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Feature reader Geotiff GCP interpolation NO data values

  • 16 December 2015
  • 4 replies
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M
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In the feature reader there doesn't appear to be a way of setting all values outside of an image to nodata whilst performing GCP transformations. I'm using a geotiff within a featurereader to read mapinfo projected tiff files.

However, the resulting image (they are old maps so need to be re projected) should have a border of no data where the image is no long square. However, the feature reader fills this space with 0's not nodata. Is there a way of making the featurereader asign no data values during affine transformations?

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Best answer by mark2atsafe 16 December 2015, 16:20

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mark2atsafe
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Hi @marko - doesn't look like the GeoTIFF reader has that setting, inside or out of the FeatureReader. It sounds like a limitation of the Reader. The best way to proceed would be to log this issue with the support team (http://safe.com/support) - so it goes through official channels - and have them check with the developer. They might be able to come up with a quick workaround.

Hope this helps and apologies for any inconvenience.

M
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HI Mark,

Thanks for the reply.

I think using a tiff reader rather then the geotiff reader might help but sadly that wont pick up the geo referencing files and doesn't position the images correctly. I am pretty sure there wouldn't be any slow down in having a GIS or server warp the images on the fly to give the needed transform rather then embedding it into the geotiff, whcih would negate the need for no data around the edges. I will contact support and see what they say.

mark2atsafe
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So, our developers tell me this is a er... let's call it a shortcoming! If you have a nodata value set we ignore it and use zero instead. Not great. The good news is that it will be fixed in 2016.1 (it already is, but that version isn't available yet in beta or otherwise).

The only workaround I can really offer right now is to use FME2016.0 beta with the FeatureWriter transformer. You'd read the data (FeatureReader), add an alpha band, write it back (FeatureWriter), and finally read it in again. Let me know if that's of interest and I can work up an example workspace for you.

M
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Hi Mark,

Thanks for the reply. For some of the images I have been able to set the no data correctly as there isn't too many true black pixels in the image, but yes a better work around would be good moving forward. I will look into the 2016 in the new year and see what it has to offer. Mapinfo tabs files don't seem to work properly using a tiff reader and images are not located properly, if I can keep the images square and non transformed up until the geotiff writer that might solve the issue. I will also see if 2016 works with mapinfo geo referenced tiffs better. Thanks for your advice @Mark2AtSafe.

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