Discussion: when you have no LIDAR

Trying to get some data to help me produce contours for Waller Park in Santa Maria / Orcutt, CA...

I can find 1/3 arc-second DEM on the USGS site, is that even useful? It gives me a 172 MB GeoTiff I'm not sure what I can do with.

Pretty flat? You're looking at maybe two contours, you could just trace them.
https://ngmdb.usgs.gov/topoview/viewer/#15/34.9031...

Sweet-looking venue, Backstreet Boy! From the Google Street View, it looks like there's a lot of small-scale bumpiness, so high-resolution elevation data would be useful. 1/3 arc-second is about 10m, so not super helpful for rendering the small shapes. But at least it would establish absolute heights across the area.

I think QGIS should be able to contour the DEM, but it has been a while since I've done this, so I've forgotten what I learned by bumbling through the process myself and wouldn't be able to help you with the details.

If you look at this link you should be able to download ("save and get") a georeferenced pdf map with 5 meter contours derived from the Copernicus satellite data. It isn't as good as LIDAR, but it works. Import the pdf into Inkscape and then save as a dxf file and you will be able to edit it in OCAD or OOmapper.

https://oomap.dna-software.co.uk/#/642dffddce09c/o...

If you export the same area from the standard version of Open Street Map as an .osm file you can import that directly into OOmapper to establish georeferencing and scale. If Open Street Map is missing some features then you can create an editing account and add them yourselves.

Here is how I do this in QGIS with the SRTM Downloader. I've gotten usable contours for a client in Germany this way where LiDAR wasn't available. Good enough for training! SRTM Downloader article

Thanks all!

First I ran the USGS data through QGIS and generated contours that unfortunately cross known hilltops.

Then I got the oomap with the 5m contours and converted it to GeoTiff and reprojected it in QGIS and it actually provided some usable contours to trace in OCAD. Need more, but it's a start.

I also did oomap with the SRTM and it didn't generate contours as good as SLO-30, so would I be able to do any better trying QGIS with the SRTM Downloader?

If you were able to get good say 1m contours on a flat area you may not be any the wiser. They can show shapes that are not visible to the orienteer. And the interesting little dimples that ARE noticeable could be randomly hit or missed. You may have to fieldwork them.

It's a flat park with prominent sand dune hills covered in forests. Need those hill shapes. Thinking I'll have to go walk the contours myself and get a GPS track

Check with the city (departmnt of public works or whatever). There's a possibility that they have an engineering map from when they did construction there that would be exactly what you need.

https://www.arcgis.com/home/webmap/viewer.html?web...

Didn't see contour data, but other useful layers and elevation might be hidden in one of the other data sets.

Thanks JJ and Clinton, yes I had checked the county's GIS site for anything and didn't find what I needed. The park is in the unincorporated town of Orcutt which has no such online presence.

I think it is very unlikely that an engineering map. like JJ refers to, would be noted on a GIS website.
True, it may not exist any more, but locating it would probably require person to person contacts.

I am currently working on an area which had a 10m DEM base. I describe the contour creation process as "hand-crafted". I use OOM on a gps enabled tablet and just try and walk what I perceive as the contours (in both directions) between what I believe are useful anchor points on the DEM contours. The gps trace acts as the basis of my final contour line.

If it’s mostly open, with just canopy from individual trees (rather than connected canopy), you can possibly get drone aerials and process them with Open Drone Map (ODM) to get an orthophoto and point cloud (a “dense point cloud”). For mostly open areas, you can get decent contours. Categorizing it (ground, buildings, vegetation, etc) can be a pain with lastools because of the very high number of points.

I have an area of overlapping commercial orthophotos from Pictometry (now EagleView). I’ll see if I can find an open area with adequate overlap and see if ODM will make the point cloud. I’m guessing this won’t work.

I’d think the county or city park office might have old construction maps.

It appears that area is having lidar flown this year. Zoom in and click here:

https://www.arcgis.com/apps/View/index.html?appid=...

I'm only semi-serious with this answer but...

if lidar doesn't exist... pick a different area to map. I basically won't work on areas without lidar data and the end product almost certainly won't be as high quality. One option is to get lidar flown but that can be quite expensive.

Of course, I recognize that some areas are unlucky and have very little if any lidar available in which case finding a different area with lidar might not be an option.

Yeah, normally I’d agree 100%. {edit: That is, don’t waste your time if there’s no lidar for woods maps.} But for a city park like this you could probably eyeball the contours. I could do the drone method I mentioned in a few hours (neglecting to mention this park is probably a drone no-fly-zone because of the airport. You’d need a Part 107 license to attempt it, I think).

Drone photos of a park worked a charm when I held an online mapping conference for a group of (former East Block) orienteers last year. The drone images were taken by the local mapper who asked me to hold the course. Yes, you get some white spots around/underneath big trees but absolutely no issues interpolating the contours across these voids.

California has a lidar status map. I think the area is planned and funded for 2023. Maybe just wait until that data is ready?

I don't know the typical timeline for acquisition, processing and then publishing. But for my local county and city, I got in touch with the GIS staff and asked them to let me know as soon as it was available. I was able to get the data a few months before it was published for online download.

@cedarcreek, good point! in complex urban sprint maps especially I get super creative with my contour drawing even if I do have good lidar. Drawing lidar accurate contours is not necessarily helpful to orienteers so I draw what I see with the lidar as a guide.