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Archive for the 'MicroDEM' Category Page 2 of 5

Goofing Around With Pan-sharpening

Orbiting satellites often have two types of digital imaging sensors:

– Multispectral, i.e. different sensors for different colors (including IR), or different filters in front of the same sensor. Each individual band can be shown as a black-and-white image; multiple bands can each be assigned a color, and combined to form an RGB color image.

– Panchromatic, “meaning all the colors”, a single broad-spectrum sensor. This are usually displayed as a monochromatic image (i.e. black-and-white).

The panchromatic sensors usually have a higher spatial resolution than the multispectral. For example, on the Landsat 7 spacecraft, the 6 multispectral bands have a spatial resolution of roughly 30 meters (a seventh has 60 meters), while the panchromatic sensor has a resolution of about 15 meters. Here’s an example of an image created from three of the Landsat multispectral bands (data from the Global Land Cover Facility):

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Embedding And Extracting Worldfiles With MicroDEM

As described in a previous post, the TatukGIS Viewer has the ability to open image files along with their associated worldfiles, and then convert the image to a GeoTiff with the worldfile georeferencing data embedded it. It can also open a georeferenced image file like a GeoTiff or MRSid, and then save it in JPG, PNG, BMP or TIF formats while creating an associated worldfile. The two biggest drawbacks are that it stamps every exported image at the bottom with the message “Exported with the TatukGIS Viewer” in yellow-accented letters, and it can’t embed coordinate system and datum data in the GeoTiff (e.g. UTM, WGS84). MicroDEM can’t do everything that the TatukGIS viewer can, and isn’t as easy to use. But it has the ability to convert image files with worldfiles into GeoTiffs, and export image files with worldfiles, but without the stamped message at the bottom. It also has a limited ability to embed coordinate/datum data into the GeoTiffs along with the georeferencing data.

To convert an image file with a worldfile:

1. From the File=>Open menu, choose either “Open image” or “Open scanned map”

2. From the “Files of type” dropdown, choose “Imagery with world files”

3. Select the worldfile for the image you want to open (e.g. *.tfw, *.jgw, etc.)

4. The “Pick Projection Parameters” window will open. Here you can select the datum for the data, and the UTM zone for UTM coordinates. If the worldfile is in geographic coordinates (lat/long), the UTM Zone setting is irrelevant.

Capture8-14-2007-1.31.17 PM8-14-2007-10.47.04 PM9-11-2007-7.24.32 PM

5. Click OK, and the image will open onscreen, fully georeferenced. If you only want to export part of the image, you can select it with the subset and zoom button on the toolbar:


6. MicroDEM saves images in the screen resolution; to save in the full native resolution, you’ll have to zoom to 1:1; to do that, click on the “No zoom (1:1)” toolbar button:


7. Choose File => Save map as image => GEOTIFF, screen scale. This will save the image as a GeoTiff, with the georeferencing data embedded, and with the coordinate system and WGS84 datum information also embedded. And no watermark stamp.


– JPG, BMP, GIF and PNG supported natively; MRSid is supported with add-ons, but isn’t easy to work with. Search the help file for “MRSid” for more info on how to set this up in MicroDEM.

– The only coordinate systems supported are geographic and UTM; no Lambert, SPCS, etc..

– The only datum data is exported in is WGS84, regardless of what datum the original data was in, and which datum you specified in step 4 above.

– GeoTiffs are exported in 24-bit color; 8-bit or indexed color is not supported.

If you want to go the other direction, converting a GeoTiff or MRSid file with embedded geodata into an image format with worldfile:

1. Open the GeoTiff/MRSid in MicroDEM

2. Select File => Save map as image => With worldfile

3. Select the desired image format (BMP, PNG or JPG), and save the file. The worldfile will be created automatically in the same directory.

Stand-Alone Map Projection Viewers III – MicroDEM

In addition to its primary terrain analysis functions, MicroDEM also has a number of map projection viewing features, accessible by opening a vector map from the File => Open => Vector Map menu, or clicking on the “Open vector map” button on the top toolbar:


This brings up the “Map Projections” window:

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Creating GeoTiffs From TerraServer Imagery With MicroDEM

TerraClient offers a fast and simple way to get TerraServer black-and-white aerial imagery covering large areas, but with no georeferencing data that lets it be used directly in a GIS. USAPhotoMaps offers a convenient and easy interface for downloading TerraServer topo and aerial imagery of smaller areas, with georeferencing data in worldfile format. But the USAPhotoMaps images are saved in JPEG format resulting in some minor image quality degradation, and the worldfile data doesn’t include information like the coordinate system and datum. For that, you’d want to have the TerraServer imagery saved in a format that embeds georeferencing, coordinate system and datum into the actual file format, like GeoTiffs. MicroDEM offers the ability to download TerraServer imagery and then save it in GeoTiff format. While the process and interface are a bit more convoluted than that for USAPhotoMaps or TerraClient, it’s not too bad.

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Determining 3D Distance Traveled Over Terrain

Most free GIS programs have a measuring tool that lets you determine the distance between two or more points. But this distance is usually a flat, straight-line distance, and doesn’t take into account the additional distance you would travel if the terrain weren’t flat. If the terrain is steep or hilly, your 3D distance traveled is longer than that flat, straight-line distance.

MicroDEM has the capability to determine both the straight-line distance and distance over terrain for an arbitrary path. After loading in a digital elevation model (DEM), click on the Distance (stream selection) in the window’s toolbar:


Then draw the path on your DEM:


And MicroDEM brings up a window with the flat distance, and 3D distance over terrain:


If you have a map whose area is covered by the DEM, you can draw the path directly on the map:


MicroDEM links the map with the DEM, and will calculate the straight-line and 3D distances:


Cartographic Utilities In MicroDEM: Datum Shift, Magnetic Declination, UTM Grid Deviation From True North, And Sunrise/Sunset/Twilight Times

While its primary functions deal with DEM/terrain display and analysis, MicroDEM has some handy cartographic functions as well for any position on a georeferenced map. It can calculate the amount of shift in position between different datums for both UTM and geographic coordinates; determine the current angular variation between true and magnetic north; find the deviation from true north for the UTM grid, and label sunrise/sunset/twilight times for multiple points on a map.

More after the fold …

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LIDAR Data Coastal Erosion And Flooding Analysis Using MicroDEM

LIDAR (Light Detection and Ranging) can be used to create high-resolution terrain data (sub-meter), detail good enough to show individual man-made features like buildings and bridges. It’s especially useful for analyzing terrain in areas that are in constant change, like coastlines. High-resolution coastal LIDAR data is available at this NOAA website for the entire US ocean coastline, and parts of the Great Lakes coastlines, for times ranging from 1996 to the present.

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The "Inconvenient Truth" Effect In Google Earth: Animated Sea Level Rise Flooding Of Lower Manhattan With An Added Depth Effect

Yesterday’s post showed how to create a sea level rise flooding animation in Google Earth, like this one:

But if you downloaded the KMZ file used to create this animation, and ran it with 3D buildings turned on at the tip of Manhattan, the final image you’d get with 12 meters of flooding looks like this:


And there’s a problem with the accuracy of this image: there’s no actual depth to the flooding, i.e. the lower levels of the buildings aren’t covered with water. In fact, some of the buildings you can see in the view above would be completely covered with water if this were a more realistic depiction. That’s because no absolute altitude was assigned to the image overlays used in creating the animation, so they are “clamped” to the terrain level. But by assigning a height to every overlay image in the animation, one can create a realistic effect where the flooding doesn’t just cover more area as the sea level rises, but covers the bottom levels of some buildings, and completely covers other ones. This would be similar to the animations shown in the movie “An Inconvenient Truth”, and in one sense even better. In that movie, the flooding was show in overhead views, while the Google Earth animation can be viewed at an oblique angle of your choosing, with 3D buildings.

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