Discovery API: Image previews

Overview

API Multi Catalog - Getting the Images Overview

Getting quicklooks

URL pattern

Links like http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/QL/<id> returns a “quicklook” (i.e. a sub sampled image of the acquisition) of the scene or datastrip whose identifier is <id>.
http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/<id> is also allowed.

The width of the quicklooks is approximately 500 pixels; the height depends on the length of the acquisition.
The image format is standard JPEG.

No SLA key is required.

Quicklook simple URL follows this pattern:

  • A service address: http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/QL/
  • An imagery identifier (an alphanumeric string).

A more complex and powerful syntax is also available:

  • A service address: http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?
  • An imagery identifier (an alphanumeric string);
  • A query string made of key/value pairs separated by ampersands to ask for specific processing.

Cache-friendly simple syntax

  • http://api.astrium-geo.com/catalog/img/getfeatureImage.aspx/QL/DS_PHR1A_201204082024066_FR1_PX_W152S17_0413_01804
  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/DS_PHR1A_201204082024066_FR1_PX_W152S17_0413_01804

API Multi Catalog - Figure 13 - DS_PHR1A_201204082024066_FR1_PX_W152S17_0413_01804  
Figure 13 - DS_PHR1A_201204082024066_FR1_PX_W152S17_0413_01804

Powerful syntax (asking for a crop for instance)

Using a query string makes it possible to ask for some processing, for instance cropping:

  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?id=DS_PHR1A_201204082024066_FR1_PX_W152S17_0413_01804&bboxuly=200&bboxulx=200&bboxlry=500&bboxlrx=500

API Multi Catalog - Figure 14 – crop of DS_PHR1A_201204082024066_FR1_PX_W152S17_0413_01804  
Figure 14 – crop of DS_PHR1A_201204082024066_FR1_PX_W152S17_0413_01804

Pay attention that a misspelled key is silently ignored (for instance “&bboxul=200” instead “&bboxuly=200” makes the criterion to be ignored and set to 0), look at the difference below:

API Multi Catalog - Figure 15 – misspelled “bboxuly” key  
Figure 15 – misspelled “bboxuly” key

 

Supported identifiers

See § SPOT 1-5, PHR and SPOT 6 identifiers for a comprehensive unveiling of each satellite family imagery IDs.

SPOT 1-5 scene business identifier (“A21 code”)

Using A21 code, native scene (10m color):
  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/QL/53164191202280210532J
  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/53164191202280210532J
  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?id=53164191202280210532J
  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/QL/S_54973830604292026421J_3906648
  • http://daliis.spotimage.fr/wstools/img20/getfeatureimage.aspx/QL/S_54973830604292026421J_3906648_Shift0

Figure 16 – SPOT scenes 53164191202280210532J and 53164191202280210532U, no shift

API Multi Catalog - Figure 16 – SPOT scenes 53164191202280210532J and 53164191202280210532U, no shift
Using A21 code, combined scene (pan-sharpened 2.5m color):
  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/QL/53164191202280210532U
  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/53164191202280210532U
  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?id=53164191202280210532U
Using A21 code, 10% shift:
  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/QL/53164191202280210532U_Shift1
  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/53164191202280210532J_Shift1
  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?id=53164191202280210532J_Shift1

Figure 17 – SPOT scenes 53164191202280210532J and 53164191202280210532U, 10% shift

API Multi Catalog - Figure 17 – SPOT scenes 53164191202280210532J and 53164191202280210532U, 10% shift

 

SPOT 1-5 scene internal identifier (just for the record)

Native scene:

  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/S_37030427
  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/S_37030427_Shift0
  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?id=S_37030427_Shift0

Native scene, 10% shift:

  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/S_37030427_Shift1
  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?id=S_37030427_Shift1

Combined scene:

  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/C_23359337
  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/C_23359337_Shift0
  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?id=C_23359337

Combined scene, 30% shift:

  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/C_23359337_Shift3

SPOT 1-5 datastrips (experts)

Native datastrip, using A26 ID:

  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/QL/D/S5G1J201209220528063IJIJDT
  • http://api.astrium-geo.com/catalog/img/getfeatureImage.aspx?DT=D&IT=QL&CP=F&ID=7429445&sd=t
  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/QK/D/S5G1J201209220528063IJIJDT
  • http://api.astrium-geo.com/catalog/img/getfeatureImage.aspx?DT=D&ID=S5G1J201209220528063IJIJDT

Native datastrip, using internal ID:

  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/QL/D/7429445
  • http://daliis.spotimage.fr/wstools/img21/getfeatureImage.aspx?DT=D&CP=N&ID=7429445

SPOT 6

See § SPOT 6 identifiers for a comprehensive description of SPOT 6 IDs.

SPOT 6 datastrip quicklook, using casual ID:

  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/DS_SPOT6_201302171114555_FR1_FR1_FR1_FR1_W016N11_01546

PHR

See § PHR identifiers for a comprehensive description of PHR IDs.

PHR datastrip quicklook, using casual ID:

  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/DS_PHR1A_201204040917388_FR1_PX_E018N04_0709_01211

Cropping quicklooks (PHR and SPOT 6)

Cropping is not compatible with GeoTIFF format output. SPOT 1-5 quicklooks cannot be cropped. 

Cropping using geographical coordinates

The crop rectangle is defined by its opposite northwest and southeast corners given in WGS-84 lat/long:

  • Northwest latitude: 35.27
  • Northwest longitude: -2.92
  • Southeast latitude: 35.07
  • Southeast longitude: -2.76

The crop is provided by the following link:

  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?
    ID=DS_PHR1A_201204231052105_FR1_PX_W003N35_0207_03316&bboxnwlat=35.27&bboxnwlong=-2.92&bboxselat=35.07&bboxselong=-2.76

Cropping rectangle coordinates default to the quicklook border coordinates when not provided:

  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?ID=DS_PHR1A_201204231052105_FR1_PX_W003N35_0207_03316&bboxselat=35.27&bboxselong=-2.93

Quicklooks

Complete PHR quicklook:

API Multi Catalog - Complete PHR quicklook
Cropped PHR quicklook:

API Multi Catalog - Cropped PHR quicklook

 

Query string

Key Criteria Value
bboxnwlat Crop rectangle Northwest latitude decimal latitude, from -90 to +90. When omitted, image north border latitude is used.
bboxnwlong Crop rectangle Northwest longitude decimal longitude, from -180 to +180. When omitted, image west border longitude is used.
bboxselat Crop rectangle Southeast latitude decimal latitude, from -90 to +90. When omitted, image south border latitude is used.
bboxselong Crop rectangle Southeast longitude decimal longitude, from -180 to +180. When omitted, image est border longitude is used.

Results come as JPEG (default output format).

API Multi Catalog - Cropped PHR quicklook

Cropping using image coordinates

We use the previous example.

The crop rectangle is defined by its opposite upper left and lower right corners given in quicklook pixel coordinates - (0, 0) is the quicklook upper left corner:

  • Upper left abscissa: 293
  • Upper left ordinate: 920
  • Lower left abscissa: 823
  • Lower left ordinate: 1714

The crop is provided by the following link:

  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?ID=DS_PHR1A_201204231052105_FR1_PX_W003N35_0207_03316&bboxuly=920&bboxulx=293&bboxlry=1714&bboxlrx=823

Cropping rectangle coordinates default to the quicklook border coordinates when not provided:

  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?ID=DS_PHR1A_201204231052105_FR1_PX_W003N35_0207_03316&bboxlry=924&bboxlrx=261

Query string

Key Criteria Value
bboxulx Crop rectangle upper left abscissa Positive integer value. When omitted, assumed to be 0.
bboxuly Crop rectangle upper left ordinate Positive integer value. When omitted, assumed to be 0.
bboxlrx Crop rectangle lower right abscissa Positive integer value. When omitted, assumed to be the rightmost image column.
bboxlry Crop rectangle lower right ordinate Decimal longitude, from -180 to +180. When omitted, assumed to be the bottommost image column.

Results come as JPEG (default output format).

Getting GeoTiff quicklooks

GeoTIFF output, re-projection and cropping are exclusive functionalities.
SPOT 1-5 masks are not supported.

Examples of URLs & Query string

PHR quicklook:

  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?id=DS_PHR1A_201204040917388_FR1_PX_E018N04_0709_01211&ft=tif

SPOT 6 quicklook:

  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?id=DS_SPOT6_201302171114555_FR1_FR1_FR1_FR1_W016N11_01546&ft=tif

SPOT 5 datastrip quicklook:

  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?DT=D&IT=QL&ID=S5G1J201209220528063IJIJDT&ft=tif

SPOT 5 scene quickone with histogram stretching:

  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?id=53164191202280210532J&sd=T&WP=0&BP=10&IT=QK&ft=tif

​Query string

Key Criteria Value
ft Output format tif (quicklook and quickone only, no mask)

Results come as JPEG (default output format).

Re-projecting quicklooks

GeoTIFF output, re-projection and cropping are exclusive functionalities.
SPOT 1-5 masks re-projection is not supported.
The target CRS (Coordinate reference system) is referred by using its EPSG code.

Supported CRS are:

  • 3857, Spherical Mercator projection coordinate, used by OpenStreetMap, Google Maps and the like ;
  • 32662, Plate Carrée, this projection maps x to be the value of the longitude and y to be the value of the latitude ;

Other CRS can be added on request.

Examples of URLs & Query string

PHR quicklook:

  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?id=DS_PHR1A_201204040917388_FR1_PX_E018N04_0709_01211&pr=3857

SPOT 6 quicklook:

  •  http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?id=DS_SPOT6_201302171114555_FR1_FR1_FR1_FR1_W016N11_01546&pr=32662

SPOT 5 datastrip quicklook:

  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?DT=D&IT=QL&ID=S5G1J201209220528063IJIJDT&pr=3857

SPOT 5 scene quickone with histogram stretching:

  • http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?id=53164191202280210532J&CP=F&BN=2&sd=T&WP=3&BP=5&IT=QL&pr=3857

​Query string

Key Criteria Value
pr CRS SRID – coordinate system identifier EPSG code

Results come as JPEG (default output format).

Shifting SPOT 1-5 quicklooks

SPOT 1-5 acquisitions are split into scenes. Due to a land based fixed grid boundary computation, SPOT 1-5 scenes often need to be shifted to center an area of interest (AOI).
This shift is called SAT (Shift Along the Track).
See § “More about SPOT 1 to 5 specific characteristics” for a comprehensive explanation.
Incomplete scene quicklooks are filled with a black strip in order to be fixed-size 500x500 pixels image.

The SAT value is concatenated to the scene id:

  • “_Shift0”: no shift;
  • “_Shift1”: 10% shift;
  • “_Shift9”: 90% shift.

The SAT value has to fall between the min and max values allowed for a given scene (not necessarily 0 and 9).

Examples of URLs & Query string

Canonical URL:

  • A21 ID :
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/QL/53164191202280210532J_Shift1
  • A21 ID + datastrip number (native scene only):
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/QL/S_53164191202280210532J_7141440_Shift1

Short URL:

  • A21 ID :
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/53164191202280210532J_Shift1
  • A21 ID + datastrip number (native scene only):
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/S_53164191202280210532J_7141440_Shift1

Query string to allow some extra processing (false-color for example):

  • A21 ID, using SF (shift) key:
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?ID=53164191202280210532J&SF=1&CP=F
  • A21 ID, shift is concatenated to the identifier:
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?ID=53164191202280210532J_Shift1&CP=F
  • A21 ID + datastrip number (native scene only):
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?ID=S_53164191202280210532J_7141440_Shift1&CP=F

​Query string

Key Criteria Value
SF Shift Range [0, 9], has to fall between the actual scene min and max values

Results come as JPEG (default output format).

Getting SPOT 1-5 cloud or snow masks

SPOT 1-5 acquisitions are split into scenes. Due to a land based fixed grid boundary computation, SPOT 1-5 scenes often need to be shifted to center an area of interest (AOI).
This shift is called SAT (Shift Along the Track).
See § “More about SPOT 1 to 5 specific characteristics” for a comprehensive explanation.
Incomplete scene masks are filled with a black strip in order to be fixed-size 500x500 pixels image.

The SAT value is concatenated to the scene id:

  • “_Shift0”: no shift;
  • “_Shift1”: 10% shift;
  • “_Shift9”: 90% shift.

The SAT value has to fall between the min and max values allowed for a given scene (not necessarily 0 and 9).

Examples of URLs & Query string

Cloud mask canonical URL:

  • A21 ID :
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/CLD/53164191202280210532J_Shift1
  • A21 ID + datastrip number (native scene only):
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/CLD/S_53164191202280210532J_7141440_Shift1

Figure 18 – SPOT 53164191202280210532J, 10% shift (Australia)

API Multi Catalog - Figure 18 – SPOT 53164191202280210532j 10percent
Snow mask canonical URL:
  • A21 ID :
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/SNW/40522571212240914171I_Shift2
  • A21 ID + datastrip number (native scene only):
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/SNW/S_40522571212240914171I_7566893_Shift3

Figure 19 – SPOT scene 40522571212240914171I, 30% shift (Alps Mountains)

API Multi Catalog - Figure 19 – SPOT 40522571212240914171i 30 percent
Cloud mask URL using a query string to allow some extra processing (setting the output format to Windows BMP or JPEG):
  • A21 ID, using SF (shift) key, Windows BMP output:
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?IT=CLD&ID=53164191202280210532J&SF=1&FT=BMP
  • A21 ID, shift is concatenated to the identifier, JPEG output:
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?IT=CLD&ID=53164191202280210532J_Shift1&FT=JPG
  • A21 ID + datastrip number (native scene only), output default to JPEG:
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?IT=CLD&ID=S_53164191202280210532J_7141440_Shift1
Snow mask URL using a query string to allow some extra processing:
  • A21 ID, using SF (shift) key, Windows BMP output:
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?IT=SNW&ID=40522571212240914171I&SF=1&FT=BMP
  • A21 ID, shift is concatenated to the identifier, JPEG output:
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?IT=SNW&ID=40522571212240914171I_Shift1&FT=JPG
  • A21 ID + datastrip number (native scene only), output default to JPEG:
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?IT=SNW&ID=S_40522571212240914171I_7566893_Shift1

Query string

Key Criteria Value
IT Image Type CLD (Cloud) , SNW (Snow), QK (Quickone), QL (Quicklook)

 

Getting SPOT 1-5 false color quicklooks

Quicklooks, examples of URLs & Query string

Query string URLs:
  • A21 ID, no shift:
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?ID=53164191202280210532J&CP=F
  • A21 ID, shifted:
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?ID=40522571212240914171I_Shift3&CP=F
  • Datastrip:
    http://api.astrium-geo.com/catalog/img/getfeatureImage.aspx?DT=D&IT=QL&ID=S5G1J201209220528063IJIJDT&CP=F

Figures 20 and 21 – false-color SPOT scenes and datastrip

API Multi Catalog - Figure 20 – False-color SPOT scenes  
Figure 20  
API Multi Catalog - Figure 21 – False-color SPOT datastrip  
Figure 21

Query string

Key Criteria Value
CP Color Processing F (False color), N (pseudo-natural), SB (spectral band extraction)

Results come as JPEG (default output format).

Getting SPOT 1-5 extraction of individual spectral bands

Quicklooks, examples of URLs & Query string

API Multi Catalog - Figure 22 – spectral bands of SPOT 5 “53164191202280210532J” scene  
Figure 22 – spectral bands of SPOT 5 “53164191202280210532J” scene
Query string URLs:
  • A21 ID, no shift, spectral band #4 (MIR):
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?ID=53164191202280210532J&CP=SB&BN=3
  • A21 ID, shifted, spectral band #1:
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?ID=40522571212240914171I_Shift3&CP=SB&BN=0
  • Datastrip,  spectral band #2, quickone:
    http://api.astrium-geo.com/catalog/img/getfeatureImage.aspx?DT=D&IT=QK&ID=S5G1J201209220528063IJIJDT&CP=SB&BN=1

Query string

Key Criteria Value
CP Color Processing F (False color), N (pseudo-natural), SB (spectral band extraction)
BN Band Number [0, 3], increasing wavelength.

Results come as JPEG (default output format).

Getting SPOT 1-5 quickone

SPOT 1-5 acquisitions are split into scenes. Due to a land based fixed grid boundary computation, SPOT 1-5 scenes often need to be shifted to center an area of interest (AOI).
This shift is called SAT (Shift Along the Track).
See § “More about SPOT 1 to 5 specific characteristics” for a comprehensive explanation.
Incomplete scene quickone are filled with a black strip in order to be fixed-size 125x125 pixels image.

The SAT value is concatenated to the scene id:

  • “_Shift0”: no shift;
  • “_Shift1”: 10% shift;
  • “_Shift9”: 90% shift.

The SAT value has to fall between the min and max values allowed for a given scene (not necessarily 0 and 9).

Examples of Quickone, URLs & Query string

Quickone canonical URL:

  • A21 ID :
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/QK/53164191202280210532J_Shift1
  • A21 ID + datastrip number (native scene only):
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/QK/S_53164191202280210532J_7141440_Shift1
  • Datastrip:
    http://api.astrium-geo.com/catalog/img/getfeatureImage.aspx/QK/D/S5G1J201209220528063IJIJDT

Figure 23 – SPOT 53164191202280210532J, 10% shift (Australia)

Quickone access using a query string to allow some extra processing:

  • A21 ID, no shift, false color:
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?IT=QK&ID=53164191202280210532J&SF=1&CP=F
  • A21 ID, 10% shift, GeoTiff output:
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?IT=QK&ID=53164191202280210532J_Shift1&FT=TIF
  • A21 ID + datastrip number (native scene only), no histogram stretching :
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?IT=QK&ID=S_53164191202280210532J_7141440_Shift1&SD=F
  • A21 ID, spectral band extraction:
    http://api.astrium-geo.com/catalog/img/getfeatureImage.aspx?DT=D&IT=QK&ID=S5G1J201209220528063IJIJDT&CP=SB&BN=1
API Multi Catalog - Figure 23 – SPOT 53164191202280210532j shift 10%

Query string

Key Criteria Value
IT Image Type CLD (Cloud) , SNW (Snow), QK (Quickone), QL (Quicklook).

Results come as JPEG (default output format).

Getting SPOT 1-5 datastrips

Examples of datastrips quicklooks, URLs & Query string

  API Multi Catalog - Figure 24 – SPOT datastrip quicklook (standard, white point set to 50%, MIR band, cloud mask
Figure 24 – SPOT datastrip quicklook (standard, white point set to 50%, MIR band, cloud mask)
Datastrip canonical URL:
  • Quicklook:
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/QL/D/S4I1I201212240914102TTTTDT
  • Quickone:
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/QK/D/S4I1I201212240914102TTTTDT
  • Cloud mask:
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/CLD/D/S4I1I201212240914102TTTTDT
  • Snow mask:
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx/SNW/D/S4I1I201212240914102TTTTDT
Datastrip access using a query string to allow various processing:
  • GeoTIFF output:
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?IT=QL&ID=S4I1I201212240914102TTTTDT&DT=D&SD=T&FT=TIF
  • Geographical projection:
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?IT=QL&ID=S4I1I201212240914102TTTTDT&DT=D&SD=T&PR=4326
  • Dynamic stretching:
    http://api.astrium-geo.com/catalog/img/getfeatureimage.aspx?IT=QL&ID=S4I1I201212240914102TTTTDT&DT=D&SD=T&WP=50

Query string

Key Criteria Value
DT Data strip Type D

Results come as JPEG (default output format).

Adjusting SPOT 1-5 quicklook histogram

Contrast enhancement

When stretching an image histogram, the image contrast can be accurately controlled using black and white point percentages. Use this option to set the black (resp. white) point at the minimum intensity (0%), or to choose the black (resp. white) point such as some percentage of the pixels in the image is below the black point (or over the white point).

Contrast enhancement table

Quicklook Histogram Associated URL
API Multi Catalog - Quicklook 1 API Multi Catalog - Histogram 1
Quicklok histogram
No histogram stretching.
URL : ID=51062690608150844012A&IT=QL&SD=F
API Multi Catalog - Quicklook 2 API Multi Catalog - Histogram 2a
Transformation
  API Multi Catalog - Histogram 2b
Resulting histogram
Default histogram stretching: white and black points valued at 2%.
URL : ID=51062690608150844012A&IT=QL&SD=T
API Multi Catalog - Quicklook 3 API Multi Catalog - Histogram 3 No histogram clipping, just an image histogram stretching:
  • Black point: 0%
  • White point : 0%
The little cloud, on the left, is saturated and “freezes” the histogram expansion on the “right”.
No information is lost but the resulting-image contrast is poor.
URL : ID=51062690608150844012A&IT=QL&SD=T&BP=0&WP=0
API Multi Catalog - Quicklook 4 API Multi Catalog - Histogram 4 A little “white” clipping to clear the cloud impact and get a quicklook with a better contrast:
  • Black point: 0%
  • White point : 1%
URL : ID=51062690608150844012A&IT=QL&SD=T&BP=0&WP=1
API Multi Catalog - Quicklook 5 API Multi Catalog - Histogram 5 Some heavy histogram clipping of no practical use:
  • Black point: 10%
  • White point : 20%
URL :ID=51062690608150844012A&IT=QL&SD=T&BP=100&WP=20
API Multi Catalog - Quicklook 6 API Multi Catalog - Histogram 6 A pseudo color image.
No histogram stretching.
URL : ID=51062750608150844532J&IT=QL&SD=F
API Multi Catalog - Quicklook 7 API Multi Catalog - Histogram 7 Default histogram stretching:
white and black points valued at 2% for each spectral band.
Stretching is performed separately on each spectral band.
Some color shift can occur on pseudo natural color images
URL : ID=51062750608150844532J&IT=QL&SD=T
API Multi Catalog - Quicklook 8 API Multi Catalog - Histogram 8 No histogram clipping, just an image histogram stretching:
  • Black point: 0%
  • White point : 0%
The sparse clouds are saturated and “freeze” the histogram expansion on the “right”.
The lake surface or the cloud shadows contain some black blocking histogram expansion on the “left”.
No information is lost but the resulting-image contrast is low.
URL : ID=51062750608150844532J&IT=QL&SD=T&WP=0&BP=0
API Multi Catalog - Quicklook 9 API Multi Catalog - Histogram 9 A little “white” clipping to clear the cloud impact, some black clipping to get rid of the lake darkness make a quicklook with a better contrast:
  • Black point: 1%
  • White point : 1%
URL : ID=51062750608150844532J&IT=QL&SD=T&BP=1&WP=1

 

SPOT 1-5 image processing parameter table

Key Meaning Default value Values
IT Image type QL QK (quickone),
QL (quicklook),
CLD (cloud mask)
SNW (snow mask).
CP Color processing N F (false color composite)
N (pseudo-natural colors)
SB (spectral band). When using SB, BN key (band number) has to be specified.
BN Band number   0 to 3 (bands 1 to 4), used in conjunction with CP=SB
SD Dynamic stretching T T (true)
F (false)
BP Black point 2 Meaningful only when dynamic stretching is required.
Integer value.
Percentage of image pixels to be made pure black (0 intensity).
Image histogram is linearly stretched between the intensity value associated with this percentage and the white point.
WP White point 2 Meaningful only when dynamic stretching is required.
Integer value.
Percentage of image pixels to be made pure white (255 intensity).
Image histogram is linearly stretched between the intensity value associated with this percentage and the black point.
FT Mask format   JPG (JIFF file format)
BMP (IBM/Microsoft DIB file format).
CM Compression 75 JPG image quality, ranging from 0 (worst) to 100 (best). Image size rises as CM value increases.

These parameters can be combined with re-projection and GeoTIFF output.

More about SPOT 1 to 5 specific characteristic

API Multi Catalog | Data strip cut into 3 scenes

The DALI catalogue includes metadata and preview (so-called “Quick Look”) of all images acquired by SPOT 1 to SPOT 5 satellites, from 1986 up to now.
SPOT satellites acquire “data strips” of 60 kilometres swath when aiming at nadir. These data strips are split into 60 kilometres long scenes. There is an overlap between two adjacent scenes of data strip. This overlap depends on the latitude.
The scene is the order unit. Airbus Defence and Space sells only scenes (full scenes or scenes extracts). The data strip cannot be accessed.

Each scene can be shifted along the data strip by steps of 1/10th of scene.
The shift value must be chosen between its min and max values.
The max= 9 indicates that the next scene is full. A shift of 10 is not allowed, but it can be extracted approximately using the next scene.

API Multi Catalog | Diferents Shifts possible for a Scene

In the example on the right, the first scene is incomplete.

The first image line starts between shift 3 and shift 4. So, the first scene that can be ordered is scene n°1 with a shift of four. The first scene can be shifted until nine. The next scene is scene n°2 with a shift of one. As the last image line is in the middle of scene three, the max shift of scene 2 is 3.

There is a little overlap between scene 1 with shift 9 and scene 2 with shift 1, because of the size of the overlap between the two scenes.

There are two main receiving stations for SPOT data and a worldwide network of secondary receiving stations. The SPOT catalogue includes SPOT data received from all receiving stations. A given scene can be referenced several times in the SPOT catalogue, because of the visibility-circle overlap between different stations

However theses identical scenes, regarding to their localization, could have different quality quotations, depending on the environment of the receiving station. e.g.: one scene can be acquired at high elevation by one station while it is acquired at low elevation by another one.
Metadata describes the condition of acquisition: geographic localization, temporal range, optical instrument and sensor mode used and the technical conditions of the acquisition (in particular, angles).

The table below presents the optical instruments and sensors of each SPOT satellite and their associated characteristics of the previews:

SPOT 1-5 sensors and optical instruments

Satellite Optical instrument Sensor Colour Resolution in meters
SPOT 1 to SPOT 3 HRV P Black and white 10
X Colour 20
SPOT 4 HRVIR M Black and white 10
I Colour with SWIR 20
SPOT 5 HRG A Black and white 5
B Black and white 5
J Colour with SWIR 10

Airbus Defence and Space can deliver products with better resolution as shown in the table below when merging several scenes. These scenes are casually called “combined scenes”.

SPOT 1-5 sensor combinations

Satellite Optical instrument Sensor Colour Resolution in meters
SPOT 4 HRVIR M and I Colour 10
SPOT 5 HRG A and B Black and white 2,5
A and B and J Colour 2,5
(one of A, B) and J Colour 5