Latest Contributions by DavidMedeiros

‎04-25-2013

I'm a cartographer as well as a GIS professional and I think I have a decent handle on projections and how they effect the various attributes of map display. What I'm less clear on is the need to match a particular kind of projection with particular shape computations in the GIS. When a researcher or student here gets help with a project they will often be told to match their reference system to their computation, so equal area for a project looking at area calculations or equidistant for a project involving distance measurements or buffers etc. The implication is always that you will get incorrect results for area and distance if you used a mismatched projection (equal area for distances). I'm pretty sure this is not correct and that only the visual aspect of the map is at risk when mixing up the projection like this, but that calculations taken from two projections of the the same envelope but differing shape characteristics should be the same as long as the projection has real units like feet or meters. Can any one here verify this for me? Or correct me if I'm wrong? Thanks, David

‎04-18-2013

We have a mosaic data set of all ASTER 30m DEM tiles for the world that we frequently need to extract local areas from. My typical approach to extracting smaller sections from the mosaic file are to either 1) use the mosaic to determine the tile IDs for the study area and then copy just those tiles to a new raster file (mosaic to new raster); or 2) I use an existing polygon to Extract by Mask to get just the portion of the global mosaic that we need. Extract by Mask is more direct but I've found it's unreliable and only works some of the time for whatever reason. I've tried Clip but if I remember correctly it usually fails when clipping from a mosaic data set. Selecting the tiles always works but is tedious for larger areas and kinda defeats the purpose of having a mosaic. How can I use the mosaic data set to either automate selection of underlying tiles or to consistently get a good extraction of the mosaic data?

‎03-29-2013

Hi guys, The graphic is wrong and I've talked to the tool owner to have him update it. The tool, however, seems to be working as it should. See screenshot attached. I'm using 10.1 sp1 for this test. Best, Eric Just saw this after posting above, thank you for your reply.

‎03-29-2013

Did you try the "DATA" option? I thought I did but must have miss checked the box. It works as described, not as pictured, meaning the tool does in fact ignore individual cells of no data and not the entire stack of no data cells. ESRI should update the image to match.

‎03-27-2013

Did you try the "DATA" option? I just ran a test with the DATA option on a set of three dummy rasters: value1, value2, and valueNull. The result for mean should be 1.5 if the null values are being ignored, instead I got an output raster of Nulls. So that mean it ignore the entire cell stack, not just the individual null cells.

‎03-27-2013

I have a stack of rasters (daily UV values for a year). I need a yearly average raster but my input daily rasters contain null values through out each raster at various locations. If a cell stack has a null in it I still need the average of the remaining cells with real values, but not an average that counts the null cells for division. Will the Raster Calculator ignore the null value cells in the average or will it count that cell in the denominator value for the average function? I see that Cell Statistics has an option to ignore null value cells, which reads like it would be what I want but their graphic example seems to suggest that what it does is ignore the entire cell stack if one cell is null. http://resources.arcgis.com/en/help/main/10.1/index.html#/Cell_Statistics/009z0000007q000000/

‎03-22-2013

I'm still unclear exactly what step in the process makes the map visible to my Collector app but it works. It seems that adding an editable point service isn't enough, you have to go into the attribute schema and make changes there before it will show up.

‎03-22-2013

The biggest difference is that you need to have an editable point feature service (lines and polys are coming in a future release) in the map for it to be compatible with the Collector. If you want to share the map with me I can take a look. Ok, that's the critical piece of missing information. Thank you. I'll experiment with a point layer and see how that works.

‎03-22-2013

In the app itself from the sign in page there should be a link that says learn more you can tap that to get more information on how to author maps for data collection, that link will take you to http://resources.arcgis.com/en/collector/ where we have a few tutorials to help you get up and running. Once you've authored a map for collection, log in to the app with your organizational account and it should show up. I'll take a closer look at that. I followed what looked to me to be similar workflows for creating a map in ArcGIS online assuming anything I created there would be available as a map base in Collector. There must be a specific step in the map build process that makes it available to Collector?

‎03-21-2013

I just installed Collector for iOS and despite having a full ArcGIS online account I don't see any maps in the app once logged in. There are no maps visible under "All", My Maps", or my "Organization". I've logged in and out several times but nothing changes. What should I be seeing once logged in? It sounds like even a basic online account would show a series of maps available for viewing under "All".

‎03-18-2013

I have a researcher who is looking for the definition of the attribute field EDUCBASECY (2010 Pop 25+ Educ Attain Base) from the 2010 BA data. I don't see this listed in the variable list doc for my current BA dataset and can't find anything online other than the old 2010 variable list. I assume this is simply the total number of individuals per unit, that are 25+ and have attained some level of education (the base population). Any help is greatly appreciated. David

‎03-14-2013

Thanks for the reply Curtis. I'm the GIS research specialist helping Amy with her model and suggested she look to the forum for more help. Unfortunately the constraints of academic based GIS research are such that "learning python" isn't really an option for most researchers, especially those with no prior programming background. I've used iterators in model builder quite a bit but am not familiar with model variables (other than %name%). In your example ""TOMS_%year%m%month%*", where do the year and month model variables come from? Can we create a list for the years and add that as a variable to the model or do we need to run a search cursor to get all of the names first? I found this python tool for raster lists (http://resources.arcgis.com/en/help/main/10.1/index.html#/ListRasters/018v0000003w000000/). Is this what we need to nest, one list for yearly raster then another for each month in that year before running the CellStats tool? Appreciate the help, thanks. David

‎11-30-2012

David, I believe the limit should be around 3500 features unless this somehow changed. I will double check internally. Regards, Jason R. I just checked again, we are definitely running that add-in. The FAQ for the add-in says 100 records at a time. It says you can batch them 100 records at a time but selecting the next set of 100 records in our feature class doesn't seem to work so not sure how you add more records with out splitting your features up into separate 100 feature tables. I have groups of students who all found data they need from CA but for hundreds or thousands of records. Splitting their tables up is not really practical and the limit makes CA more or less useless to them. I was hoping to get a quick forum answer but this is looking like a larger problem for us, I'll probably move over to ESRI help next. Thanks.

‎11-29-2012

David, If you are using the Import File on the Select Location tab there will be a limit of 100 at a time. Based on what you are looking to do you might want to take a look at the Community Analyst Add-in for ArcGIS. It would allow one to not only run CA reports on a polygon feature but also an option to append that reports data back to the polygon layer. Also no limit of just 100 at a time. http://www.esri.com/software/arcgis/community-analyst/ca-addin Regards, Jason R. Thanks Jason, although that doesn't make any sense to me. As far as I know, I am already running the CA add-in to ArcGIS. It launches from inside ArcGIS and looks just like the screen shot in that link, but it still limits the number of features it will directly append to.

‎11-28-2012

I'm helping several groups of students use Community Analyst for their class projects. We've been extremely excited about how easily CA lets us explore census data. The problem is CA seems to be very limited in terms of actually letting you use that data directly in ArcGIS. It has a 100 record join limit and I haven't been able to figure out how to extend the first join into the next set of 100 records. Is there any way to join more than 100 features or records at a time? I can't see any way to download the raw tabular data instead of the aggregated report.

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My Ideas

Latest Contributions by DavidMedeiros

Projections effect on GIS computations? Area and distance measurements in the GIS.

Best methods for extracting or clipping from mosaic data set?

Re: will Raster Calculator ingnore null values?

Re: will Raster Calculator ingnore null values?

Re: will Raster Calculator ingnore null values?

will Raster Calculator ingnore null values?

Re: no maps visible once logged in

Re: no maps visible once logged in

Re: no maps visible once logged in

no maps visible once logged in

Definition for EDUCBASECY?

Re: How to aggregate rasters using raster file name?

Re: Community Analyst Record to Feature limit?

Re: Community Analyst Record to Feature limit?

Community Analyst Record to Feature limit?

Allow admins to reset orphaned offline use license...

Re: Rectified 16 bit tif appears black in PhotoSho...

Collect GPS locations by angle and distance offset...

Can you copy symbology from one Feature Layer to a...

Add an Extent parameter to Disperse Markers tool