Archive for the 'GIS' Category

ESRI ArcMap and commas

Published by
Nif
at November 29, 2007 in GIS. 0 Comments

Quick post here.

I just wasted about and hour or two because of commas in the row names in a dbf imported into ESRI.

I got “unknown errors” and lots and lots of crashes. But the funny thing was I could display and manipulate the data to my hearts content as long as it was an “Event”.

As soon as I wanted to make my XY events more permanent - BOOM - and a lot of keyboard slamming ensued.

So my question to ESRI is 1) Why let it work at all with invalid characters in the Row names and 2) How about giving me a clue on the error - unknown error is a cop out.

Thats’ all - gotta go fix my personal life now.

Coordinate Conversion - again

Published by
Nif
at October 23, 2007 in GIS, GPS, Geospatial, Mapping and Photo Sharing. 0 Comments

So it seems that most of the hits on my site are from people looking for coordinate conversion info.

Besides the links for online conversion that I listed a few posts ago… there is a great desktop program for coordinate conversion. It is called Corpscon.

The link is here: http://crunch.tec.army.mil/software/corpscon/corpscon.html

This is by far the most accessible and easiest to use coordinate conversion program and I used it all though my Geodesy/GIS/Remote Sensing/Photogrammetry studies way back when. This program

“…allows the user to convert coordinates between Geographic, State Plane, Universal Transverse Mercator (UTM) and US National Grid systems on the North American Datum of 1927 (NAD 27), the North American Datum of 1983 (NAD 83) and High Accuracy Reference Networks (HARNs). Corpscon uses the National Geodetic Survey (NGS) program Nadcon to convert between NAD 27, NAD 83 and HARNs.”

It totally kicks ass and I have used it many a time to check where coordinates should be in a particular coordinate system.

dms to dd and reverse

Published by
Nif
at October 11, 2007 in GIS, GPS, Geospatial, Location and Photo Sharing. 2 Comments

Coordinate conversion - who thinks about this?   Don’t know, but  it’s kinda important.

There are sites out there that allow you to look up the coordinates for millions and zillions on places on earth such as, GeoNames.org or you can open up GoogleMaps or Google Earth and zoom into your desired spot and write down the coordinates.

But - there they are in the standard Degrees, Minute, Second format (DMS) not Decimal Degrees (DD) which are so much easier to work with in GIS programs.

Now I realized that yes, you can change this feature in the Google Earth options and that the coordinates are embedded, in DD format, in the “Paste This” code in Google Maps, but both of these options require me to, well, think too much about where exactly in Winnipeg, Canada I want my dot to fall. Is it a centroid? Is it somewhere in a polygon? Nooooo - I don’t want to think - I just want a point.

GeoNames is a great alternative and I believe is based off of point representation of places.  I just type in Winnipeg (misspelled even!), it corrects me and gives me my selection of Winnipegs with the most probable at the top.  BUT the values are in DMS.

So then I go out on the web to find a DMS to DD converter.

The coolest converter I found out there will allow you to convert not only from DMS to DD and reverse, but has some functionality for UTM to DD/DMS with datum selections!

http://www.oasisphoto.com/navigation/convert_form.php

Another good one from the North Carolina Dept of Engr and Natl Resources allows you to convert between a few coordinate systems, datums, and just plain DMS to DD.  It’s a little clunky on the interface though, requiring you to type “deg” after your degree value.

http://gis.enr.state.nc.us/GISInterface/convert/default.htm

But for the simple job of just converting from DMS to DD or vice versa this one from the FCC of all places does the trick with one more decimal place then OasisPhotos site. And Xavier Jubier’s converter gives you even one more decimal place!

http://www.fcc.gov/mb/audio/bickel/DDDMMSS-decimal.html 

or

http://xjubier.free.fr/en/site_pages/DMS2DD_Converter.html 

It doesn’t matter what datum your datum is in if you are just using these programs just to convert from DMS to DD - it’s just basic math equation.  But it is important to assign a datum (even to lat/long) values when you plot the results.

The precision of your original data determines how many decimal places you should be concerned with.

For example, if you only have something like 49º53′ (and don’t even have a seconds value) then you really only need something like 2 or 3 decimal places to represent the minutes value. So your working result would be 49.883.

I have to go back to work now.