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Updating and Enhancing Maps with Landsat 8

This guest blog post was written by Tom Patterson — one of the creators of the Equal Earth Projection, and Natural Earth Data, (you can read more about Tom here). Learn how he used Geographic Imager for Adobe Photoshop to create two maps from Landsat 8 imagery.

I am a big fan of Landsat 8 satellite images as a resource when making maps. Typically, I use these free images taken every 16 days for verifying and updating other geospatial datasets. I also transfer Landsat textures to shaded relief art in order to better evoke a sense of the physical environment.

The examples that follow demonstrate how I have used Landsat imagery to enhance two maps. The first example is Prince William Sound, Alaska, a map that I am presently working on. The second example is a Landsat mosaic of the Big Island of Hawaii. Both of my examples will give you a general idea on how to integrate Landsat images into your cartographic workflow—using Avenza’s GIS plugins for Adobe Photoshop and Illustrator—with a few technical tips thrown in for good measure. For in-depth information about using Landsat in Photoshop, refer to this tutorial.

Prince William Sound, Alaska

Prince William Sound, in south-central Alaska, is a spectacular place to map. Its sheltered waters are bounded by the lofty Chugach Mountains, indented by deep fjords with tidewater glaciers, and dotted by forest-cloaked islands. The problem I am facing is out-of-date geospatial data because of the rapidly melting of glaciers. For example, the positions of glaciers, lakes, rivers, and coastlines available in the National Hydro Dataset (NHD) have changed considerably since these data were collected between 2008 and 2012. In order to make an accurate map—if only for this year—I have had to re-digitize these vector elements using Landsat images as a reference.

For this task, I used “LandsatLook Images with Geographic Reference” downloaded from the Earth Explorer website. These quasi-natural color images, which come pre-made from bands 7, 5, and 3, clearly depict water bodies, vegetation, bare earth, and glaciers. They were perfect for mapping the changing landscape of Prince William Sound.

Tom Patterson Geographic ImagerNational Hydro Dataset lines overlaid on a LandsatLook image in Adobe Illustrator.
The lines do not match physical features on the more recent satellite image.

For reference, I used images taken on September 29, 2018, about the time when glacier melting ceases before the onset of winter. Images taken later in the fall are hampered by fresh snow cover and deep mountain shadows due to lower sun angles.

Because the LandsatLook images were in the same projection as my map, I could directly place and then register the images in the Adobe Illustrator file with MAPublisher. Had the projections been different, I first would have had to transform the LandsatLook images using the Geographic Imager plugin in Adobe Photoshop. Finally, I moved the LandsatLook images to a bottom layer and dimmed them for editing the lines with Illustrator’s Pencil tool. Using a Wacom tablet and stylus for editing lines greatly improved my drawing speed and accuracy.

If a 30-meter LandsatLook image lacks enough detail, you can increase the apparent resolution to 15 meters by applying panchromatic sharpening. Doing this will involve downloading all data bands that comprise the Landsat scene (a Zipped archive about 1 GB in size). Within this archive is Band 8, a grayscale image showing the same area as the LandsatLook image, but with double the resolution.

Tom Patterson Geographic ImagerComing into focus. A LandsatLook image before (left) and after (right) panchromatic sharpening.
Besides increasing detail, panchromatic sharpening also shifts colors.

Once Band 8 is downloaded, the first step is to enlarge the size of the LandsatLook image by 200 percent in Photoshop (Image/Image Size). Resample it using the Preserve Details (enlargement) option. Next, copy and paste Band 8 on top of the LandsatLook image. Then, in the Layers window, change the blending mode of the Band 8 layer from Normal to Luminosity. Finally, apply Curves adjustments to both layers until the tonal range of the combined image is to your liking. The pan-sharpened LandsatLook image will keep its georeferencing thanks to the Geographic Imager plugin.

Tom Patterson Geographic Imager Landsat8Use the Layers window in Photoshop to apply panchromatic sharpening. 
Selecting Luminosity blending mode for the Band 8 layer is key.

The Big Island, Hawaii

In 2017, I created a Landsat mosaic of the Big Island as a starting point for making two National Park Service maps: Ala Kahakai National Historic Trail and Hawaii Volcanoes National Park. I used the Landsat mosaic as a source for land cover textures—forest cover and historic lava flows (those that formed since 1800)—depicted on these maps. Compared to the Landsat mosaic, the map textures print very lightly in the interest of visual cleanliness.

Tom Patterson Geographic ImagerBig Island Landsat mosaic (left) and the maps of Ala Kahakai National Historic Trail (middle) and Hawaii Volcanoes National Park (right) derived from it. Click here to see a larger version of the Ala Kahakai map (5 MB) and here for the Hawaii Volcanoes map (6.4 MB).

The first step in creating a Landsat mosaic was downloading the appropriate image data. In a perfect world, a mosaic of the Big Island would only require four 185-kilometer-wide Landsat images. However, because of persistent cloudiness on the windward side of the island, ten images were needed to complete a nearly cloud-free mosaic. Using images taken in previous years was a necessity. When selecting older images with fewer clouds, I looked for those taken at about the same time of year to keep the lighting consistent. I then used the Clone Stamp and Spot Healing Brush tools in Photoshop to carefully delete any unavoidable clouds and their shadows from the mosaic. Fortunately, the few clouds that remained were in remote areas far from the main focus of the final maps.

Tom Patterson Geographic ImagerThe Big Island is covered by four overlapping Landsat images.

Tom Patterson Geographic Imager Landsat 8Clouds be gone. The Landsat mosaic before (left) and after (right) editing.

The Landsat mosaic was assembled in Photoshop using Geographic Imager (File/Automate/GI: Mosaic). In the Mosaic window, I selected the Maintain Layers option to ensure that each Landsat image was placed on a separate layer. I then added layer masks to each image layer to piece together the ten images with the goal of avoiding clouds. Although the masks themselves with feathered edges looked like a messy jig-saw puzzle, they combined to produce a seamless Landsat satellite image mosaic.

Tom Patterson Geographic Imager MosaicGeographic Imager’s Mosaic window.

I created the Big Island mosaic in natural color by compositing Bands 4, 3, and 2 as red, green, and blue channels, respectively, in Photoshop. I also brightened the forested areas with LandsatLook mosaic placed on the topmost Photoshop layer and with the layer opacity reduced (in normal blending mode). The natural color procedure is explained in detail here.

With a Landsat mosaic of the Big Island completed, my next task was extracting the forest and lava textures and applying them to the Ala Kahakai and Hawaii Volcanoes maps. But that was an involved procedure that will have to wait for another blog.

One more thing …

Since making the Big Island mosaic in 2017, the Puna district experienced volcanic activity in 2018 that covered a large area in lava and reconfigured the shoreline. Although Puna is the cloudiest area on the Big Island, I was lucky to find a recent cloud-free Landsat image that I then used to update the mosaic. You can download a GeoTIFF of the updated mosaic here (120 MB). It is in the public domain.

Tom Patterson Geographic ImagerPuna District, Hawaii, before (left) and after (right) the volcanic eruptions of 2018.

Cartographer Chronicles: Tom Patterson

The process of making maps can vary greatly depending on the cartographer and the purpose of the map. Tom Patterson, one of the cartographers behind the public domain data set Natural Earth and the popular website Shaded Relief, regards cartography as a creative process. He sees geospatial data as an artist would see paint on their palette. “They are raw materials from which the map is made,” says Patterson. “For me, the map making process starts with an online scavenger hunt for geospatial data, and ends with a visual depiction of the results of that scavenger hunt, a map.”

Patterson recently retired after 26 years with the U.S. National Park Service at the Harpers Ferry Center, located in West Virginia. Harpers Ferry Center is the media hub for the U.S. National Park Service, where most of the maps, exhibits, and publications for public consumption are produced.

Patterson is well-known for making maps with beautiful shaded relief effects, a technique that he has focused on for his entire career. It’s something he has a passion for and is a feature that he believes makes his maps unique. “When making a shaded relief, I go to great pains to portray the natural world in a beautiful and idealized manner, by combining shaded relief with land cover data, drop shadows, gradients and vignettes, with control and restraint,” says Patterson. “I ultimately want to create a shaded relief that readers will find attractive and which will blend harmoniously with the vector elements above.” Patterson prefers light, luminous colours for depicting terrain, and also tell a story. “A map is more than just a combination of points, lines, polygons, type and pixels. To me, a really good map is one that becomes much more than the sum of these parts,” he says. “Maps are an important form of communication, and they should effectively share the ideas of the cartographer to the map reader.”

When making graphically creative maps, you want to use tools that provide you with the most control. With MAPublisher, you can easily access and manipulate geospatial data using Adobe software. “MAPublisher and Geographic Imager bridge the gulf between graphical and GIS worlds.”

Patterson was an early-adopter of MAPublisher, a plug-in for Adobe Illustrator after learning about it in 1996 at the annual North American Cartographic Information Society (NACIS) conference. If you’ve ever used the Natural Earth data, you might be interested to know that most of the vector elements were created with MAPublisher and Adobe Illustrator.

He was also integral in the development of Geographic Imager when during a presentation about manipulating Digital Raster Elevation Model (DEM) data he commented that having a MAPublisher-like software for Adobe Photoshop would be useful. “My suggestion was heard by the President of Avenza, Ted Florence, who was in the audience. He put me in touch with the software development team at Avenza to brainstorm ideas about a GIS plug-in for Adobe Photoshop. Geographic Imager was the eventual result of our discussions.”

Along with his many contributions to the cartographic community, Patterson has held some important positions as the former president and current Executive Director of NACIS. Patterson has created accessible, open source data for global use (Natural Earth), he recently contributed to a new map projection that is taking the cartography and GIS world by storm; Equal Earth. “This equal-area pseudo-cylindrical projection has gained traction rapidly—it seems that cartographers and map users alike have had an unfilled need for world maps depicting countries at true size and presented in a pleasing manner,” he quips.

As an accomplished and respected veteran of the field, we asked that what advice Patterson would give to new cartographers, finding their way? “Seek out advice,” he states. “Map design and production is mostly a solitary task, and any map you create will seem easy-to-understand and logical to you since you are the one who made it. But, your readers may not see it that way,” says Patterson. “The easiest way to avoid these potential ‘failures to communicate’ is by showing drafts of your maps to people that are not family and close friends.”

Another tip that Patterson has for fledgeling cartographers, is to give readers a reason to slow down and read your map. “The trick in today’s media-saturated environment is to design a map that will catch your reader’s eye, ignite their curiosity, and draw them in. Give the most emphasis to the information you want them to remember long after they put down your map.”

Getting the Best Resolution when Importing an Image from a WMS

Using a Web Map Service (WMS) is a great way to easily get up-to-date imagery for your project. An issue you may run into, however, is that a server may not allow you to download images over a certain size (in pixels). The image resolution provided on most servers is usually high enough for most projects but there may be some instances where a higher resolution is needed (e.g. a poster-sized map or a web map that covers a large area).

One possible workaround for this issue is to get several small-area, high-resolution images from a WMS and then mosaic them together to make one large-area, high-resolution image. Here, we will use the City of Toronto Web Map Service to:

  1. Get an image of downtown Toronto
  2. Tile the image to split it into four smaller images
  3. Use the extents of the four tiled images to get four high-resolution images
  4. Mosaic the images to one large high-resolution image

 

Download an Image from the Web Map Service

First we will get an image of downtown Toronto from the City of Toronto WMS. Click the Advanced Import button on the Geographic Imager panel. Select Web Map Service from the Format drop-down and click Browse. Click Load services from Avenza and select City of Toronto WMS from the list.

 

Download an Image from the Web Map Service
(Click for larger version)

 

Select City of Toronto Imagery from the list of layers. Click Select Area then drag a box to zoom in on an area of downtown. Click OK to return to the previous window. There is no need to change the image size because we will use this image to get the extents of a higher resolution image. Leave the other options as default and click OK to load the image, and click OK again on the Advanced Import dialog box. The selected image will now open in Adobe Photoshop.

 

Tile the Image

Next, let’s tile the image to split it into four separate images. Open the Tile dialog box from the Geographic Imager panel. Choose By Number of Tiles as the Tiling Schema and change Horizontal and Vertical to 2. Change the Horizontal and Vertical Overlap to 3 percent. It’s important to have overlap between the images so they will mosaic properly when the data is transformed.

 

Tile the Image
(Click for larger version)

 

Click the Keep Images Open check box to enable it. Choose a name and location to save the tiles. You can save them to a temporary location because they will not be part of the final product. The four image tiles will open in separate tabs.

 

Estimate a Web Map Service’s Maximum Image Size

Open the City of Toronto Imagery WMS again and select an area. In this service, as with many other services, the maximum resolution is not provided. We can, however, use trial and error to find the largest image that the service will allow us to download. A WMS has a maximum allowed width and height set for an image request. The maximum width is usually the same as the maximum height.

Set the resolution of the image by adjusting the width of the image in pixels under Output Options. First, try setting Image Size to a pixel width of 5000. Height will update automatically based on the image’s dimensions. Click OK and you will see an error that says “Parameter ‘width’ contains unacceptable value” (or height if the images higher than it is wide). OK the error to close it.

 

Estimate a Web Map Service’s Maximum Image Size
(Click for larger version)

 

To estimate the maximum width and height allowed by a web service, you can adjust the image size to see when the server returns an error. The maximum width and height for the City of Toronto WMS is about 4000 pixels.

 

Downloading and Mosaicking Large Images

Next we will use the geographic extents of the four tiled images to download four higher resolution images with matching extents then mosaic the images together. Import an image again from the City of Toronto WMS using Advanced Import. Select an area, click Select Area by Another Document’s Extents and choose the first tiled image from the dropdown menu. The Select Area dialog will display an area matching that image’s area. Click OK to return to the previous screen.

 

Downloading large images
(Click for larger version)

 

Enter 3000 as the Image Size. Click OK to add the image to the Advanced Import dialog box. Repeat the above steps for each of the remaining three tiled images.

Creating a mosaic of four images (two by two) makes a single image just under 6000 pixels wide because of the overlap between the tiles (the height will vary depending on the area you selected). This is larger than the maximum size allowed by the WMS. Check the box Mosaic All Files to the Destination Document and select one of the images currently loaded in the dialog window from the drop-down menu. Leave the other options unchecked and select Normal as the Layer Blending Mode. This will merge the four images into a single document.

 

 

Mosaicking large images
(Click for larger version)

 

Avoid Downloading Images Greater than the Maximum Image Resolution

One further consideration when getting imagery from a service is to avoid requesting an image that is higher resolution than the full resolution of the image on the service. In this case, the number of pixels in the image and, therefore, the image size will increase without any increase in the actual resolution of the image.

To see an example of this, get an image from a WMS by zooming in on a small area and downloading images of varying resolution. The pictures below show two images of the same area side by side at different resolutions. The image on the left is 1024 by 870 pixels and the one on the right is 2500 by 2124 pixels but there is no noticeable difference between them. This is because the image exceeds the resolution of the image on the server so the WMS resamples the image to a higher resolution, creating duplicate pixels.

 

Avoid Downloading Images Greater than the Maximum Image Resolution
(Click for larger version)

 

Use Geographic Imager to Import Imagery from ArcGIS Online Directly Into Adobe Photoshop

With the latest release of Geographic Imager 5.2, it’s now possible to easily import images directly from an ArcGIS Online account or an ArcGIS web service. This will allow you to use shared data within your ArcGIS Online organizational account and connect to publicly available map servers from various online sources.

 

ArcGIS Online is a collaborative web GIS that allows you to store and share GIS data using Esri’s secure cloud. Before, you may have had to download raster layers to your local machine and then import them into Adobe Photoshop using Geographic Imager. Now, Geographic Imager has a much-improved workflow to get ArcGIS Online image layers into Adobe Photoshop with full georeferencing.

Currently, the types of datasets allowed are Map Image Layers and Tile Layers. To load a layer, open Advanced Import and select ArcGIS Online from the Format drop-down list. Enter the credentials for your ArcGIS Online account and select an image layer from your user portal.

Images can be resized and transformed on import. To extract a specific area from the image, click Select Area. The interface is the same as the one used for WMS Import.

In addition to using your own organization’s data, you can connect to publicly available data from a wide variety of organizations by connecting to an ArcGIS Web Service. To connect to a web service, use Advanced Import and select ArcGIS Web Service from the Format drop-down menu. Click Browse and enter the URL for the service. This is a great option when searching for data from open data portals created by government agencies.

Validating Georeferencing in Geographic Imager

When georeferencing a map in Geographic Imager, there are two tools which can be used to check spatial accuracy: Validate and Show Image Extents Online. With Validate, click a point on the image and it will show the corresponding location on the web map service so that you can compare the difference between them. Show Image Extents Online will display a rectangle representing the spatial extent of the image on the web map.

The image below shows the Validate tool in action. Selecting the tool and clicking on the road intersection brings up the same intersection in the web map, displaying how accurate the georeferencing may be. It is good practice to test several known points on the image. Choose features that will be easy to identify on the web map such as road intersections, coastlines, buildings, and landmarks.

The Show Image Extents Online tool is shown in the image below. Use this tool to see the full area covered by the image. Note that the rectangle shown on the web map will include the non-map areas of the page (borders, legend, etc).

 

Avenza Systems Fixed and Floating License Solutions: What Are The Differences?

Avenza desktop applications, MAPublisher and Geographic Imager offer two options for the licensing system: Fixed license and Floating license.

The Fixed license option allows only one license per computer. For most users or small companies, this is generally sufficient, even with a few licenses. Since your license is fixed to a specific computer, it can’t be moved freely to another machine. However, Avenza does allow you to move your license occasionally. For example, if you purchased a new computer or when your computer is being fixed and you need to transfer your fixed license to another computer. If your subscription status for MMP (MAPublisher Maintenance Program) or GMP (Geographic Imager Maintenance Program) is up-to-date, then moving your fixed license to another computer (i.e. rehosting a license) can be done without a cost. Complete this form to do so. You will receive a notification email from Avenza when this is completed.

The Floating license option is for users who wants to share a number of licenses on the network. This is a great solution for any size company that has multiple users who share use of MAPublisher or Geographic Imager. You will need to set up a license server for which users will need check out a license from the server before using MAPublisher or Geographic Imager. In general, this option is used when sharing a number of license with colleagues. For example, the license server holds two seats of MAPublisher license. When users on Computer A and Computer B are using MAPublisher, other users can’t check out a license until the borrowed licenses are checked in.

An example environment of a floating license system

Another great advantage of the floating license the ability to borrow a roaming license with their laptop so that they can use MAPublisher and Geographic Imager outside their immediate office. This is a good solution for users who need to use the software on the go and doesn’t have a connection to the floating license server.

For more information about the licensing options for our MAPublisher and Geographic Imager, contact Avenza sales.

If you have any technical questions about setting up a license server or any other licensing issues, contact Avenza Technical Support.

Working With Avenza Floating Licenses Outside of Your Work Network

If you or your organization have a floating license for MAPublisher or Geographic Imager, this blog post is for you. Having a floating license provides you with a lot of flexibility when you want to bring your laptop computer outside your work network and use MAPublisher and Georaphic Imager at home or in the field.

Let’s say you have a laptop computer and you want to work on your mapping project outside your office network. You can do it if your organization has a floating license.

Step 1: Make sure all the software is installed

On your laptop computer, make sure that you have MAPublisher for Adobe Illustrator or Geographic Imager for Adobe Photoshop installed and that there is a valid floating license (for one or each product).

Step 2: Connect your laptop to the network and to the licensing server

If you are not sure how to connect your laptop to the network and to the server, please contact your IT administrator. It is essential that your laptop computer is connected to the license server so that you can obtain a liecnse from it.

Step 3: Follow the steps in the MAPublisher/Geographic Imager license management window

Open the License Management dialog box.

If you’re using MAPublisher, access MAPublisher by going to Help > MAPublisher Licensing > License Management.

If you’re using Geographic Imager, access License Management by going to File > Automate > Geographic Imager: License Management.

Click the Floating button to open the Floating License Setup dialog box.

Make sure that the “Allow roaming licenses” option is selected. Click OK.

Allow roaming licenses

Click the “Use roaming license” option and specify the number of days in the Duration of borrow option. This indicates how long you want to use the license outside of your network.

Specify duration of borrow

Clicking the “Checkout” button will change the status of the license. In this example, we borrowed a license from the license server for two days (December 16, 2015 starting date).

Checkout the license

Now you will be able to use your MAPublisher or Geographic license when your computer is disconnected from your work network.  You might want to test it by closing Adobe Illustrator or Photoshop, disconnect your computer from the network, restart Adobe Illustrator or Photoshop, and see if you can use MAPublisher or Geographic Imager.

Improve Mosaic By Resampling Images in Geographic Imager

The Mosaic function in Geographic Imager merges multiple georeferenced images together to create a single composite georeferenced image. Though the goal of the mosaic is to create a single and seamless composite image, combining images with the Mosaic tool will often result in a slight shift of the imagery due to differences in the original pixel registration grid. This means that even when images are in the same coordinate system with the same spatial resolution, error can still be introduced because of a difference in the pixel alignment. Due to this, mosaicking processes in general tend to produce results that may be very close, but not exact. With this in mind, the results of your mosaic may be improved by resampling your images beforehand to the smallest unit of the resolution.

As an example, let’s say we have an image where the pixel size is 2.00 metres. When plotting the X coordinates of every pixel in this image (using the top left corner of the pixel), the X coordinate value will be incremented by the number/distance of the pixel size. For example, if the X coordinate values were to start at 111.00, then the next pixel would be 113.00, 115.00, 117.00, and so on. It’s important to note that these coordinate values are discrete, which means that the values could not be 113.22 or 115.77 because the origin of the coordinate in this case starts at 111.00 metres.

Now, we have another image that we want to mosaic with the first image. In this instance, the first image will be “Image A” and the second image will be “Image B”. Image B has the same coordinate system as well as the same pixel size as Image A.

Take a look at the X coordinates in Image A and Image B below:

We can see that the X coordinate in the top-left corner is different between these two images, and as previously mentioned, we know that the X coordinate values are discrete. When mosaicking Image B to Image A, the X coordinate cannot be 111.75 or 113.75. The coordinates must be 111.00, 113.00, 115.00, and so on, following the pattern of the pixel grid values in Image A.

This means that Image B will need to be “shifted” or “snapped” to the closest coordinates when the mosaic is performed, see below:

As a result, the X coordinate of Image B will be shifted by 0.75 metres (less than half a pixel). The pixel with X coordinate 111.75 is now placed at 111.00 and the next pixel with X coordinate of 113.75 will now be placed at 113.00, and so on.

With this in mind, the results of your mosaic may be improved by resampling your images to the “smallest unit of the resolution”. The smallest unit of the resolution can be determined from the difference in the coordinates (spatial alignment difference) between the two images.

Looking back at our example, we can see that the smallest unit of the resolution (represented by the blue arrow) in this case is 0.75 metres – this is the value we will use to resample our images.

Once the images have been resampled to 0.75 metres, we may go ahead with our mosaic.

The above example demonstrates the possibility of a pixel shift after a mosaic for two images with a different pixel alignment. It should be noted that this example explains the problem in one-dimension (looking at only the X coordinate) when the image in reality is in two-dimension (looking at both X and Y coordinates). The basic principal of the pixel shift in 2D is the same, but it would include the direction of the shift when mosaicking images. In addition, it’s important to keep in mind that although resampling your images to the smallest unit of the resolution will improve the final mosaic, this is not always an efficient process when mosaicking with more than two images. Another thing to remember is that resampling your images will make your file size much larger. However, in cases where high precision is desired, resampling the images beforehand is a process that should be considered.

Creating a Super Overlay in Google Earth Pro

Our friends in the map library at Brock University in St. Catherines, Ontario have put together a very nice how-to on creating super overlays for Google Earth using Geographic Imager and Adobe Photoshop.

These instructions describe the process of georeferencing a high-resolution image, creating a geotiff file, using Google Earth Pro to make a super overlay and how to provide access to others. The full process is outlined here https://www.brocku.ca/maplibrary/Instruction/Creating_a_super_overlay.pdf

The Brock University Map Library can be contacted at maplib@brocku.ca

3D Terrain Model using Geographic Imager

We created a video to show that it is possible to use geospatial data and the 3D capabilities of Adobe Photoshop. It performs very well with a decent computer and video card.

In this video, a combination of Geographic Imager and Adobe Photoshop functions are used to open a DEM file using a script. The script also transforms a DEM into a 3D model and allows for an overlay of a colour model based on the data or a custom image (e.g. ortho image). Video after the jump.