Rules for creating geometries

Geometry checklist

To successfully place tasking or catalog orders, your geometries must follow certain rules:

• Check that your geometries conform to the limitations specified for a particular tasking or catalog collection:

  • In Input, check whether the collection accepts AOIs or POIs.
  • In AOI size, check the upper and lower bounds of AOI sizes.
  • In Width and length, check the permissible ranges for the width and length of your AOI.

• Check that your geometries don't contain more than 999 vertices.

• If you're uploading your geometry as a file, make sure that it uses a supported file format.

• Verify that your geometry contains valid features.

Not valid features

Polygon or point features in geometries must meet certain validity conditions:

• Features that contain duplicate vertices aren't valid. These are features with one or more vertices that occur multiple times.

• Sliver polygons aren't valid. These are polygons with a very small area but with a very large perimeter.

• Self-intersecting polygons aren't valid. These are polygons whose edges cross each other.

• Polygons that intersect a catalog image footprint in more than one place aren't valid.

• Polygons that contain holes aren't valid.

Not valid

This polygon contains a hole and isn't valid.

An example of a polygon with a hole

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Valid

The polygon was split into two valid polygons.

An example of split polygons

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Correcting geometries in QGIS

You can resolve common geometry issues using QGIS, a free open-source GIS software. To do that, download and install QGIS. After the installation, open QGIS and then drag and drop your geometry files to edit them. For more information on how to use QGIS, see the QGIS documentation.

Check AOI size and number of vertices

1. In the top navigation menu, click Project →  Properties.
2. Inside the General panel, go to Measurements → Units for area measurement and select Square Kilometers. Click OK.
3. To display the Identify Results panel, in the top navigation menu, click View →  Identify Features.
4. Select the polygons you want to measure.
5. Inside the Identify Results panel on the right, click the polygon name and expand (Derived) to check the following:
   • In the Area (Ellipsoidal) field, check the size.
   • In the Vertices field, check the number of vertices.

Check for not valid features

Check for duplicate vertices, sliver polygons, self-intersections, and holes using the following steps:

1. To enable the geometry checking tool, in the top navigation menu, click Plugins → Manage and Install Plugins. Search for Geometry Checker and select the checkbox. Click Close.
2. In the top navigation menu, click Vector →  Check Geometries.
3. In Input vector layers, select your geometry file.
4. Check for not valid features as follows:
   • To check for self-intersections, in Geometry validity, select Self intersections.
   • To check for duplicate vertices, in Geometry validity, select Duplicate nodes.
   • To check for holes, in Geometry properties, select Polygons and multipolygons may not contain any holes.
   • To check for sliver polygons, in Geometry conditions, select No sliver polygons.
5. To modify your original geometry file, in Output vector layers, select Modify input layer.
6. Click Run to see the results of the geometry check.

Split a polygon

If your geometry file has a polygon that exceeds the AOI size limitations, has a hole, has self-intersections, is a sliver polygon, or intersects an image footprint in more than one place, you can split the polygon using the following steps:

1. To enable editing, in the top navigation menu, click Layer →  Toggle Editing.
2. In the top navigation menu, click  Select Features and then select the polygon you want to split.
3. In the top navigation menu, click Edit → Edit Geometry →  Split Features. Draw a line through the polygon, and right-click. This will split your polygon.
4. To modify your original geometry file, in the top navigation menu, click Layer →  Toggle Editing and Save.

Reduce the number of vertices

If your geometry file has a polygon with more than 999 vertices, you can reduce the number of vertices using the following steps:

1. To enable editing, in the top navigation menu, click Layer →  Toggle Editing.
2. In the top navigation menu, click Edit → Edit Geometry →  Simplify Feature and then select the polygon you want to simplify.
3. In Method, select Simplify by Distance and change values for Tolerance until the number of vertices goes below 999. Click OK.
4. To modify your original geometry file, in the top navigation menu, click Layer →  Toggle Editing and Save.

Remove holes

If your geometry file has a polygon with a hole, you can remove the hole using QGIS. Note this will increase the AOI size.

1. To display the Processing Toolbox, go to the top navigation menu and click Processing →  Toolbox.
2. In the Processing Toolbox search bar on the right, search for Delete holes and select it.
3. In Input layer, select your geometry file. Click Run and then Close.
4. Inside the Layers panel on the left, right-click on the new geometry file and click Export → Save Feature As.
5. In Format, select an accepted file type. Go to File name and click the ... button.
6. Specify the file name and directory you want to save your geometry file to. Click OK.

Remove duplicate vertices

If your geometry file has duplicate vertices or self-intersections, you can use the following steps:

1. To display the Processing Toolbox, go to the top navigation menu and click Processing →  Toolbox.
2. In the Processing Toolbox search bar on the right, search for Remove duplicate vertices and select it.
3. In Input layer, select your geometry file. Click Run and then Close.
4. Inside the Layers panel on the left, right-click on the new geometry file and click Export → Save Feature As.
5. In Format, select an accepted file type. Go to File name and click the ... button.
6. Specify the file name and directory you want to save your geometry file to. Click OK.