I’ve now uploaded to the Internet a little web-based program called GPX Reference Point Generator (GPXRPG).

GPXRPG may be of interest to the subset of OSM Contributors who use the OSM iD Editor for “armchair mapping”.

These Contributors add to the OSM database new Area features - particularly urban building footprints - by tracing the outline of each building on an aerial imagery background layer. Before commencing to trace new building outlines, they need to check that the aerial imagery background they have chosen is aligned to OSM’s coordinate system with sub-metre accuracy (and if not, adjust the alignment using the iD Editor’s Imagery Offset dialog).

Two items are required to provide a basis for the alignment check:

1. a “target spot” in the iD Editor’s Aerial Imagery Background Layer that has accurately known latitude-longitude coordinates. A visible Survey Control Mark with published coordinates would meet this requirement perfectly.

2. a “reference point feature” in the iD Editor’s OSM Data Layer located at the same coordinates.

GPXRPG is a simple tool to create the required “reference point feature”.
It generates and downloads a GPX track file modelling an Arrow with its tip placed exactly at the published position of the target spot. This track file can then easily be dragged-and-dropped to the iD Editor’s map window to provide that vital OSM reference point feature.

GPXRPG includes a User Guide button which opens a document including an illustrated walk-through of an “armchair mapping” session using a Survey Control Mark and a GPX track file.

You can checkout this program and user guide at www.davidhaycraft.id.au/GPXRPG. Careful - this URL is case-sensitive!