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Working with Landsat imagery

October 23, 2015

We recently came across this image from NASA’s Earth Observatory, which shows smoke from fires on the island of Sumatra, Indonesia. Given the scale of the phenomena we thought it should be visible in Landsat imagery.

To get the imagery, we used the technique outlined in this post. Landsat 8 takes 16 days to cover the entire earth and adjacent strips of imagery are captured on different days. We looked for images close to the target date that showed some fire activity.

When you import an image into Google Earth Pro using drag-and-drop, it states that ‘the imported image is larger than the maximum size supported by the hardware’. There are options to create a super overlay, scale or crop the image. However, we found that if you scale the image, you can in fact edit the image overlay and set it back to the original unscaled image without problems.

We wanted to display multiple adjacent images, so we needed to get rid of the black background. We first tried editing the images and making the black background transparent. This did work, but it required saving the images as PNG files, because the JPEG format does not support transparency. But PNG files are significantly larger (about 10 times bigger for these files) and thus not suitable if you wish to share them with others. If you are just using Landsat imagery locally, then transparency might be the easiest solution.

So, what we decided to do was to use a graphics editing program (GIMP) to rotate the images and then crop out the black area, keeping them in the JPEG format. We could then use the previously created image overlays as a guide to create new overlays with our rotated and cropped images. To do this easily, in the properties of the image overlay, go to the ‘Location’ tab and click ‘Convert to LatLonQuad’. This makes it easy to line up all the corners with the existing image overlay.

It must be noted that some slight loss of image quality occurs and that image alignment is not perfect, but for our purposes is is good enough.

To see the results in Google Earth download this KMZ file. When looking at the fires and smoke trails, be sure to look at the scale in Google Earth.

Filed Under: Sightseeing Tagged With: image overlay, landsat, landsat 8

Converting a Google Maps screenshot to Google Earth

August 12, 2015

Yesterday we looked at a problem with the Street View layer of Google Earth. We thought it would be interesting to compare the Street View coverage as shown in Google Earth with that shown in Google Maps. However, it is not very easy to compare them side by side due to the different formats.

So, we decided to finally try out something we have long considered doing but not got around to: get a screenshot of a Google Map into Google Earth. We started by capturing a screenshot of the current coverage of Street View in Google Maps at a resolution of 4096×4096 pixels using this file that uses the Google Maps API. Next, we took a screenshot using this screen capture plugin for Chrome.

Google Maps uses the Web Mercator Projection, but Google Earth overlays need to be in the Equirectangular Projection as we mentioned in this post. We found an open source library called GDAL that can convert between different map projections and using suggestions from this page on GIS StackExchange we were able to get our screen shot into the correct projection. We had to use the free image editing program GIMP to convert our initial screen shot to a tiff image, but apart from that there were no difficulties.

All that was left was to create a global overlay from the image and this is the result:

To try it out for yourself, download this KML file.

Also try adjusting the transparency of the image overlay as seen below:

Filed Under: Site News Tagged With: google maps, image overlay, map projections, street view

Using the Google Earth Overlay tool

March 28, 2014

A few months ago we took a look at some of Eric Stitt’s work on genealogy on his blog, and he continues to produce very useful tips. His latest post goes into detail about Overlays, which can be useful to Google Earth users of all levels.

ny township overlay

In researching his past, overlays can be a very valuable tool as he explains here:

I have used overlay for flying routes, shipping lanes, and mostly used for plat maps. I love plat maps, it’s like my little window to the past. You can take a plat map, stretch it over the township your ancestors lived in and then use that to figure out where things from the past laid in today’s land. For instance, how many times have you see a old farm field turn into a subdivision? What I have done is place that plat map over the township and then used placemarkers to mark the Church, School, and Cemetery and then my polygons to mark the farm.

To learn more, check out Eric’s full post or read more of our posts related to overlays.

Filed Under: Google Earth Tips Tagged With: eric stitt, genealogy, image overlay, overlay

Turning a paper map into a 3D image overlay

June 12, 2013

As we mentioned recently with the historic maps from North Carolina, the “image overlay” feature in Google Earth is quite powerful. If you’ve never created one before, Kerry Leith from Stress-driven has written a simple step-by-step walkthrough to help get you started.

It’s really as simple as this:

Kerry goes into a bit more detail in his blog entry, where he walks through the process of taking a useful map from G.J. Hearn and overlays it onto Google Earth.

Good work, Kerry!

Filed Under: Google Earth Tips Tagged With: gj hearn, image overlay, kerry leith, overlay, stress driven

KMZmaps – global overlays for you to use

September 15, 2011

We’ve seen global overlay files before on Google Earth, including items such as the popular blue marble overlay. The folks at KMZmaps.com have created a variety of very high-quality overlays for use in Google Earth. They’re not free, but they’re reasonably priced and quite impressive. Here are few of them:
Natural Globe: A more realistic view of Google Earth, very similar to the blue marble overlay but of considerably higher quality.

natural.jpg

Night Lights: Very similar to the NASA “Earth City Lights” layer.
night.jpg

Colored Edges: There are a variety of Photoshop-edited overlays in here as well; various blurs and effects. Here is one called “colored edges” that is pretty neat.
colored-edges.jpg

They also have a collection of solid color overlays. These overlays are completely solid, effectively hiding the base imagery so that roads, borders and other items are more well-defined. Here is the dark red version of that, with the “Borders and Labels” and “Roads” layers turned on.
dark-red.jpg

Like most maps of this variety, it fades away as you zoom in closer to reveal the base imagery. This allows you to run your favorite overlay all the time, as it will automatically hide itself when you zoom in close enough to look at the details of a specific location. The exception is a special version of the “solid black earth”, which is set to never turn off when you zoom in. They offer both versions, so the choice is up to you.
As I said at the beginning, the big drawback to these files is that they’re not free. They cost roughly $6/each (some vary a bit), with the full collection available for $24.95. However, they also offer a demo map so you can get a feel for how it works. It’s covered with “www.KMZmaps.com” text, but you can get a feel for the quality of the imagery and the way the “auto-hide on zoom” works. You can download the sample KMZ file here. To see more of what they have to offer, visit their site at www.kmzmaps.com.
If you know of other overlays like this, free or paid, leave a comment and let us know.

Filed Under: Sightseeing Tagged With: image overlay, overlay

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