msx/snapshort format without history

[indus]

Is there a way to use the msx snapshort format without the history but only output the last state? I would like to use it because I think it has a good ratio of speed and size for temporary data storage of processing steps.

Shapefiles and NDJSONs are bigger - only gz compression makes them smaller but also much slower to write and read.

-clean only-arcs helps to get rid of the data history when using a filter. but I don't know how to do the same for -simplify

[mbloch]

What mapshaper is saving is not exactly a history state. When you apply simplification, it's like adding a filter over the original vertices that can be removed or updated. When you export a snapshot after applying simplification, you're saving all the original vertices plus simplification threshold data for each vertex. The threshold data lets mapshaper change the amount of simplification on-the-fly, without recomputing anything.

I suspect that very few users expect to be able to undo simplification after re-importing a snapshot, so I'm tempted just to bake in the current simplification amount when you export a snapshot. I would leave the simplification data in the temporary snapshots that get made when you click "create a snapshot" under the ribbon menu, but remove the data when you export a snapshot.

I propose to also automatically remove the path data that you're currently deleting using -clean only-arcs. That data isn't recoverable anyway. Its only purpose is to enable paths removed by -filter to be displayed as ghosted lines.

Does this sound reasonable?

[mbloch]

You asked for a way to remove the data... yes there is. Some commands require that simplification be baked in before they can work. You can use -snap interval=0.

[indus]

your suggested changes would sound as they would indeed help. Just to clarify I would use the msx format in programmatic use. I would guess that ... -o tmp.msx would behave as an 'export' and not a 'temporary snapshot'.

Again - Thanks for your great work.

I will try baking the simplification with the -snap interval=0 for now.

[mbloch]

Yes, -o tmp.msx would behave like an export

[mbloch]

Just published v0.6.45, which includes the update that removes simplification data from snapshot files. This version doesn't clean up paths that were removed by -filter, -dissolve and several other commands. I'm thinking about removing those paths immediately after the commands are run, as opposed to when a snapshot is exported. As I mentioned earlier, I'm retaining them in order to display a ghosted image of the removed paths. I haven't found those images to be particularly useful. (If someone wants to compare the edited layer and the original layer, they can always use the + option to create a new output layer rather than replacing the original layer).

[indus]

Thank you. I hope nobody will miss this easy way to check the outcome of these operations.