Better simplification possible

MattMatt Global Mapper UserPosts: 176Trusted User
edited June 2009 in Suggestion Box
The simplification feature for polygons results in adjoining polygons that no longer align with each other. The simplified polygon borders often overlap each other or result in open space between the polygons. Not sure if anything can be done to correct for this, but figured can't hurt to bring up. I guess somehow adjoining polygons would need to be transformed so that their vertices match up.

Ultimately the issue that I'm trying to address is the fact that there is not a very good way to import and view complicated polygon files with KML. Raster data has SuperOverlays to deal with this issue, but there isn't any such fix for polygon data, which severely limits the size of polygon data which can be viewed in Google Earth. So I was trying Simplification to get around this, but the resulting polygons don't look very good. Next would be to try and manually create something akin to SuperOverlays with Polygons, where I use Regions/LODs to load more complex polygon regions as Google Earth zooms in. Not sure if there is someway for Global Mapper to do this automatically. Regions/LODs, etc should work the same way for Polygons as they do for Raster so would just need to add simplification levels to the mix. Anyway...I figure this is probably a tall order, but again doesn't hurt to ask.

Matt

Comments

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited May 2009
    Matt,

    For the simplification problem, the real solution is to be able to mark certain vertices of area features as non-removable. Then what you would do is mark the first and last vertices along a shared edge as non-moveable, then the simplification would work the same along the shared edge. Unfortunately there is not any way to do this in Global Mapper.

    I suppose what could be done at some point as v11 will allow simplification in the user interface without exporting is to allow simplifying multiple features at a time and automatically detecting vertices at the end points of shared edges and automatically marking them as non-removable to avoid this issue.

    There is not currently any way to automatically use regions or something like that for the polygon issue. I'm not sure that would work as I think with the current region approach for rasters the lowest resolution data is still always loaded even when zoomed in, you just get the higher res stuff loaded on top to cover it up. This works ok for rasters, but if you used simplified polygons in the lower zoom levels they wouldn't match up and you'd get all sorts of strangeness along the edges.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • MattMatt Global Mapper User Posts: 176Trusted User
    edited May 2009
    For the simplification, it would be impossible to do manually with large dataset. Sounds like you can identify the end points of a shared edge of 2 adjoining polygons. If you can also identify matched vertices between the end points then might be able to do something. I guess ideally, you'd need to identify a shared edge between two adjoining polygons, then simplify that edge and apply the result to both polygons. In other words, instead of simplifying polygons, simplify each shared edge individually.

    I forgot about the issue with regions and polygons. Now that you mention it, I think we looked at that before. Although it seems like it should work since there is option to add Max and Min LODs, which should turn the less detailed layer OFF as it zooms in. I'll play around with it and see if I can figure something out.

    Thanks.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited May 2009
    Matt,

    In theory I can detect the shared endpoints, although it's not something I already have available to me. I'll add this to the todo list to do when simplifying multiple polygons at a time though. So long as some vertices are marked as un-removable, then you'll by definition be just simplifying along the shared segments.

    Where I used to work there was a huge database of polygons that had been manually marked as to where the immovable vertices where just so that simplification and smoothing could take place without causing polygons to come apart.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • MattMatt Global Mapper User Posts: 176Trusted User
    edited June 2009
    Thought about this some more and there might be another solution. GM already has the ability to grid polygon, line, and point data into separate KML files. What if you added the ability for GM to create a simple KML index overlay that would load the grids. See this for example of what I'm talking about.

    http://www.gelib.com/maps/_NL/usgs-topographic-maps.kml

    This dataset contains over 50,000 polygons. But I've broken it down into 1x1 degree blocks. Each 1x1 degree block is initially represented by a simple placemark. Click on the placemark to open up the 1x1 degree block of interest. This way, the user initially only has to download the index and only the polygons of interest are ever downloaded. The same principal could work with polgon, line or point data.

    Not sure if this is the ultimate answer to the problem, but a solution is badly needed and this might be fairly simple for you to implement with GM.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited June 2009
    Matt,

    I think something like that could be possible. I could simply add an option to the vector KML export to generate an index layer in addition to the actual data layers, then when you clicked on the placemark at the center of each index you would get a popup allowing you to actually load the KML file at that index location. I'll try and throw something like that in and point you at a v11 alpha installer with that functionality.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited June 2009
    Matt,

    I have completed adding a new option to generate an index file when doing a KML vector export. This will generate an area and clickable point for each exported file that you can then use to easily open one of the exported tiles. I have placed a v11 beta (really alpha) installer with this support at http://www.globalmapper.com/global_mapper_setup_v1100_beta1.exe for you to try.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • MattMatt Global Mapper User Posts: 176Trusted User
    edited June 2009
    Matt,

    I have completed adding a new option to generate an index file when doing a KML vector export. This will generate an area and clickable point for each exported file that you can then use to easily open one of the exported tiles. I have placed a v11 beta (really alpha) installer with this support at http://www.globalmapper.com/global_mapper_setup_v1100_beta1.exe for you to try.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com

    Thanks Mike, I played around with this a little today and it works like a charm.

    Matt
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