publiclab/mapknitter

Calculate and display exported image dimensions from selected cm/px export resolutions

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#1,320 opened on May 24, 2020

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 (2 comments) (0 reactions) (0 assignees)Ruby (203 forks)auto 404
JavaScriptexportinghacktoberfesthelp wanted

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Description

Some maps are stalling and hitting on the right resolution isn't easy. See these 2 stalled maps:

image

Note we don't see output resolution until they're complete, and they probably crashed or stalled.

We should be able to calculate at least roughly what the output dimensions in pixels would look like for a given cm/px export, using the new cloud exporter.

Let's try to use the image collection bounds and the cm/px to estimate the output dimensions. We can even say that 10cm/px would result in HxW dimensions and 100 in HxW - in the dialog box where you enter the resolution.

Here is the calculation for x,y pixel dimensions in Ruby, from the exporter code:

https://github.com/publiclab/mapknitter-exporter/blob/db65afbbeccdecedc3c50fa43bbeea3103f3d546/lib/mapknitterExporter.rb#L66-L70

The full exact calculation can be found in this file, using the Proj4.js library to calculate latitude,longitude => x,y projection:

https://github.com/publiclab/image-sequencer-app/blob/fad302f2d15745414bb362f28806a8568b4001c3/src/api/v2/util/converter-multiSequencer.js#L53-L61

This code is a bit tangled up but we could pull out the relevant portions into a JS function that accepts scale and a set of lat/lon bounds, and outputs x,y dimensions. This would be a great first step!

Contributor guide

Research direction
Study the mapknitter exporter Ruby code to understand the pixel dimension calculation, then implement a similar JavaScript function using Proj4.js to compute output dimensions from lat/lon bounds and cm/px scale, and integrate it into the export dialog.
Tech stack
rubyjavascript
Domain
backendfrontend
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
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Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Mostly clear
Prerequisites
GitRubyJavaScript
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60