[Flightgear-devel] San Francisco city lake
From: Erik Hofman [EMAIL PROTECTED] http://www.a1.nl/~ehofman/fgfs/gallery/test/san_francisco_natural.jpg http://www.a1.nl/~ehofman/fgfs/gallery/test/san_francisco_fgfs.jpg Someone was complaining about the lake in the middle of the city. I suspect it is the age of the vmap dataset that is to be blamed. There is the long straight dip going towards downtown and also the small lake on the San Andreas fault. In real life, both are fairly deep dips and were, I suspect, tidal and flooded respectively. I suspect that, since the vmap data was collected, the dips were drained and thereby turned into the parkland that you see in the photo. A similar effect is visible in San Diego for the Mission Bay area; any long term local who sees our scenery immediately knows when the vmap0 data was recorded; only recent arrivals refer to it as 'wrong'. Therefore, I suggest we leave the lake as-is (unless someone who has lived in the area for a couple of decades has better historical data). I don't think we can have a simple rule to determine which lakes and swamps will have been drained or paved over during the last 20-50 years. ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] San Francisco city lake
Alex Perry writes: From: Erik Hofman [EMAIL PROTECTED] http://www.a1.nl/~ehofman/fgfs/gallery/test/san_francisco_natural.jpg http://www.a1.nl/~ehofman/fgfs/gallery/test/san_francisco_fgfs.jpg Someone was complaining about the lake in the middle of the city. I suspect it is the age of the vmap dataset that is to be blamed. There is the long straight dip going towards downtown and also the small lake on the San Andreas fault. In real life, both are fairly deep dips and were, I suspect, tidal and flooded respectively. I suspect that, since the vmap data was collected, the dips were drained and thereby turned into the parkland that you see in the photo. A similar effect is visible in San Diego for the Mission Bay area; any long term local who sees our scenery immediately knows when the vmap0 data was recorded; only recent arrivals refer to it as 'wrong'. Therefore, I suggest we leave the lake as-is (unless someone who has lived in the area for a couple of decades has better historical data). I don't think we can have a simple rule to determine which lakes and swamps will have been drained or paved over during the last 20-50 years. After all the scenery crunching is finished, this area comes out as type default. In other words, the vmap0 data has no opinion about what the coverage is there, but some place it is recorded as land so it is left as default. The real issue here is what texture should we choose for default areas for which vmap0 has no coverage opinion? I would argue that water or sand is not the best choice. It may work well for a few specific instances, but then you are going to get lake or water in a ***lot*** of places where it shouldn't be. Instead we need to use an existing ground cover texture or come up with something that is slightly more generic and nondescript ... i.e. it could be grassy, or maybe it's trees, we can't quite tell; and it's not too green, but not too dry, not too rocky, not too grassy, not too urban, etc. etc. Regards, Curt. -- Curtis Olson HumanFIRST Program FlightGear Project Twin Citiescurt 'at' me.umn.edu curt 'at' flightgear.org Minnesota http://www.menet.umn.edu/~curt http://www.flightgear.org ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] San Francisco city lake
On Monday, September 8, 2003, at 04:07 pm, Alex Perry wrote: I suspect that, since the vmap data was collected, the dips were drained and thereby turned into the parkland that you see in the photo. The problem is, that 'lake' is the Golden Gate Park. Having it be anything other than green parkland would be as wrong as having Central Park show up as water or sand in NY city! Note I'm not arguing that the park isn't low enough (or sandy enough) at the western end to have been tidal flats in the past, but it's been a park for a long time, and the land rises up (and gets less sandy) less than a quarter of the way east. The impression I have is that no matter what texture is picked for 'default' landcover, it's going to be massively, obviously wrong much of the time. James ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] San Francisco city lake
James Turner [EMAIL PROTECTED] wrote: The impression I have is that no matter what texture is picked for 'default' landcover, it's going to be massively, obviously wrong much of the time. This leads to the assumption that there is need for another source of landcover data. The SRTM mision not only collected data on earth elevation but also land coverage. Does anyone know if this data is acessible ? Martin. -- Unix _IS_ user friendly - it's just selective about who its friends are ! -- ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] San Francisco city lake
Curtis L. Olson writes: The real issue here is what texture should we choose for default areas for which vmap0 has no coverage opinion? It would be nice if we could do some kind of weighted average of the surrounding areas, excluding water. At least we'd be less likely to get something out of place (like an evergreen forest in the middle of the desert). We could also default to the 1 arcsec landcover raster. All the best, David ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
RE: [Flightgear-devel] San Francisco city lake
David Megginson writes: Curtis L. Olson writes: The real issue here is what texture should we choose for default areas for which vmap0 has no coverage opinion? It would be nice if we could do some kind of weighted average of the surrounding areas, excluding water. At least we'd be less likely to get something out of place (like an evergreen forest in the middle of the desert). We could also default to the 1 arcsec landcover raster. I would look up the center of the area in question in the global landcover This should be very quick Also for water area delineation the Hydrographic database in the message I forwarded to the terragear list should be quite good as it has had *lots* of corrections applied Cheers Norman ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
RE: [Flightgear-devel] San Francisco city lake
Julian Foad writes: Norman Vine wrote: Also for water area delineation the Hydrographic database in the message I forwarded to the terragear list should be quite good as it has had *lots* of corrections applied The fact that something has had lots of corrections applied does not necessarily mean it is quite good ... it could also mean it is quite bad. :-) yup, I guess we all should just use Ptolemy's map. Norman ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] San Francisco city lake
On Monday 08 Sep 2003 16:15, Curtis L. Olson wrote: Alex Perry writes: From: Erik Hofman [EMAIL PROTECTED] http://www.a1.nl/~ehofman/fgfs/gallery/test/san_francisco_natural.jpg http://www.a1.nl/~ehofman/fgfs/gallery/test/san_francisco_fgfs.jpg Someone was complaining about the lake in the middle of the city. I suspect it is the age of the vmap dataset that is to be blamed. There is the long straight dip going towards downtown and also the small lake on the San Andreas fault. In real life, both are fairly deep dips and were, I suspect, tidal and flooded respectively. I suspect that, since the vmap data was collected, the dips were drained and thereby turned into the parkland that you see in the photo. A similar effect is visible in San Diego for the Mission Bay area; any long term local who sees our scenery immediately knows when the vmap0 data was recorded; only recent arrivals refer to it as 'wrong'. Therefore, I suggest we leave the lake as-is (unless someone who has lived in the area for a couple of decades has better historical data). I don't think we can have a simple rule to determine which lakes and swamps will have been drained or paved over during the last 20-50 years. After all the scenery crunching is finished, this area comes out as type default. In other words, the vmap0 data has no opinion about what the coverage is there, but some place it is recorded as land so it is left as default. The real issue here is what texture should we choose for default areas for which vmap0 has no coverage opinion? I would argue that water or sand is not the best choice. It may work well for a few specific instances, but then you are going to get lake or water in a ***lot*** of places where it shouldn't be. Instead we need to use an existing ground cover texture or come up with something that is slightly more generic and nondescript ... i.e. it could be grassy, or maybe it's trees, we can't quite tell; and it's not too green, but not too dry, not too rocky, not too grassy, not too urban, etc. etc. Regards, Curt. -- Curtis Olson HumanFIRST Program FlightGear Project Twin Citiescurt 'at' me.umn.edu curt 'at' flightgear.org Minnesota http://www.menet.umn.edu/~curt http://www.flightgear.org Could you not replace all 'default' coverage with one of the coverages bounding the area of default cover? LeeE ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] San Francisco city lake
Could you not replace all 'default' coverage with one of the coverages bounding the area of default cover? I thought about that too, but I think it will destroy some detail. There's a small lake in the west of Amsterdam that turns up as default coverage. I use it when I fly around the place, just to see where I am. Though it's not blue (but looks more like a park) I know what it is and thus is helpful. If it was replaced by the coverages of the bounding area, it would turn out to be urban and the whole lake would be lost. I can imagine similar situations occur in other places. --Ivo ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
