google maps

Google Maps API Maximum Zoom – Part 2: Overview

September 29, 2015

Yesterday we showed you a map of the maximum available zoom level found in Google Maps. If you don’t already have it, download this KML file to view it in Google Earth.

Today we are looking at general features of the data.

Key
First of all, we need to know what the colours mean. The colours represent the various available zoom levels in Google Maps, starting with low resolution at 7 to high resolution at 22. This can be roughly interpreted as follows:

	Low resolution ocean floor
	High resolution ocean floor
	Coastal areas
	Very low resolution satellite imagery (Landsat background imagery)
	Low resolution satellite imagery (CNES/Spot Image background imagery)
	High resolution satellite imagery (DigitalGlobe or CNES Astrium)
	Aerial Imagery (higher resolution than satellite imagery)
	Exceptionally high resolution Aerial Imagery

Google Maps via API
To better understand Google Maps Zoom levels or to explore the data for a given location, you can use this page, which shows a full screen Google Map using the Google Maps API. It behaves a little differently from the standard Google Maps website. The standard Google Maps website restricts how far you can zoom in based on the imagery available, however, it always shows imagery. The above map, obtained via the API, lets you zoom in beyond the maximum prefered amount, and when you do it displays map tiles labelled “Sorry, we have no imagery here”.

Poles
You will notice in our map that there are noticeable bands in the data towards the poles at 60° and 75° latitude, both north and south. We believe these are an artifact of the Google Maps projection, which spreads out the poles, thus magnifying any imagery towards the poles and in consequence requiring less zoom in order to see a given resolution of imagery.

In our data collection we only went 80° north and south. Google Maps itself only goes to 85° north and south as a consequence of its map projection.

Google Earth has noticeable bands in the actual imagery at 80° north across Greenland and about 82.6° south in Antarctica. These are actual changes in the imagery datasets. The absence of high resolution near the poles may be due to the orbits of the imaging satellites or ‘sun angle constraints’.

Oceans
The spider web of tracks across the oceans noticeable in our data reflect the paths of ships equipped with sonar for mapping the ocean floor. The tracks of higher resolution imagery are clearly visible in Google Earth and have in the past been mistaken for Atlantis or an alien base.

In our next post in this series we will be looking in a bit more detail at the various types of imagery found over land.

Google Maps API Maximum Zoom – Part 1: Data collection

September 28, 2015

Ever since we did the posts on historical imagery density we have been looking for a way to map parts of the earth that do not yet have historical imagery. Sadly, the Google Earth plugin does not report historical imagery accurately for such areas.

We recently discovered that the Google Maps API provides a service known as the Maximum Zoom Imagery Service, which allows you to find out what the maximum zoom available in Google Maps is for a given latitude and longitude. The maximum zoom available when in ‘Earth’ mode is dependent on what imagery is available in Google Maps. Since the imagery in Google Maps is almost the same as the default layer in Google Earth, this service can tell us a lot about the imagery in Google Earth.

Today we are just looking at how we gathered the data and prepared it for viewing in Google Earth. In later posts we will look at what is actually in the data and what we can learn about Google Maps and Google Earth imagery.

We queried the Maximum Zoom Imagery Service for every 0.1° from -80° to +80° latitude and every 0.1° of longitude. The result is 5.76 million points of data, which results in multiple KMLs totalling over 1Gb. To display it as a heat map we could have created a KML file with each rectangle as a polygon, but that would probably have crashed Google Earth. So instead we used the technique we used when finding imagery updates and converted the data to an image and displayed that using an image overlay.

If you display each data point as a single pixel, then Google Earth tends to blur the image, so we resized the image to have each data point 4 X 4 pixels. The Maximum Zoom available in Google Maps for the locations we collected varies from 7 to 22, 7 being the lowest resolution imagery and 22 being the highest resolution imagery.

To see it for yourself in Google Earth download this KMl file

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:

Google Maps ‘Earth’ view FOV

March 9, 2015

We recently noticed that if you look at a given place in both Google Earth and Google Maps’ ‘Earth’ view, they look a bit different, with distant objects looking closer in Google Maps than in Google Earth. The main reason for this is that Google Earth by default has a different Field of View from Google Maps.

Last year we showed you how to change the field of view in Google Earth using a tour KML. After some experimentation we reckon that Google Earth by default uses a horizontal field of view (HFOV) of about 60° and Google Maps uses a HFOV of about 35° for its ‘Earth’ view.

So to match up a given location you need to download this KML file, which adjusts Google Earth’s HFOV to 35 degrees. In addition, you may want to try turning on ‘Photorealistic Atmosphere’ in Google Earth’s settings to get the colours to match up a bit better.

Praia Grande, Brazil, with Google Earth’s default settings. Note how the marked building and hill in the distance look further away than in the Google Maps screen shot below.

Praia Grande, Brazil, in Google Maps’ ‘Earth’ view.

Praia Grande, Brazil, in Google Earth with an HFOV of 35° and ‘Photorealistic Atmosphere’.

Google Maps turns 10

February 10, 2015

Google Maps turned 10 on Sunday, February 8, 2015. For a brief history of Google Maps, see Google’s Lat Long blog post, which features a nicely done graphical timeline. Its interesting that they include the purchase of Skybox Imaging. We have high hopes for the future of Skybox, but have not yet seen much impact from it on either Google Maps or Google Earth. Google Earth was first released under that name in 2005, but had previously existed as ‘EarthViewer 3D’ under Keyhole Inc. since 2001. The Lat Long blog’s timeline disagrees with Wikipedia about the exact date of the release of Google Earth.

Google Maps’ Earth View.

Over the years Google Earth and Google Maps have shared and exchanged features to the point where Google Maps now has ‘Earth View’, which is heading towards a Google Earth equivalent in a browser. It is however not yet a Google Earth replacement.