into account, the ModelPixelScaleTag, the width and height of the raster image and the projection type. And then they must be calculating the other tie points by calculating raster points and then project those. I don't think it makes sense to implement that in this package (at this point anyways), to me this belongs more into a geo-tools package or something, which parses values from geotiff. I will have to implement this so I can report back at some point when I have something to show.

Please let me know what you guys think and what is missing.

[HeroicKatora]

I think it's too much in one PR. I'd rather merge the smaller features such as newly recognized tags and value types quickly and leave the mechanisms of parsing the types as a separate draft as everything involved needs quite a lot of polish and probably require a lot of extra work if it were to be maintenaned in the current state.

[ruffson]

I think it's too much in one PR. I'd rather merge the smaller features such as newly recognized tags and value types quickly and leave the mechanisms of parsing the types as a separate draft as everything involved needs quite a lot of polish and probably require a lot of extra work if it were to be maintenaned in the current state.

Okay I will then remove everything except for the types and tags and create another repo for my own use with the contents of the geo folder and do more parsing of the values, do projections, etc. there. I will look through your edits soon and make changes accordingly. Thank you for your review!

[HeroicKatora]

Sounds good. I do appreciate the work and would like to see it merged—or independently published—at some point. Don't hesitate to ask or propose additional interface in case something needs additional changes in tiff.

[ruffson]

I removed the geo stuff and put it in my own repository.

[ruffson]

Rebased.