In neogeomat/OSMTT: Get a version of OSM data in previous time

This vignettes consists of

• 1. Introduction
• 2. Attic Functions
• 3. Classes and methods
• 4. How to use
• 5. Future work

1. Introduction {ch1}

OSM Overpass Api supports query for attic data but this feature has not been implemented in R. This issue is discovered here. This package is made with intention of extending the Osmdata package with the attic functions. It has 2 classes to handle attic data osmtt and osmttdiff. Osmtt represents data from a previous timestamp and osmttdiff represents changes in data between the given time frame.

2. Attic Functions {ch2}

Attic settings in overpass-api are date,diff and adiff. date returns results based on the OpenStreetMap database as of the date specified. Diff lets the database determine the difference of two queries at different points in time. Adiff is same like diff, but for all elements that aren't contained in the newer result, it is indicated what happened to them. In this package add_date and add_adiff, are implemented. diff is omitted since adiff gives more details than diff.

3. Classes and methods

Class:

1. osmtt

osmtt adds datetime parameters to overpass_query class which is then passed onto the actual query. The return from overpass_query and osmtt has the same structure so osmtt works similar to overpass_query. A bug in the osmdata package was found during this implementation. It has been fixed and pull request has been sent.

Methods

• print: Print returns the overpass query string from the object, it can be passed to overpass-api from browser too.
• plot: Plots the points and lines from osmdata object
• osmtt_sf: queries overpass object and converts to osmdata object

2. osmttdiff

osmttdiff handles the diff results from adiff setting. It separates elements according to create, modify and delete actions. Also it separates the new and old ones.

Methods

• print:
• osmttdiff_sf: Converts overpass diff xml to osmttdiff object

4. How to use

Attic data may not be supporeted by all overpass servers. First step is to find one which can handle the query.

# new_url <- "http://overpass-api.de/api/interpreter"
# osmdata::set_overpass_url(new_url)

To get the instance of osm database at a previous version in time, Use osmtt.

Specify place and time and form a query object. Place can bbox object or character, if character result from nominatim is used. Time must be in %Y-%m-%dT%H:%M:%SZ format e.g. 2019-01-01T12:00:00Z

# op <- osmtt("sudal nepal","2019-01-01T12:00:00Z")

Convert it to osmdata_sf object from osmdata package.

# op_sf <- osmtt_sf(op)

Other formats can also be used by directly using the osmdata package methods

# osmdata::osmdata_sp(op)
# osmdata::osmdata_xml(op)

To get the difference of osm database between two time, Use osmttdiff.

Specify place, oldtime and newtime and form query object. Newtime is optional. If omitted, current time is used for newtime.

# od<-osmadiff("sanga","2019-01-01T12:00:00Z")

Query overpass and get xml data

# odd<-osmdata:::overpass_query(osmdata::opq_string(od))

Convert overpass diff xml to osmttdiff object

# odd_sf <- osmttdiff_sf(odd) 

(Note: Queries are commented because query quota was exceeded)

5. Issues, Challenges and Further Works

5.1 Issues:

• When overpass api is busy, osmttdiff does not handle wait and retry.
• osmtt uses native call to C for parsing in osmtt_sf, but is not available in osmttdiff. Hence osmttdiff processing is slower.
• Writing xml output to file is supported but reading from xml has not been implemented
• osmttdiff sometimes gives node can not be found error. Source and solution of this is not found. This issue is shown here.
• In osmttdiff_sf direct call to rcpp_osmdata_sf of osmdata has been made. This is a design issue, but since it calls C interface, similar implementation could not be done through R.

5.2 Challenges

• Bugs in the dependency gave unexpected results, which took much time to figure and solve.
• Running out of api query quota for overpass-api
• Some code were in cpp. Knowledge on this part was limited
• Documentation on adiff format is limited

5.3 Further Works

• Visualization of changes
• Integration of osmtt and osmttdiff for piping
• Remove direct calls to dependency methods

neogeomat/OSMTT documentation built on Aug. 10, 2019, 11:22 a.m.