How to reproject rasters in Arcgis

Recalculate footprints through radiometry

Recommended parameter settings

The following table defines the various parameters that can be changed to adjust the footprints radiometrically.

parameter

description

Minimum data value

The lowest pixel value that represents valid image data. This value is determined by the bit depth of the raster dataset.

With 8-bit data, the values ​​can e.g. B. be between 0 and 255. A value around 0 represents very dark colors (for example, black frame pixels). If you specify 1, the only value less than 1 is 0. Therefore, all 0 values ​​are considered invalid data and are removed from the scope of the footprint. If the images are being compressed using a lossy compression method, you should define a value greater than 1 to remove all black pixels. Set a value less than the specified value if dark areas (e.g. shadows) were incorrectly removed from the footprint.

Maximum data value

Highest value that represents valid data. This value is determined by the bit depth of the raster dataset.

With 8-bit data, the values ​​can e.g. B. be between 0 and 255. A value around 255 represents very light colors (such as white clouds and snow). If you specify 245, all values ​​between 246 and 255 are removed from the scope of the footprint.

Approximate number of bases

Approximate number of vertices that will be used to create the new footprint polygon.

The minimum value is 4 and the maximum value is 10,000. The larger this value, the more precise and irregular the polygon and the longer the processing time.

You can also specify the value -1, which does not generalize the polygon footprint.

Decrease distance

Distance value specified in the coordinate system units for the mosaic dataset that reduces the size of the entire polygon.

Polygons are shrunk to counteract lossy compression that causes the edges of the image to overlap in NoData areas.

Request size

The size to which the raster will be resampled when examined using this process. The value (e.g. 2000) defines the dimension of rows and columns.

You can increase or decrease this value based on the complexity of your raster data. A larger image resolution provides more detail in the raster dataset, which increases processing time.

The minimum value is 0. The maximum value is 5000.

Minimum area size

Determines a filter that is used to remove holes created in the footprint.

This value is given in pixels and relates directly to the request size and not to the pixel resolution of the source raster.

Maintain sheet edges

Enable this option if you are using raster datasets that have been tiled and are stumped together (or strung along the boundaries with little or no overlap). An analysis of the edges of the image is carried out so that the edges of the sheet are not removed.

The following tables contain various types of datasets, which sometimes have NoData frames, and their recommended parameter settings.

Attention:

The zoom out distance below is defined by pixels, but the units of this parameter must be entered in the units of the coordinate system for the mosaic dataset. If the units are "meters", then each pixel is 10 meters and the recommended zoom out distance is 3; You should therefore enter 30.

Regularly and cut to size

Used for datasets in which the data pixels in each image form form a rotated rectangular area. The resulting images are cropped onto a new sheet or tile. Such datasets are typically created by reprojecting images or scenes and then cropping them onto map sheets or tiles with little or no overlap. The parameters are set so that the footprint only contains a few support points. An analysis of the edges is performed to maintain the sheet or tile boundaries.

parameter

No or lossless compression

Lossy Compression

Minimum data value

1

10

Maximum data value

254

245

Approximate number of bases

4

4

Decrease distance

2 pixels

6 pixels

Request size

1000

1000

Maintain sheet edges

Yes

Yes

Irregular and cut to the sheet

Used for datasets in which the data pixels do not form rectangular areas. The resulting images can be cropped onto map sheets or tiles. Such datasets are typical of imagery along pipelines or other linear features. Here the bitmap areas cover the linear feature, and the images are then mosaicked and cropped into tiles. The parameters are set to allow a larger number of support points that define the frame. An analysis of the edges of the resulting footprint is performed to maintain the leaf or tile boundaries.

parameter

No or lossless compression

Lossy Compression

Minimum data value

1

10

Maximum data value

254

245

Approximate number of bases

30

30

Decrease distance

6 pixels

6 pixels

Request size

1500

1500

Maintain sheet edges

Yes

Yes

Rotated rectangle

Used for images that form a rotated rectangle. Such datasets are typically created when individual scenes or sheets of maps have been rotated and the sides of the footprint remain straight. The parameters are set in order to define the footprint using only four support points.

parameter

No or lossless compression

Lossy Compression

Minimum data value

1

1

Maximum data value

254

245

Approximate number of bases

4

4

Decrease distance

2 pixels

6 pixels

Request size

1000

1000

Maintain sheet edges

No

No

Rectangle projected again

Used for rotated images that have been re-projected to form rectangular footprints with curved edges. Such datasets are typically created when individual scenes or map sheets have been re-projected. The parameters are set in order to define the footprint with a sufficient number of support points to represent the curves.

parameter

No or lossless compression

Lossy Compression

Minimum data value

1

10

Maximum data value

254

245

Approximate number of bases

20

20

Decrease distance

2 pixels

6 pixels

Request size

2000

2000

Maintain sheet edges

No

No

Orthocorrected image in flat terrain

Used when the origin of the raster dataset is a scene or image that has been orthorectified to flat terrain. The edges of such images form simple curves caused by smooth changes in height.

parameter

No or lossless compression

Lossy Compression

Minimum data value

1

10

Maximum data value

254

245

Approximate number of bases

30

30

Decrease distance

9 pixels

9 pixels

Request size

2000

2000

Maintain sheet edges

No

No

Orthocorrected image in hilly terrain

Used when the raster dataset is orthocorrected in an area that has large changes in elevation. The edges of such images are irregular, which is caused by sudden changes in height. More support points are required to define such footprints.

parameter

No or lossless compression

Lossy Compression

Minimum data value

1

10

Maximum data value

254

245

Approximate number of bases

200

200

Decrease distance

9 pixels

50 pixels

Request size

2000

2000

Maintain sheet edges

No

No

Minimum area size

The tables above do not suggest a default value for this parameter due to the potential complexity of this value. You need to consider the raster data and how detailed the footprint needs to be for your purposes.

The footprint is created to define the area of ​​the raster dataset that you want to display. The footprint is usually the extent of the raster dataset; however, it can be modified so that a user cannot view any part of the raster dataset.

The minimum and maximum data values ​​are used to indicate the valid dates. Outside of these values ​​is a range of pixel values ​​that are used to create a region or continuous feature in the raster dataset that creates a "hole" in the footprint polygon. For example, if you have a raster dataset with pixel values ​​from 0-255, you can define the valid range from 10-255. All pixels from 0 to 9 then form holes in the footprint. However, your image may have pixels from 0 to 9 that you want to keep because they represent valid features. You have to consider which ones that can be. For example, if the roof of a house is valid but is likely to be in the 0 to 9 pixel value range, you need to make sure that these values ​​do not result in holes in the footprint, whereas larger features, e.g. B. big clouds, do this.

The area of ​​the hole is compared with the calculated area using the minimum area size. If the area of ​​the hole is smaller than the area calculated using the minimum area size, the hole is removed. The minimal area size ensures that only large features are removed from the footprint by showing them as holes in the calculated geometry. All holes with an area smaller than the area specified by this parameter are removed. This means that they are no longer shown as holes in the calculated footprint. This ensures that small features are not cut out of the dataset.

In the following diagram, the gray pixel values ​​represent the valid data values. The orange pixels represent three regions in this raster that contain values ​​that you may want to exclude. The yellow fields represent the area defined by the minimum area size. The two orange areas on the left are smaller than the minimum area size. Therefore, the holes in the footprint polygon are removed and the pixels are not excluded. However, the large orange area on the right is larger than the minimum area size. Therefore, the hole in the footprint polygon is not removed and the pixels in the mosaic dataset are excluded from the mosaicked image.

When determining the minimum area size, the requirement size must also be taken into account, as this determines the resolution or the level of detail in the grid with which the footprint is recalculated. Typically, you will use a request size that is smaller than the dimensions of the original source raster. This affects the size of the area. For example, if you want to keep the roof area, you need to consider the pixel dimensions of the roof in the source raster and the dimensions in the request size. Therefore, if the roofs are 50 x 50 pixels in the source raster and the request size represents a raster that has 50% fewer pixels in its X and Y dimensions, the roofs may be represented by a feature of only 25 x 25 pixels. You need to know the minimum area size and the requirement size so that, on the one hand, you don't exclude features that you want to keep, but on the other hand, you exclude the features that are represented as holes in the footprint. In other words, you need to define the correct size to remove the small holes but keep the larger holes.