My Google Map Blog

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.

The post Working with Landsat imagery appeared first on Google Earth Blog.

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:

The post Converting a Google Maps screenshot to Google Earth appeared first on Google Earth Blog.

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.

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.

The post Using the Google Earth Overlay tool appeared first on Google Earth Blog.

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!

The post Turning a paper map into a 3D image overlay appeared first on Google Earth Blog.