High Resolution Image Overlays

[automan25]

It appears that Google Earth downsamples high resolution imagery that I try to import as an image overlay. If I recall from something I read...the limit is 1024 px square. I could create a Photoshop action to break-up the image into smaller tiles, but then piecing them back together in GE by hand would be a real pain. Does anyone know of a program that automates this process?

[Forkboy2]

Google Earth 4 beta has a new feature called regions that lets you overlay high resolution imagery. I've been doing some experimenting with the Super Overlays, as they seem to be called. The following KML has 10 high resolution topo map overlays that are each split into about 350 smaller image tiles, each with a resolution of about 256x256.

http://www.fox-fam.com/gefiles/topos3/60minTopos.kml

I'm not totally happy with the results as the image tiles load very slowly and I don't think it's an issue with my server. I may be able to tweak some of the KML settings to get better results, but I think Google Earth is just too slow in processing all the KML files. It works much better if there is just one overlay loaded at a time. Maybe the final version of GE4 will be better.

I've come up with a semi-automatic process to create the image tiles and KML files. It basically involves Global Mapper, an Excel spreadsheet, MS Word's Mail Merge feature, Irfanview and a couple UltraEdit macros. Sounds complicated, but each overlay only takes about 10-15 minutes to process, which isn't bad considering all the KML code and images that have to be created. An it's limited to breaking a single overaly up into either a 16x16 grid of tiles or a 32x32 grid of tiles. The 32x32 grid is almost unuseable though because GE is so slow in processing the tiles.

More info on my progress here:
http://www.topomaps.fox-fam.com/index.php

Matt

[automan25]

That sounds like just what I'm looking for. I was hoping you're webstie would have a set of instructions on how to create super overlays, but I didn't find any. Do you plan on posting some instruction in the (near) future?

[macnetz]

hi,

all needed instructions you can find in the KML 2.1 tutorial. But AFAIK at the moment there is no script available to automate the tremendous task.

Regards - Anton

[Forkboy2]

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That sounds like just what I'm looking for. I was hoping you're webstie would have a set of instructions on how to create super overlays, but I didn't find any. Do you plan on posting some instruction in the (near) future?

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I hadn't posted specific instructions because the process is a bit complicated and there are specific programs (most of which are not free) that are required for the process that I'm using. Also, my process is geared toward square maps that are less than about 7,000x7,000 pixels in size.

If you have Global Mapper, Excel, Word, Irfanview and UltraEdit 12, I'd be happy to provide you with instructions and the templates

Basically, it involves these steps.

KML generation:

1) Enter lat/lon of map corners into and excel spreadsheet, which then generates all the corner coordinates needed for every tile and KML file.

2) Use Words Mail Merge feature to import all the data from Excel into KML code.

3) Export the KML code from Word into a single huge TXT file

4) Use UltraEdit macro to split the TXT file into hundreds of smaller KML files.

Tile generation:

1) Use Global Mapper to generate the tiles.

2) Use Irfanview to resize all the tiles to 256x256 and 96 color compressed PNG.

That's it Sounds simple now, but took me a few weeks to figure it all out and get it working correctly.

I suspect that eventually there will be a more user friendly way to do this.

There are a couple of other ways to generate tiles for free. There is a program called dstile (search WorldWind forums) but not sure of the naming convention dstile uses. Global mapper simply starts at the top left corner and names the tiles in sequential order until it reaches the lower right corner.

Matt

[macnetz]

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Basically, it involves these steps.

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Hi Matt,

you described the "easy way"
. . . if the map tiles are in the correct projection and the correct map datum and the coordinates are lat/long.

It's far more complicated if every tile has to be rotated and if you cannot use the coordinates of the corners to generate the lat/long box.

Regards - Anton

[Forkboy2]

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Yes, you will need to pre-process your images to get them in correct format. But you would probably need to do that no matter what method you choose.

By the way, Global Mapper (www.globalmapper.com) is probably the best program out there for doing that kind of map translation. It makes it very easy to georeference an image and once it's georeferenced you can change it to any projection/datum you wish very easily.

Matt

[macnetz]

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Yes, you will need to pre-process your images to get them in correct format. But you would probably need to do that no matter what method you choose.

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Hi Matt,

I prefer the different approach . . .
. . . not to reproject the original image, but use some tools to get the correct lat/long and rotation. In Europe many maps are drawn in Transverse Mercator Projection and the coordinates are written in National Grids or UTM. You can find some examples on my webpage.
- by hand (with Regions): http://mac-im-netz.de/dateien/keyhole/RAM-21.kml
- with help from TTQV (without Regions): http://www.graja.es/docs/OE-13-15.kmz (2.1 MB)

Regards - Anton

[Forkboy2]

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As long as its just a matter of rotating and converting lat/long that should work. But if you have a projection without parallel lat/long lines you're going to have problems.

Like most things in life, there are more than one way to peform a task

Matt

[BrianT]

Inspired by Jason Birch's work here , we finally got around to setting up a MapServer instance that serves up large images via WMS. The key is that the script does all the cutting "on-the-fly" so you don't have to mess with it. The performance is acceptable, especially in a local environment.

In short, if you're interested in streaming more than a couple of images, this might be the way to go.

BT