| 03:09:07 | sigq: | osgeofeed: Changeset [2923]: avoid repeats in the package hog list <http://trac.osgeo.org/osgeo/changeset/2923> |
| 03:09:29 | CIA-14: | osgeo: hamish * r2923 /livedvd/gisvm/trunk/bin/main.sh: avoid repeats in the package hog list |
| 03:43:21 | sigq: | osgeofeed: Changeset [2924]: git package moved to gnuit <http://trac.osgeo.org/osgeo/changeset/2924> |
| 03:43:37 | CIA-14: | osgeo: hamish * r2924 /livedvd/gisvm/trunk/bin/setup.sh: git package moved to gnuit |
| 04:18:10 | CIA-14: | osgeo: hamish * r2925 /livedvd/gisvm/trunk/bin/install_gpsdrive.sh: updates for karmic pkg versions |
| 04:18:12 | sigq: | osgeofeed: Changeset [2925]: updates for karmic pkg versions <http://trac.osgeo.org/osgeo/changeset/2925> |
| 07:34:06 | lambda: | hi, currently I am testing OSGeo4W on MS Windows Server 2008 ( 64bit ) and I have significant problem with MSys, when I start MSys it's open 129times and then fails, has anyone similar experience here? |
| 08:15:05 | sigq: | osgeofeed: Changeset [2926]: call4workshop and workshop/tutorial page added <http://trac.osgeo.org/osgeo/changeset/2926> |
| 08:15:33 | CIA-14: | osgeo: lbecchi * r2926 /foss4g/2010/website/ ( index.php navigation.php ): call4workshop and workshop/tutorial page added |
| 08:16:20 | CIA-14: | osgeo: lbecchi * r2927 /foss4g/2010/website/workshop.php: workshop/tutorial page now added |
| 08:16:26 | sigq: | osgeofeed: Changeset [2927]: workshop/tutorial page now added <http://trac.osgeo.org/osgeo/changeset/2927> |
| 14:27:35 | dandy: | question from the inexperienced for the experienced, are there any projections with different datums but using the same elipsoid? |
| 14:35:32 | jgarnett: | thinking; not sure I am that smart in the morning |
| 14:36:41 | jgarnett: | I am pretty sure there are ... but am drawing a blank at how to check. |
| 14:39:29 | dandy: | another question I have |
| 14:39:35 | dandy: | why does MultiPolygon exist? |
| 14:40:55 | dandy: | as far as I can see the only difference is that MultiPolygon allows for multiple external fill rings |
| 14:41:09 | dandy: | but I don't see why Polygon is restricted from that |
| 14:41:16 | dandy: | is there some historical or legacy reason for this? |
| 14:42:25 | jgarnett: | um a polygon is a single thing; ie from geometry class |
| 14:43:08 | jgarnett: | when they start doing GIS to describe real world things |
| 14:43:21 | jgarnett: | they run into the situtation where the same "idea" has several physical representations ( ie polygons ) |
| 14:43:21 | dandy: | Polygon allows for multiple rings |
| 14:43:31 | jgarnett: | they would like to treat the group as a single name; and thus made up "multi polygon" for the purpose |
| 14:43:32 | jgarnett: | an example would be the base supports of a large bridge |
| 14:43:46 | jgarnett: | they are all "the bridge" but each support takes up some area on the ground that roads need to go around |
| 14:46:26 | jgarnett: | thought it was a "bound area" of some sort |
| 14:46:26 | jgarnett: | ie I don't think they allow for multiple rings |
| 14:46:34 | jgarnett: | it could be that the kind of polygon used in gis is restricted as all get out; ie "simple" "not self intersecting" and so on ... |
| 14:46:34 | dandy: | yeah I get the nomenclature thing but in GIS terms, Polygon and MultiPolygon differ only in the number of a certain type of ring. |
| 14:46:34 | dandy: | Polygon does allow for multiple rings |
| 14:46:35 | dandy: | maybe |
| 14:46:35 | jgarnett: | so I expect this is an accident of history and math; and multi polygon is the work around... |
| 14:46:36 | dandy: | do MultiPolygons allow the Polygons within them to intersect? |
| 14:47:16 | dandy: | yeah it seems like it |
| 14:50:49 | dandy: | i think I am going to ditch the concept of multipolygon internally in stuff I write and instead write something to help interoperate with it |
| 14:51:08 | jgarnett: | hrm; you would be a bit on your own there |
| 14:51:08 | jgarnett: | JTS, SDO_GEOMETRY and so on all take pains to seperate out the two cases |
| 14:51:08 | dandy: | ? |
| 14:51:08 | jgarnett: | for polygon having multiple rings; usually it is defined as a single outer ring; and many internal ones |
| 14:51:09 | jgarnett: | ( some systems even force the rings to be counter clockwise for oter or clockwise for interior ) |
| 14:51:09 | jgarnett: | JTS Topology Suite; ported to C++ for GEOS etc... |
| 14:51:09 | jgarnett: | SDO_GEOMETRY is the oracle spatial representation of geometry |
| 14:51:09 | pramsey: | MulitiPolygons do not allow ring interactions. |
| 14:51:09 | jgarnett: | when you say polygon does allow for multiple rings; what software are you refering to? |
| 14:51:09 | pramsey: | However, dispensing with MultiPolygon is not the asnwer. |
| 14:51:09 | dandy: | right |
| 14:51:09 | dandy: | so internally for my algorithms I would have a polygon that supports multiple outter rings |
| 14:51:09 | dandy: | but when I need to interoperate I can quickly convert that polygon or collection of polygons into something more conformant |
| 14:51:51 | pramsey: | Dispensing with Polygon is. Since a Polygon can be easily represented as a one-part multipolygon. |
| 14:51:53 | jgarnett: | dandy perhaps you are confusing what can be done with what is valid? |
| 14:52:06 | pramsey: | ( in fact, that's how shape files model things. all the objects are assumed to be multipart ) |
| 14:52:28 | dandy: | well I suppose I am looking at it wrong, I am instead going to use a multipolygon and then later have to downconvert it to polygons |
| 14:52:41 | dandy: | polygon winding is not an issue as long as it is consistent and can be easily corrected |
| 14:54:35 | : | * pramsey thinks being explicit about what's an exterior ring and what's an interior one is more robust. |
| 14:54:35 | pramsey: | that relying on any kind of vertex ordering rule |
| 14:54:35 | dandy: | pramsey, I think that is how I should look at it, thanks |
| 14:55:01 | dandy: | jgarnett, examples are shapefile, OGC, etc... |
| 14:55:11 | dandy: | yeah I have a optional flag for hole or fill |
| 14:55:15 | dandy: | but also allow for winding |
| 14:55:26 | dandy: | I totally agree with the explicit flag |
| 14:55:33 | dandy: | especially when dealing with multiple data sources |
| 14:55:41 | dandy: | shp,sde,ogc, etc.. |
| 14:56:04 | dandy: | then bringing in data from non GIS sources tends to be CCW while SHP is CW if I remember correctly |
| 14:56:05 | jgarnett: | cool |
| 14:57:11 | pramsey: | WRT your projection question: yes |
| 14:57:36 | dandy: | thanks |
| 14:57:41 | pramsey: | lots of projections that are the same but for datum and lots of modern projections that differ in datum |
| 14:59:13 | pramsey: | eg EPSG: 26910, EPSG:26710 |
| 14:59:42 | dandy: | perfect, love examples |
| 15:01:41 | dandy: | thanks a bunch |
| 19:04:07 | FrankW: | hobu, crschmidt: is something up with spatialreference.org? I don't seem to be able to reach it. |
| 19:38:38 | crschmidt: | Working on it. |
| 19:43:20 | crschmidt: | FrankW: fixed. |
| 19:44:01 | FrankW: | thanks |
| 19:44:11 | FrankW: | I must confess my need has passed. |
| 19:44:38 | crschmidt: | Understood. |
| 19:44:49 | crschmidt: | I apologize for not having instant reaction at 11:45 at night : ) |
| 19:44:53 | crschmidt: | ( or 11:15 ) |
| 19:45:06 | FrankW: | no problem, of course. |
| 19:45:18 | FrankW: | I just consulted the libgeotiff epsg csv files. |
| 19:45:30 | FrankW: | But some folks might not have mastered that fallback |
| 19:46:05 | : | * crschmidt nods. |