Field Checking ready to begin

The time has finally arrived. I have a good basemap consisting of LIDAR contours and aerial photos, and I have permission to make the map. Now all that is required is that I spend the time on the ground. This will take at least a year, maybe longer, depending on the level of detail that I encounter.

It's exciting to start a new map, but it's also a little sad. All the secrets of the park will be revealed. Every boulder, every fallen tree, every ditch and gully will be pinpointed (I hope) and drafted on the map. Making an orienteering map is a little like submitting to a full-body search - with photos. There will be no spot left unexamined by the time I am through.

And sometime in the not too distant future, several hundred orienteers will be handed the new map and sent out to see and find for themselves the hidden treasures of the park.

I have also added new photos to the Picasa web album I am keeping. I was out there (in the rain) last Saturday doing an "inventory" of boulder sizes. This is not mapping, but a walkthrough to set some standards. What will be the smallest boulder that I will map? Probably waist-high, unless it is a solitary boulder separated from its cousins. I also found very few rootstocks (fallen trees) and minimal ditches and gullies, but I restricted this inventory to just the area east of the bare rock.

LIDAR contours

The map took a major step forward this week with the acquisition of LIDAR contour data from the Coweta County GIS department. LIDAR is the latest and greatest method of generating contours (and other data) using airborne radar and digital signal processing. This is great news, and should make the finished product much better.

Getting it into a usable form took most of a day. The county supplied two foot contours in a shape file. I had to use qgis, wich is an open source GIS program (free) to translate it from lat/long coordinates to UTM WGS84 in zone 16N. Then I used a demo program to convert from shape to dxf. The dxf file still needed some massaging, which I did with sed in OS X. After all that I was able to import the dxf and have it magicall line up with the geo-referenced aerial photos.

Here's an example.The purple lines are the lidar data. The green lines are the USGS contours from the DRG. The blue lines are contours generated from the USGS DEM. There's a lot of difference.

[caption id="attachment_64" align="alignright" width="425" caption="LIDAR Contour Example"][/caption]

GAOC board approves mapping project

I submitted a proposal to GAOC and they approved it. So now I have permission from the DNR and the blessing of the orienteering club so I am good to go. Can't go out to the park again until after turkey season is over, and by then the leaves will be out. Should be able to work on the open fields and pine plantations in the horseshoe bend this summer, and then move into the woods after the leaves drop in the fall.

Progress Map and Project Time pages

I added two more pages, links are over on the left. A spreadsheet of the time I'm spending on the project, and a map of my field checking progress.

GPS -> DXF -> OCAD

The next piece of the puzzle that I needed to solve was how to et the GPS waypoints into OCAD easily. The scenario is that I mark a waypoint of a boundary marker or a boulder or that old abandoned corn combine while I am out field checking. Then, when I get back in front of the computer I magically transfer that point into OCAD.

OCAD is not a full featured GIS application, at least not version 8. It only acepts DXF files, which are an ancient output format of autocad. Wikipedia has a nice page explaining the format and a link to the official definition. OCAD doesn't need a full fledged file, ust the points section. Here's an example with just two points:

0
SECTION
2
ENTITIES
0
POINT
8
cbwaypoints
10
688166
20
3701504
30
0
0
POINT
8
cbwaypoints
10
688222
20
3701658
30
0
0
ENDSEC
0
EOF

I was able to take the gpsx file from the GPS, and using GPSBabel and a perl program I wrote for my Mac, massage it into the correct format. As long as I name the waypoints in a certain format, I can grep them and convert to a dxf fle.

OCAD imports these in a gray color, marked with a plus sign, with no symbol defined. It's necessary to select them and convert them to the appropriate symbol.

Now it remains to be seen how accurate they are. This is the first time I have attempted to use GPS for making an orienteering map. I guess I will report back in May on the success or failure of this experiment.

DEM -> contours -> OCAD revisited

I have begun construction of the basemap in earnest. All my datasets had to be converted to WGS84, since it turns out that my consumer grade GPS only outputs waypoints in that coordinate system. I will display in other coordinate systems, but not output them.

The gdal utilities to the rescue. gdalwarp will convert any raster dataset to a different coordinate system, so I was able to get all my datasets and aerial photos into WGS84 with no problem.

I them used gdal again to generate three meter contours from the dems. Exporting to dxf presented a problem again, since my free trial period for arcv2cad had expired. Fortunately I found a free utility that would convert from shape files to dxf. DXF Author from Massachusetts GIS, does the job well and is free.

Cleanup with Friends of Chattahoochee Bend

The Friends of Chattahoochee Bend State Park had a cleanup event last Saturday and I showed up to help. There were a couple of dozen people, and we got an update on the park status, then headed out to the park to pick up trash.

Like most rural areas, there has been plenty of illegal dumping going on over the years. We spent a few hours cleaning up several of these dumping sites along the county road that runs through the park and the power line that crosses it.

It was a good start - more work is needed, of course. The bare rock areas are rimmed with trash too.

After the trash pickup I wandered around in the bare rock areas for a couple of hours checking things out. Looks like there will be plenty of detail in some areas and almost no detail in other areas.

We got some good news about the hunting. Looks like they will change to a quota hunt or only a few days. This is how hunting is handled at FDR, Red Top, Lake Russell, Joe Kurz, and Dukes Creek. This means I can map in the winter, which is a much better time because of the increased visibility.