Comments on: Animating Sea Level Rise In San Francisco With Vector Overlays In Google Earth In One Word: Don't http://freegeographytools.com/2007/animating-sea-level-rise-in-san-francisco-with-vector-overlays-in-google-earth-in-one-word-dont Exploring the world of free tools for GIS, GPS, Google Earth, neogeography, and more. Wed, 18 Nov 2009 03:05:04 -0700 http://wordpress.org/?v=2.8.6 hourly 1 By: Leszek Pawlowicz http://freegeographytools.com/2007/animating-sea-level-rise-in-san-francisco-with-vector-overlays-in-google-earth-in-one-word-dont/comment-page-1#comment-499 Leszek Pawlowicz Fri, 07 Dec 2007 19:35:28 +0000 http://freegeographytools.com/?p=202#comment-499 Thanks for your comment. To create the flooding simulation, I used the freeware GIS MicroDEM to flood an area, then converted it into a KML overlay, either raster or vector. MicroDEM does a true basin flood of a DEM, so it doesn't have the issues with approaches like yours, e.g. the earth's curvature or flooding areas that would be kept from flooding in real life by the topography (like Death Valley). The downside is that it takes a lot more time and effort to create, and as a raster overlay it uses more memory (unless I convert it to a tiled overlay). The limited terrain resolution of Google Earth used to limit the accuracy of a generic "rising vector overlay" flooding approach, which is why I came up with my approach. But since I created my simulations, Google Earth has improved the terrain resolution in the US from 30 meters to 10 meters, which significantly improves the results you get from your approach, or similar ones like that of BZoltan's worldwide sea level flooding KMZ file: http://bbs.keyhole.com/ubb/showthreaded.php/Cat/0/Number/847094 With the old 30-meter resolution, BZoltan's simulation was fairly inaccurate; with the 10-meter resolution, it resembles my results pretty closely. If you don't have to worry about terrain effects on flooding, it's a lot easier to use. I don't know what the terrain resolution for Canada is in Google Earth, but I suspect it's not at the 10-meter level. In any case, I think most people in Vancouver will be safe unless the Greenland and Antarctic ice sheets melt significantly. If they melted completely, the maximum rise would be about 65 meters. Thanks for your comment. To create the flooding simulation, I used the freeware GIS MicroDEM to flood an area, then converted it into a KML overlay, either raster or vector. MicroDEM does a true basin flood of a DEM, so it doesn’t have the issues with approaches like yours, e.g. the earth’s curvature or flooding areas that would be kept from flooding in real life by the topography (like Death Valley). The downside is that it takes a lot more time and effort to create, and as a raster overlay it uses more memory (unless I convert it to a tiled overlay).

The limited terrain resolution of Google Earth used to limit the accuracy of a generic “rising vector overlay” flooding approach, which is why I came up with my approach. But since I created my simulations, Google Earth has improved the terrain resolution in the US from 30 meters to 10 meters, which significantly improves the results you get from your approach, or similar ones like that of BZoltan’s worldwide sea level flooding KMZ file:

http://bbs.keyhole.com/ubb/showthreaded.php/Cat/0/Number/847094

With the old 30-meter resolution, BZoltan’s simulation was fairly inaccurate; with the 10-meter resolution, it resembles my results pretty closely. If you don’t have to worry about terrain effects on flooding, it’s a lot easier to use.

I don’t know what the terrain resolution for Canada is in
Google Earth, but I suspect it’s not at the 10-meter level. In any case, I think most people in Vancouver will be safe unless the Greenland and Antarctic ice sheets melt significantly. If they melted completely, the maximum rise would be about 65 meters.

]]> By: Mark Ireland http://freegeographytools.com/2007/animating-sea-level-rise-in-san-francisco-with-vector-overlays-in-google-earth-in-one-word-dont/comment-page-1#comment-498 Mark Ireland Tue, 27 Nov 2007 19:34:40 +0000 http://freegeographytools.com/?p=202#comment-498 We (Safe Software) did a very similar demonstration at a recent GIS Day event. We used our software (FME) to convert some data to KML and duplicate it in a way that created a time-span and simulated flooding. I'd be interested to know what your KML technique was - we simply created a large vector polygon that spanned the entire area, then raised it up 1m per time frame. It's what we'd use to create a 3d building, but in this case it produced the flooding effect we wanted. We had a similar problem where it didn't flood when we thought it should, and we figured that it was caused by curvature of the earth using too large a polygon (what is 1m above sea level at the edge of the polygon was still underneath sea level at the centre where the curvature is highest), so we tiled it and it reduced the effect at the cost of a little performance. You can find what we did on fmepedia.com (see workspace of the week for some screenshots) - or you can download the kml inside a zip file at http://www.fmepedia.com/attachments//Main_Page/VancouverFloodDemo.zip NB: To give a greater effect we made the sea-level raise 40m and pretended it was caused by a tsunami. I guess in reality that would be a different type of flooding, but it was the method more than the reality that we were concerned with. Anyway - a cool article here and good to see great minds thinking alike(!) and using GE for the same demo. I shall have to investigate how you did the raster overlay to pick up some useful tips. Mark Mark Ireland, Senior Product Specialist Safe Software Inc. Surrey, BC, CANADA support@safe.com http://www.safe.com Solutions for Spatial Data Translation, Distribution and Access We (Safe Software) did a very similar demonstration at a recent GIS Day event.
We used our software (FME) to convert some data to KML and duplicate it in a way that created a time-span and simulated flooding.

I’d be interested to know what your KML technique was – we simply created a large vector polygon that spanned the entire area, then raised it up 1m per time frame. It’s what we’d use to create a 3d building, but in this case it produced the flooding effect we wanted.

We had a similar problem where it didn’t flood when we thought it should, and we figured that it was caused by curvature of the earth using too large a polygon (what is 1m above sea level at the edge of the polygon was still underneath sea level at the centre where the curvature is highest), so we tiled it and it reduced the effect at the cost of a little performance.

You can find what we did on fmepedia.com (see workspace of the week for some screenshots) – or you can download the kml inside a zip file at http://www.fmepedia.com/attachments//Main_Page/VancouverFloodDemo.zip

NB: To give a greater effect we made the sea-level raise 40m and pretended it was caused by a tsunami. I guess in reality that would be a different type of flooding, but it was the method more than the reality that we were concerned with.

Anyway – a cool article here and good to see great minds thinking alike(!) and using GE for the same demo. I shall have to investigate how you did the raster overlay to pick up some useful tips.

Mark

Mark Ireland, Senior Product Specialist
Safe Software Inc. Surrey, BC, CANADA
support@safe.com http://www.safe.com
Solutions for Spatial Data Translation, Distribution and Access

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