Ship Detection Land Sea Mask


#1

I have completed the OCEAN01 tutorial using the Gulf_of_Trieste_seamaks_UTM33.shp file. I have replaced this shapefile with a world_shorelines.shp file since I need to process other areas of the world. I had to invert the shape file since it was originally masking the water. I noticed that the mask was close to the edge of land so I used “Extend shoreline by Pixels” and this did not affect my results.

Question: Should the “Use Vector as Mask” and “Extend Shoreline by Pixels” both work together without problems? I did a very large pixel offset set of 100,000,000 and I did not see any change in my results compared with pixel offset of 10 when I had to use invert vector. Any suggestions?


#2

Unfortunately, it seems that it is not possible to combine the two options, although it would be useful. At he moment you can use the two following approaches:

  1. you can use the vector - perhaps you can use buffer in QGIS to create the shoreline extension, if your shapefile covers land then your buffer value would be positive (note that the buffer value is in projection units - example: UTM - meters; WGS84 - degrees) if your shapefile covers sea then the buffer value should be negative.

  2. you can use the SRTM (90 m resolution) with a shoreline extension (note that 100,000,000 is way larger than any actual image and the operator might not be able to process such value)


#3

Dear @tablewski
Yes you can use “Use vector as a map” and select your vector POLYGON as input. You can not select polygon layer as shore line.
For example you can use this layer:
http://openstreetmapdata.com/data/land-polygons
I have tested this layer and this is better than others and SRTM.
For example in Black Sea SRTM shows 29 m Hight.


#4

In Ocean Object Detection, I am using a world shape file for the Land-Sea-Mask by selecting “Use Vector as Mask”. The shape file needs to be inverted which works fine; however, I need to extend the shoreline by pixels which does not appear to work. Not sure I understand why I should “Use Vector as a map” instead of using Land-Sea-Mask.


#5

Hi

Where do I select “Use vector as a map”? I have downloaded land masking from http://openstreetmapdata.com/data/land-polygons and used it as a land mask with inversion and extending shore by 10 pixels. I notice that there is an offset between the image layer and the mask varying from .4 to .8 km. Is there a way to adjust the mask offset, see attached screen shot?


#6

Hi

I have switched to using water polygon from http://openstreetmapdata.com/data/water-polygons. I have extended out to 30 pixels for extended shoreline. I still have a lot of shore detects. Can you recommend a way where I can easily edit the detections. I am currently zooming into each circle and then looking at the X and Y value. I downloaded all the detections into a spreadsheet and sorted them by X value. I found 8 ship detections using this manual way and 2 of them correlated with AIS data.

Ship detections using water polygon with 30 pixel offset

Ship detections fused with AIS data


#7

You can either "Use Vector as a map” or “Land-Sea-Mask” it depend on accuracy of SRTM and your vector file.


#8

As I can see there is a huge offset between your vector and Raster. This is not normal and it is an error either in gerorefrencing of your Raster or accuracy of your Vector.
For the first one Are you using apply Orbit? If yes you can try different projection in Geo-Referencing
For the second one I can suggest checking your Vector file with GSHHG shorelines to be sure about accuracy of your vector. Or you can check it with SRTM to do so add elevation data to your product by right click on a band.


#9

Using offset for correcting a inaccurate/faulty georefrencing is not a good practice. Try suggested methods and come back to us if needed.


#10

Hi

I am still not able to extend the shoreline. I have the following setup:

  • http://openstreetmapdata.com/data/water-polygons (WGS84)

  • Applied orbit correction to Sentinal 1 GRDH image

  • Tried multiple combinations of “Extend shoreline by pixels” +50, -50, +500, -500. Changing the pixel extension does not affect the number of ship detects.

Question:
Is the extended land mask written out so I can check if it is actually affected?
Can I verify the options that are being sent to the ship detection software?

Thank You


#11

No extended land mask is not written
Which option do you mean?


#12

Did you test different vector and shore line data posted in previous answer ?
If yes, give URL of your Image.
I will test it myself if I found a spare time.