The Classify Land Use command is used to geospatially analyze an orthophoto and then classify land use based upon an automated color segmentation method, creating a thematic land use layer. An orthophoto is an aerial image that has been geometrically corrected, or ‘ortho-rectified,’ so that the scale is uniform and may be used similarly to a map.
The user first trains the software to recognize various land types based upon selected target areas on the orthophoto. The software reviews the colors and patterns of the selected targets, and then segments the remaining orthophoto into regions to match selected targets using raster recognition. From this, it merges adjacent matching land use regions and creates a thematic land use layer, as shown below.
From the Input ribbon menu, select the Classify Land Use command. Selecting this command causes the following panel to be displayed floating to the right side of the Map View.
When selecting this command, if the Map View is in 3D view mode (even if viewing from directly above) the software will force the Map View into 2D view mode. This is because the Map View must be in 2D mode to perform this task.
Note that prior to using this command, the user need to assign a CRS to the project. Refer to this article in our knowledge base to learn about how to assign a coordinate reference system to a project.
The various subsections of the Classify Land Use panel are discussed below.
The General Specifications section of the Classify Land Use panel is used to define the following properties:
Land Use Layer
This entry is used to define the land use layer to add the land use polygon data. Clicking on the pencil icon will allow the user to rename the selected land use layer. In addition, at the top of the listing is an Add New Layer entry which will create a new layer.
Land Use Layer Transparency
This option is used to adjust the transparency of the land use being painted using the horizontal slider, allowing the user to see through the defined land use areas to the underlying displayed map. Default transparency value is 50%.
Image Training Layer
This option is used to define the image source and extents of the training layer. Clicking on the [Define] button will cause the software to open the Define Image Training Layer dialog box.
- Image Source Selection
The Image Source Selection section allows the user to select an image source from the dropdown combo box and the zoom level to be used to create the image training layer by zooming in and out of the base map.
- Land Use Training Limits
The Land Use Training Limits section allows the user to define the land use limits using three different options: current screen limits, user-defined limits, and HEC-HMS model extents.
- Image Training Layer Specifications
The Image Training Layer Specifications section allows the user to define the image training layer. The Overwrite existing image training layer is checked by default to automatically overwrite any existing image training layer.
The Classification Training section of the Classify Land Use panel is used to train the software to recognize various land uses for the loaded orthophoto imagery.
The following details how to train the software to classify land uses from the loaded orthophoto imagery.
The Pick Sample tool is used to train the software to recognize land use areas from the loaded orthophoto imagery.
To use the Pick Sample tool, follow these steps:
- Select the Pick Sample tool. The sampling cursor is round, and the size can be adjusted if desired.
- Select the appropriate land use from the Land Use Palette to identify on the Map View.
- Position the nib pointer on the Map View where you want to start sampling.
- Choose locations on the loaded orthophoto imagery that match the selected land use. The more training samples selected, the better the software will be trained to recognize land uses from the orthophoto imagery.
- Press and hold down the mouse button to paint-in areas where samples should be taken from. As you drag the nib pointer around the Map View, the land use training sample area is painted in real time.
- Now, release the mouse button. After a sample has been selected, the software will create an equivalent polygon at the sample location matching the painted-in sample area.
If more training sample area needs to be added to an existing sample, simply start painting-in more sample areas. Where a new training sample area overlaps an existing sample area, the areas are merged into a single polygon.
The following observations apply to the Pick Sample tool:
- The Land Use Palette shows the number of training samples that have been selected for each land use.
- The Pick Sample tool is always in overwrite mode. It overwrites any existing overlapping sample polygons.
The Erase Sample tool can be used to erase all or part of a land use sample polygon area.
To use the Erase Sample tool, follow these steps:
- Select the Erase Sample tool.
- Position the nib pointer on the Map View where you want to start erasing a land use sample.
- Press and hold down the mouse button to erase.
- Drag the nib pointer around the land use sample area that is to be erased.
- On releasing the mouse button, the land use sample area traced by the nib will be erased. The software will convert the remaining area into a land use sample polygon.
The following observation applies to the Erase Sample tool:
- Creation of interior holes (doughnuts) is supported when erasing land use sample areas. For example, the user may erase the park area that is surrounded on all sides by a street land use.
The Sampling Size slider allows the user to adjust the nib size used to select training samples from the loaded orthophoto imagery.
Clear All Land Use
The [Clear All Land Use] button causes the software to remove the classified land use polygon areas from the Map View. This command allows the user to iteratively select training samples to better inform the software how to classify land use areas from the loaded orthophoto imagery.
Classify Land Use
The [Classify Land Use] button causes the software to classify land use polygon areas from the loaded orthophoto imagery based upon the defined training samples.
Filter Out Isolated Pixel Areas
This entry is checked by default. This checkbox entry causes the software to reclassify small, isolated regions of pixels that might give a “salt and pepper” or speckled appearance to the nearest land use classes. Small regions with pixel count less than or equal to the defined pixel threshold will disappear; being essentially dissolved away based on the closest surrounding cell land use types. A default threshold value of 50 pixels is provided.
Land Use Palette
- The […] lookup button is used to define the curve numbers for the specified land use. Clicking on this button will display a Select Curve Numbers lookup table dialog box.
- The Impervious (%) column displays the imperviousness associated with a specific land use or land type.
- The Training Samples column displays the number of training samples assigned to each defined land use.
The following button commands are listed at the bottom of the land use palette.
Land Use Properties
The Land Use Properties dialog box allows the user to define various land uses and their properties, style the border associated with the land use polygon, change the image’s transparency, and display the land use legend in the Map Data Layers panel and/or on the Map View. Furthermore, it also allows the user to change the current CRS (coordinate reference system) of the project and automatically apply the transformation scale factor on any particular layer to accurately map it to the project CRS. Refer to this article in our knowledge base to learn more about the Land Use Properties.