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tmontaigu / shapefile-rs

Rust library to read & write shapefiles
MIT License
59 stars 19 forks source link

Not able to read feature metadata. #19

Closed xinaesthete closed 3 years ago

xinaesthete commented 3 years ago

I'm very new to Rust (somewhat experienced with GIS but it's not my main background), so apologies if there's something I just failed to grok properly.

I'm trying to read shapefiles with contour lines (from the Ordanance Survey Terr50 data FWIW), which are grouped into features with 2d coordinates and a 'PROP_VALUE' indicating the height of each line. I've previously been using https://github.com/calvinmetcalf/shapefile-js and wanted to experiment with porting that code to Rust / WASM.

In the context of shapefile.js, they parse the results into GeoJSON FeatureCollection, where each Feature has, in addition to geometry, a set of arbitrary properties indexed by string. So I access the height with feature.properties['PROP_VALUE'].

Reading through your documentation and code, I don't think I see anyway to do the equivalent with shapefile-rs, so I guess it's just a missing feature, but I could well have missed something.

xinaesthete commented 3 years ago

I see that you do have dbase::Record read from dbf, I think I'm on the right track now (a bit spoiled by shapefile.js being able to parse a zip directly, combining these elements appropriately).

tmontaigu commented 3 years ago

Hello,

In shapefile-rs, to access the properties associated to a geometry you first have to use Reader::iter_shapes_and_records to get an iterator that gives you both the shape (aka the geometry) and the record (aka the properties).

The record will be a hashmap that maps String to Values that you can use to get the values you want

xinaesthete commented 3 years ago

Indeed, I think I'd even looked at the method you mentioned before posting my initial message and then somehow it slipped my mind again. Many thanks for your help.

tmontaigu commented 3 years ago

Having the ability to read a shapefile directly from a zipfile could be a nice extra-feature, I'll look into adding that

xinaesthete commented 3 years ago

For now as a Rust-learning-exercise I'm fairly impressed by how easily opening a zip archive and processing the contents through your library is going with just a couple of extra lines of code, but it seems like it'd make sense for you to incorporate in a more comprehensive way to the library if you have time.