I know we're not that big on commercial software, but the esri smooth/simplify tools will fix that first problem very quickly. You really cannot do a spline interpolation though, because that requires true curves which are not supported by the OSM format (nor PostGIS). You could do a polyline approximation of a spline interpolation, but after you simplify, interpolation, then approximate off a dataset that is already a generalization, how far away are you from the real world data? (To make this worse, the California shapefiles are polygon conversions of 5m raster data, hence the points every 5m. The nice part is that you can be reasonable certain that 5/2 * sqrt(2) meters is the correct allowable deviation for a smooth/simplify. For the last problem, if the ways are overlaying each other rather than overlapping, a conversion to a topological data format will eliminate that problem quickly. If the ways are truly crossing, than an esri topology can go a long ways towards fixing those. Instead though, I would suggest a direct conversion to raster (or get ahold of the original raster data) and then a smoothed raster to polygon conversion to fix that. Brett Lord-Castillo Information Systems Designer/GIS Programmer St. Louis County Police Office of Emergency Management 14847 Ladue Bluffs Crossing Drive Chesterfield, MO 63017 Office: 314-628-5400 Fax: 314-628-5508 Direct: 314-628-5407
-----Original Message----- Date: Tue, 29 Dec 2009 23:43:45 -0800 From: <[email protected]> Subject: [Talk-us] California land cover import To: <[email protected]> Message-ID: <000301ca8923$d29dd460$77d97d...@com> Content-Type: text/plain; charset="us-ascii" The state of California has some good landcover shapefiles on the Department of Forestry and Fire Protection site. They are sorted by county. The smallest are under a meg while the largest - Fresno - is more than 400 megs. The average size is around 30 to 40 megs. These would be a great addition to OSM since they contain valuable metadata. Once the areas have been added, the state will take on a similar look to states like Georgia and Massachusetts that have had statewide imports done. Another good example of what California can be is the Corine Land Cover (WikiProject Corine Land Cover). There are several challenges with the data. Here are a couple. * It is a huge dataset and will need some optimization. The straight lines have points every five meters, creating jagged edges that aren't visually attractive. Josm has a plugin but that's probably not the best way. A spline interpolation would really improve it dramatically. It will increase data size, but it's worth it. Maybe there is a batch mode program available to do that. Mapshaper has a tool to optimize a shapefile by reducing the details in the file. It may not be working though. Here is a rough idea of what the areas look like without being simplified. * Only vegetation data should be used. The urban/residential/water/unknown should be skipped since the quality isn't good enough for this purpose and would just create tons of conflicts with existing data. Also there is/will be better data available. * We can use some filters to split the shapefiles into different features. This is also great to prepare the OSM files for each type instead having it mixed all together. * All these polygons have overlapping ways. This should be avoided because it creates tones of duplicate nodes/ways. Each polygon should be split in single ways and the area defined with a relation. According to the description, mapshaper will do that to. There may be a way to do this with postgis or through a Perl script. Validator will just merge duplicate nodes, but can't fix duplicate lines. This is really a tricky thing that many other updates lack. Efficiency should be considered here. Also editing is easier then. This data shouldn't need much editing after import. Please feel free to add your comments and suggestions on the California Land Cover wiki page. This is also being posted to the imports list. -------------- next part -------------- An HTML attachment was scrubbed... URL: http://lists.openstreetmap.org/pipermail/talk-us/attachments/20091229/3d9481ae/attachment-0001.htm ------------------------------ _______________________________________________ Talk-us mailing list [email protected] http://lists.openstreetmap.org/listinfo/talk-us End of Talk-us Digest, Vol 25, Issue 47 *************************************** _______________________________________________ Talk-us mailing list [email protected] http://lists.openstreetmap.org/listinfo/talk-us
