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How can I reproject this wms correctly?

hannahwh05
Contributor
Forum|alt.badge.img+5

I am trying to reproject a wms from the Environment Agency (https://environment.data.gov.uk/spatialdata/risk-of-flooding-from-surface-water-extent-0-1-percent-annual-chance/wms) from WGS 1984 to British National Grid. I need to know the cell size so I can provide a degree of accuracy of the data and have confidence in my areas of intersect calculations with some polygons. However, when I use the Reprojector, the spacing seems completely off. If I view it in ArcGIS Pro, the cell size appears to be 2m, which seems sensible. I have tweaked the parameters in the Reprojector but this doesn't give me the correct cell size. Any ideas what I'm doing wrong?

image

4 replies

daveatsafe
Safer
Forum|alt.badge.img+19
  • daveatsafeSafer
  • Safer
  • October 19, 2023

Hi @Hannah Wheldon​,

Most WMS viewer are interactive, so their requests automatically include the bounds of the view they will be displaying the image in. FME has no view, so you must manually set the bounds of the downloaded image in the WMS reader:

Screen Shot 2023-10-19 at 2.36.44 PMIf you try the settings shown above, you will get an image with a reasonable pixel spacing:

Screen Shot 2023-10-19 at 2.38.12 PMScreen Shot 2023-10-19 at 2.39.11 PM

hannahwh05
Contributor
Forum|alt.badge.img+5
  • hannahwh05Contributor
  • Author
  • Contributor
  • October 20, 2023
daveatsafe wrote:

Hi @Hannah Wheldon​,

Most WMS viewer are interactive, so their requests automatically include the bounds of the view they will be displaying the image in. FME has no view, so you must manually set the bounds of the downloaded image in the WMS reader:

Screen Shot 2023-10-19 at 2.36.44 PMIf you try the settings shown above, you will get an image with a reasonable pixel spacing:

Screen Shot 2023-10-19 at 2.38.12 PMScreen Shot 2023-10-19 at 2.39.11 PM

Hi @daveatsafe​ . Thanks for your response, that makes sense. I've added in the bounds based off what the metadata says. But how do I know what the map width and height is? Without that, I'm still not getting a spacing of 2m, as I would expect.

daveatsafe
Safer
Forum|alt.badge.img+19
  • daveatsafeSafer
  • Safer
  • October 20, 2023
hannahwh05 wrote:

Hi @daveatsafe​ . Thanks for your response, that makes sense. I've added in the bounds based off what the metadata says. But how do I know what the map width and height is? Without that, I'm still not getting a spacing of 2m, as I would expect.

Map width and height is the size of the resulting image in pixels. So if you want a 2m resolution, set the image width to (bounds maximum X - bounds minimum X)/2 and the image height to (bounds maximum Y - bounds minimum Y)/2.

hannahwh05
Contributor
Forum|alt.badge.img+5
  • hannahwh05Contributor
  • Author
  • Contributor
  • November 6, 2023
hannahwh05 wrote:

Hi @daveatsafe​ . Thanks for your response, that makes sense. I've added in the bounds based off what the metadata says. But how do I know what the map width and height is? Without that, I'm still not getting a spacing of 2m, as I would expect.

Thanks so much for this. Unfortunately, they updated the wms and I wasn't able to read it in again but will give this a try when I'm next able

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