Latest Contributions by MelitaKennedy

‎07-19-2016

Hi Pat, I have no official knowledge of those transformation parameters. They're not in the EPSG Geodetic Parameter Dataset, but they are similar to what's there (dx: -199.87, dy:74.79, dz:246.62). So, try this. In ArcMap, open data frame properties and select the Coordinate Systems tab. Click the Transformations button. The "Into:" box should say GGRS 1987. The "From" box should list both GGRS 1987 and WGS 1984. Select WGS 1984. Click the "Using:" pull-down and select GGRS_1987_To_WGS_1984. What we're seeing is if that gets rid of most of the offset. If it does, and you're happy with the results, you can stop. If you want to try the 7 parameter transformation that you received, open the Create Custom Geographic Transformation tool in ArcToolbox. 1. Give the new transformation a name like, GGRS 1987 to WGS84 7par 2. Set the source/input GCS to GGRS 1987. 3. Set the target/output GCS to WGS 1984. 4. Set the method to Position Vector (it could also be Coordinate Frame; try PV first as it's more common in Europe). 5. Fill in the parameter values. 6. Okay the dialog. A transformation-name.gtf file will be created and written to your data location. For example on Windows 7, mine is at C:\Users\<username>\AppData\Roaming\ESRI\Desktop10.4\ArcToolbox\CustomTransformations. You can copy that file between machines but it has to go into the same location (per user). Melita

‎07-18-2016

Introduction à l'installation et à la configuration d'ArcGIS for Desktop—Aide | ArcGIS for Desktop Je suis plein d'espoir que cela est utile pour vous (Google translation: I am hopeful that this is useful for you)

‎07-18-2016

Hello Patricia, Is the data using the GGRS87 Greek Grid or the older "Greek" datum/GeogCRS / Hatt projection? Are you setting any transformations? The most accurate transformations between the older Greek Grid (Hatt projection) and GGRS87 Greek Grid is a polynomial transformation that you would have to get from the government but Esri doesn't support polynomial transformations anyway. We have a Greek datum/GeogCRS to GGRS87 transformation in version 10.0. There's also a GGRS87 to WGS84 transformation. If you haven't been, trying setting the corresponding transformation in ArcMap (data frame properties, Coordinate Systems tab, Transformations button). Melita

‎07-12-2016

I wish I'd seen this earlier. Numbers are stored in the units of the coordinate system, so yes, they can be in English units, smoots, yards (several varieties), and a bunch of others.

‎07-11-2016

If the table lists easting/northing values, that should be fine unless they're ground coordinates rather than grid (projected) coordinates. I have a feeling that the plat has more information like the direction of the lines that these station coordinates plus offsets refer to. Melita

‎07-08-2016

Carina, What version of ArcGIS are you using? Based on your comment about the Define Projection tool, I am wondering whether some data layers now have incorrect coordinate systems (projections). For instance, for the rasters that have cell sizes in degrees, what coordinate system do they have? They should have a geographic one like WGS84. Even if the layers are all using a geographic coordinate system, and the data frame is too, the measure tool should default to measuring geodesic distances and some linear unit. Because of that, I am wondering whether data frame/layers have projected coordinate systems, but the data (coordinates) themselves are still in degrees. Melita

‎07-01-2016

If your data's RTK then it's not on NAD 1983. You'll get access to other transformations if you use a later realization like NAD 1983 (2011) or NSRS2007. I would recommend using WGS_1984_(ITRF08)_To_NAD_1983_2011 instead, for instance. Equation-based transformations (coordinate frame, position vector, Molodensky-Badekas, geocentric translations) will also give (slightly) different results if you run them with or without ellipsoidal heights.

‎07-01-2016

Wow, that brings back memories. Jim Mossman of Data Deja View created a bunch of symbol and font files for ArcView GIS and ArcGIS. I do not know if they will work with current versions of ArcGIS, but you can download the California files here. Melita

‎07-01-2016

Yes, that's correct.

‎06-27-2016

An equidistant conic projection maintains distances along the standard parallels, and along longitude lines (those aren't north-south except the central meridian when projected). Calculating the geodetic distance is on the ellipsoidal/spheroidal surface so it doesn't take elevations into account. So, in general, I would expect your time-based-on-distance routes to be too short.

‎06-23-2016

While fine-tuning a technical workshop for next week, my co-presenter and I realized that our comment of "don't forget these knowledge base articles!" (see terminology note below) wasn't very helpful. You used to be able to go to http://support.esri.com and type in a knowledge base/technical article number like 23025. That would bring up "FAQ: Projection Basics: What the GIS Professional needs to know." The Support website has been redesigned and that trick no longer works. Below I've included the new links to some of the useful coordinate systems, map projections, and geographic (datum) transformations technical articles. 23025: http://support.esri.com/technical-article/000005562, FAQ: Projection Basics: What the GIS professional needs to know 17420: http://support.esri.com/technical-article/000002813, FAQ: Where can more information be found about coordinate systems, map projections, and datums? 29129: http://support.esri.com/technical-article/000007880, How To: Identify the spatial reference, projection, or coordinate system of data 21327: http://support.esri.com/technical-article/000004829, How To: Select the correct geographic (datum) transformation when projecting between datums 24893: http://support.esri.com/technical-article/000006217, How To: Identify an unknown projected coordinate system using ArcMap 29035: http://support.esri.com/technical-article/000007831, How To: Define the projection for CAD data for use in ArcMap If you have a favorite KB/technical article number, you can also append the number to this partial link: http://support.esri.com/en/knowledgebase/techarticles/detail/ which will automatically redirect to the new URL. Terminology note: Originally, they were called knowledge base articles and sometimes referred to as KB articles. A few years ago, the name was changed to technical articles.

‎06-23-2016

Yes, because a PCS extent may be tipped relative to the "graticule" in lat-lon space. We treat the graticule (system of latitude-longitude lines) as if it's a flat, 2D grid, so the extent of a PCS may end up at an angle, a trapezoid, etc. after it's unprojected. Melita

‎06-17-2016

Marina, no projection parameters?

‎06-17-2016

The EPSG online registry website allow you to enter an extent and will then return any coordinate systems that match. But you then have to still check the parameters (mainly the false easting/northing ones) to see if the coordinates would match up.

‎06-16-2016

Marina, Those values don't look like UTM. If the data's in the US, they could be State Plane instead. If the data's scattered across, even a state (let alone multiple states), you may have to figure out which zone each one is in first. Ouch. UTM X coordinates should be between 200000 and 800000 meters, while in the contiguous US, Y values are between 2.5 million and 5.5 million meters. I didn't spot an obvious state plane zone that matched 2million,2million either. If you can post approximately where the data is located, I can see if I can find a matching coordinate system. You can do this yourself by adding a base map/other data to ArcMap and setting the data frame's coordinate system to the one you want to check. Make sure the display units match the coordinate system and just read off the coordinates from the status bar (at bottom right of map). EDIT: You said that the data's in Canada, above Idaho. Is it in BC or Alberta? We have a few provincial coordinate systems, but they're generally putting the data pretty far North. Nearest major feature? Thanks! Melita

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