i shared this with Jeff yesterday, he suggested i forwarded it to the
list for broader discussion. it covers some of what i'm dealing with and
thinking about when bringing in various aerial images and maps.
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the issues i'm dealing with are a bit different. these are all imagery
related. images can be actual aerial or satellite imagery, USGS topo
maps, or else maps from other sources. the latter category has its own
issues that are not part of this discussion right now.
basically, i'm georeferencing arbitrary maps and images with a very
primitive sret of tools. a more comprehensive survey of what's out there
might help, but this is what i've got right now:
1) piclayer is a JOSM plugin that lets me align imagery, resulting in an
affine transformation in the 2d plane. it has simple tools for
translation, rotation and scaling. i have a somewhat difficult workflow
that allows me to align the image. with an alignment done, i can then
add nodes/ways/relations to OHM (or OSM). if i want to use the aligned
imagery with my leaflet plugin, well, right now there's a somewhat error
prone process for that.
2) generally i do my geo referencing in JOSM, using piclayer, with OSM
loaded, so i'm using the modern map. this is ok, although twice i've
encountered issues with the underling TIGER data never having been
improved. in both cases, i had to correct the TIGER data to match modern
roads first, once using aerials and once using GPS traces i collected
myself. doesn't scale well.
3) once aligned, the same affine transform generated in JOSM against OSM
works for JOSM against OHM.
4) the available tool for image display in leaflet uses lat/lon for 3
corners of the image (3 so that rotations are handled.) this is a little
distance from the affine transform, and i've not yet worked through the
matrix math to write code to deal with this. the manual process i've
used a couple of times is tedious and error prone, but i wanted to do
proof of concept before i started coding the transform.
so a better method of georeferencing images, perhaps by tying pixels in
the image to nodes in OSM/OHM, and a better method of extracting
alignment parameters to support the leaflet widget, would be of interest
to me.
two image alignment notes:
1) many of the aerials i get off of USGS earth explorer have camera
calibration certificates. it's not out of the question to do an
alignment using a proper 3d camera model instead of the 2d affine
transform. again, i don't have the tools ready to hand for this at this
instant
2) the USGS topo maps, of course, have lat and lon pinned to the 4
corners of the map area. but i lack an alongment tool that would let me
make use of that data.
richard
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Averill Park Networking - GIS & IT Consulting
OpenStreetMap - PostgreSQL - Linux
Java - Web Applications - Search
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