Terrain data for showing AGL

[error414]

Hi,

I play with rangefinders, but rangefinders are expensive, inaccurately, or both.

Solution could be implement into inav terrain data saved on SD card similar to ardupilot. https://terrain.ardupilot.org . Precise for ardupilot is 30 or 10m, it's not enought for mountains, so would be nice to implement 1m precission from GeoTiff as well, lot of countries provide data for free.

At start AGL can be showed only in OSD, no any automations.

https://discuss.ardupilot.org/uploads/default/original/3X/5/e/5e1711b608419ec2c58a96824a0c281168ebe38d.png

[b14ckyy]

Some day in the future, when we have a SD card driver that is capable of reading and writing blackbox, maybe. And yes I am all down for that :)
Especially as it would come in handy for a 8.0 feature thats in the works.

[error414]

Some day in the future, when we have a SD card driver that is capable of reading and writing blackbox, maybe. And yes I am all down for that :) Especially as it would come in handy for a 8.0 feature thats in the works.

I'm not sure what do you mean about SD card driver.

Maybe it's naive idea but current SD driver (AsyncFatFS + sdcard_spi) supports.

afatfs_fopen afatfs_fseek afatfs_fread

file is represented by afatfsFilePtr_t so I would say it's possible to open multiple files. We don't need possibility to write file over mass storage to SD card. You can take SD card, put it to PC, copy "NXXeXXX.dat" file to root of SD card.

Then load "mavlink grid" could be easy (2048 bytes).

[b14ckyy]

@error414 I don't know the technical details but the current way INAV access the SD card has a lot of issues.
We can't even write blackbox at 1000Hz or more reliably on most MCUs without getting data errors. Taking cycle times to read data while blackbox is writing, does not seem to work reliably at all. That's what a few devs have told me.

[sensei-hacker]

Maybe it's naive idea but current SD driver (AsyncFatFS + sdcard_spi) supports.

afatfs_fopen afatfs_fseek afatfs_fread

a file is represented by afatfsFilePtr_t so I would say it's possible to open multiple files.

It's possible. Note that the SPI interface is much slower than the SD interface, which requires dedicated SD hardware. That may or may not be an issue. The SPI interface uses the same wire for commands as it does for data, so switching over to read, then reading data, switching back to write and writing some blackbox data will take time.

Keep in mind also F722 MCUs have a total of 512K flash and we've already had to remove features from the F722 builds in order to fit INAV in 512K. So a few more bytes matters - if the additional functions are another kilobyte that's an issue.

You are more than welcome to play with this and do a POC.

[error414]

The idea is still in my mind :). I did some research and I was able to create proof of concept of calculating position of tile (32*28 points).

Performance:

1. calculating position of tile uses mainly float, so it need fast FPU.
2. one tile has 2048bytes, tile cache I set currently to 5, it means 10kB in RAM. fuuu
3. reading one tile from SD card via SDIO could take around 1ms.
4. if we don't use cache, then new tile is needed approx each 11s. One tile is arounf 1km^2 (30m spacing), tiles overlap neighbor tiles, so no rapid reading from SD card.

Problems:
reading from SD card is main issue of this project, INAV uses pseudo async writing to SD card. I don't think we will find better solution for FW which does not use RTOS. For cooperation with blackbox there would be necessary create some mutex, or if user would like to use terrain altitude, then disable blackbox writing.

Personally I would allow this functionality only for H7 boards with SDcard slots which use SDIO. I would not allow it for SPI interface.

Any idea how to do that correctly, in personal project I use only chibios, and have not idea how to that in right way. I'm a litle bit scared of not possibility to interupt reading/writing if takes it too long.

[b14ckyy]

Sounds really cool. Personally I am fine with features exclusive for H7 boards. Maybe also include F765 as well. There is just a handful of boards and the chip is not used on new FCs anymore but still has 512k ram that is barely half used and SDIO.

Is the loading from SD done independently from the loop time? if it takes 1ms and halts any other process in the time, it would not work with dshot I assume.

[error414]

1ms is total time to reading 2kB. Inav uses library https://github.com/thenickdude/asyncfatfs . Not sure how it exactly works, but would say that it writes/reads in chunks each time you call sdcard_poll function. It's the probably best solution we can reach in INAV.

So far it's only theory, I don't have device with sdcard slot for testing. I orderd matek H743 wing V3.