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#16
Martin Gamache

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I tried to thin out the graticule cells by deleting the non land (non intersecting) cells and it could select them find but crashes when trying to delete them.


To weed out the cells you don't need in ArcGIS Desktop how about selecting the ones you want to keep and exporting just the selected features as new data?



Def. worth trying.

Thanks

#17
Martin Gamache

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I tried to thin out the graticule cells by deleting the non land (non intersecting) cells and it could select them find but crashes when trying to delete them.


To weed out the cells you don't need in ArcGIS Desktop how about selecting the ones you want to keep and exporting just the selected features as new data?



Def. worth trying.

Thanks



Export Failed !!!

#18
mdsumner

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Here is what I'm trying to do. I have the WWF ecoregions dataset ( about 14,000 polygons) I am trying to calculate some statistics about how many of these 5' cells would fall within each polygon and how many would be split by polygon boundaries. Too me it seemed like a fairly simple vector problem, but it turns out to be a very huge dataset. I'm doing it with a raster grid now, but I'm not sure if I'll be able to answer the second question easily.

mg


Why do you want to do that? Surely the actual answer as you've described is not what you are finally after?
What is the result you want after you've obtained those summaries of your 5' cells? Perhaps there's another way to think about it? Mathematically there's really no need to generate the vector grid at all, but how to interrogate the WWF dataset with the implicit grid sequencing depends on what you're trying to achieve. As someone noted, it's really the display of the vertices that will choke some GUIs, I'd be keen to try this problem in R or the like.

Also, what about tiling the the thing into 4 (or more) parts and then doing the clip/overlays in stages? Manifold (on your 3Gb ram machine) would certainly handle that.

(Naively it sounds like the old school projects to approximate area calculations, but I'm sure there's more to it than that ;) )

#19
Martin Gamache

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We are planning a modelling exercise to look at factors influencing global biodiversity ( at the taxa level) in the world's ecoregions. Alot of our predictor datasets are available a 5 arc minute resolution and we wanted to see what kind of overlap we have at the ecoregion boundaries to determine if that resolution would be adequate. So it does necessitate making estimates of the proportions of cells that are entirely within the polygons vs those that overlap the boundaries and providing counts and area estimates for each ecoregion.

So it is a spatial problem.


Dividing the dataset up is my next step if I still have problems now that I've removed the non terrestrial grid cells. I was hoping to avoid that but....


I was finally able to get Arc to export the selected ocean cells today when I had it write the export file to a different drive than the one where the source file resided. Seemed to increase the speed of the whole process as well.

mg

#20
mdsumner

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What about Orthogonalizing the regions dataset to 5' then doing an overlay/ clip with the original to see what proportions of the two overlap?

I'm thinking out aloud here, but it might be an avenue to explore.

#21
MapMedia

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Have you tried doing it in raster? Convert WWF into grid then do a zonal summary into 5" polygons or something.

#22
DaveB

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I was finally able to get Arc to export the selected ocean cells today when I had it write the export file to a different drive than the one where the source file resided. Seemed to increase the speed of the whole process as well.
mg


That's good. :)

If you can/want to share the data I could try to see if there is an issue we need to look into at ESRI, and/or give it a try in 9.2 since we have done a lot to improve performance for the upcoming release.

Let me know and I will e-mail you with particulars about uploading to our ftp site.
Dave Barnes
Esri
Product Engineer
Map Geek




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