Hi Anthony,
It can be tricky getting these simulations set up. Often, the resolution and spatial coverage of the habitat data do not match up very well with the currents
data; e.g. often the habitat data are available at relatively fine scale and extend right up to shore, while the ocean currents data come from coarse-scale models optimized for pelagic areas and that do not extend right up to shore. Or the currents models
do not incorporate critical processes that strongly affect near-shore transport, such as tides.
If you are working in a coastal environment it can be a challenge getting a simulation working. If this involves extrapolating the ocean currents toward shore,
there is not only the logistical difficulty of getting the layers set up with data in all the cells that need it, but also the more scientific question of whether those extrapolated currents values are realistic. I will set aside this latter question but I
do urge you to consider it carefully. For now, I’ll try to help you get it running so you can see some results.
The -128 is suspicious. My guess is that you have valid patches with IDs ranging from 1 to 127. In that case, ArcGIS may sometimes store them in a raster with
a pixel data type of 8-bit signed integer, with -128 as the “no data” value. MGET should recognize the no data value, if it has been designated within the raster. It sounds like that is not happening. In that case, MGET would believe that all of your land
pixels would be one giant habitat patch with value -128, which obviously you don’t want! You should check in ArcMap that when you display the patch ID raster that it shows no data for land, rather than -128.
If that’s happening, there might be a bug in MGET, or this might be related a known problem in ArcGIS’s with 8-bit integer rasters. If the patch ID raster looks
ok in ArcMap, you are welcome to send me a zip file of your simulation directory and I’ll take a look to see what is happening. If the zip is more than 15 MB, please don’t email it, but use a file sharing service (e.g. Dropbox or Firefox Send). Also please
tell me your ArcGIS version, and send me a full transcript of what happens when you run the Load Currents tool (you can copy/paste the text from the geoprocessing window into email).
Best,
Jason
From: <>
On Behalf Of Anthony Snead
Sent: Saturday, November 2, 2019 7:58 PM
To:
Subject: [mget-help] Missing ocean current data
Good evening,
Sorry for bothering you all again, but I have a slight issue. I have received the following error after I have attempted to fix it multiple times.
“
Warning: The ocean currents images are missing data for some cells flagged as
habitat patches. This will affect the accuracy of the simulation. The simulator
will assume the ocean currents have a velocity of zero in these cells. Larvae
can only exit these cells via diffusion. These cells may retain larvae in a
manner that is not realistic. The IDs of the affected patches are: -128, 1, 2”
I have tried to load the ocean current data multiple times using different methods for estimating missing current parameters and the error persists. Do you have any way of remedying this. Additionally are the IDs are patch IDs or are they
something else because I have no patches in my data set with a -128 ID. It may be that my populations are really close to shore and the resolution has led to all of my layers extending slightly over land (even my water mask). Thanks for your expertise. I appreciate
it.
Respectfully,
Anthony A. Snead
PhD Student
Earley Lab
The University of Alabama
Department of Biological Sciences